[RFC PATCH for 5.2 00/10] Restartable Sequences selftests updates

[RFC PATCH for 5.2 00/10] Restartable Sequences selftests updates

[Mathieu Desnoyers]

Those rseq selftests updates are hereby submitted for feedback.

They change the per-architecture pre-abort signatures to ensure those
are valid trap instructions.

The way exit points are presented to debuggers is enhanced, ensuring
all exit points are present, so debuggers don't have to disassemble
rseq critical section to properly skip over them.

Also, discussions with the glibc community is reaching a concensus
of exposing a __rseq_handled symbol from glibc to coexist with
rseq early adopters. Update the rseq selftest code to use this
symbol.

Feedback is welcome.

Thanks,

Mathieu

Martin Schwidefsky (1):
  rseq/selftests: s390: use trap4 for RSEQ_SIG

Mathieu Desnoyers (9):
  rseq/selftests: Add __rseq_exit_point_array section for debuggers
  rseq/selftests: Introduce __rseq_cs_ptr_array, rename __rseq_table to
    __rseq_cs
  rseq/selftests: Use __rseq_handled symbol to coexist with glibc
  rseq/selftests: s390: use jg instruction for jumps outside of the asm
  rseq/selftests: x86: use ud1 instruction as RSEQ_SIG opcode
  rseq/selftests: arm: use udf instruction for RSEQ_SIG
  rseq/selftests: aarch64 code signature: handle big-endian environment
  rseq/selftests: powerpc code signature: generate valid instructions
  rseq/selftests: mips: use break instruction for RSEQ_SIG

 tools/testing/selftests/rseq/rseq-arm.h   | 132 ++++++++++++++++++++++++++----
 tools/testing/selftests/rseq/rseq-arm64.h |  74 ++++++++++++++++-
 tools/testing/selftests/rseq/rseq-mips.h  |  87 +++++++++++++++++---
 tools/testing/selftests/rseq/rseq-ppc.h   |  90 ++++++++++++++++++--
 tools/testing/selftests/rseq/rseq-s390.h  |  78 ++++++++++++++++--
 tools/testing/selftests/rseq/rseq-x86.h   | 120 +++++++++++++++++++++++++--
 tools/testing/selftests/rseq/rseq.c       |  55 +++++++++++--
 tools/testing/selftests/rseq/rseq.h       |   1 +
 8 files changed, 583 insertions(+), 54 deletions(-)

-- 
2.11.0

[RFC PATCH for 5.2 01/10] rseq/selftests: Add __rseq_exit_point_array section for debuggers

[Mathieu Desnoyers]

Knowing all exit points is useful to assist debuggers stepping over the
rseq critical sections without requiring them to disassemble the content
of the critical section to figure out the exit points.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-arm.h   | 52 +++++++++++++++++
 tools/testing/selftests/rseq/rseq-arm64.h | 52 +++++++++++++++++
 tools/testing/selftests/rseq/rseq-mips.h  | 53 +++++++++++++++++
 tools/testing/selftests/rseq/rseq-ppc.h   | 66 ++++++++++++++++++++++
 tools/testing/selftests/rseq/rseq-s390.h  | 55 ++++++++++++++++++
 tools/testing/selftests/rseq/rseq-x86.h   | 94 +++++++++++++++++++++++++++++++
 6 files changed, 372 insertions(+)

diff --git a/tools/testing/selftests/rseq/rseq-arm.h b/tools/testing/selftests/rseq/rseq-arm.h
index 3cea19877227..17e8d231943a 100644
--- a/tools/testing/selftests/rseq/rseq-arm.h
+++ b/tools/testing/selftests/rseq/rseq-arm.h
@@ -42,6 +42,19 @@ do {									\
 	__RSEQ_ASM_DEFINE_TABLE(0x0, 0x0, start_ip,			\
 				(post_commit_ip - start_ip), abort_ip)
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(exit_ip) ", 0x0\n\t" \
+		".popsection\n\t"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)		\
 		RSEQ_INJECT_ASM(1)					\
 		"adr r0, " __rseq_str(cs_label) "\n\t"			\
@@ -87,6 +100,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -149,6 +167,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -215,6 +238,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -267,6 +293,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -337,6 +368,11 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -408,6 +444,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -486,6 +528,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		"str %[src], %[rseq_scratch0]\n\t"
 		"str %[dst], %[rseq_scratch1]\n\t"
 		"str %[len], %[rseq_scratch2]\n\t"
@@ -605,6 +652,11 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		"str %[src], %[rseq_scratch0]\n\t"
 		"str %[dst], %[rseq_scratch1]\n\t"
 		"str %[len], %[rseq_scratch2]\n\t"
diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
index 954f34671ca6..2079f71e0ca2 100644
--- a/tools/testing/selftests/rseq/rseq-arm64.h
+++ b/tools/testing/selftests/rseq/rseq-arm64.h
@@ -95,6 +95,19 @@ do {										\
 	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,			\
 				(post_commit_ip - start_ip), abort_ip)
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)				\
+	"	.pushsection __rseq_exit_point_array, \"aw\"\n"			\
+	"	.quad " __rseq_str(start_ip) ", " __rseq_str(exit_ip) "\n"	\
+	"	.popsection\n"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)			\
 	RSEQ_INJECT_ASM(1)							\
 	"	adrp	" RSEQ_ASM_TMP_REG ", " __rseq_str(cs_label) "\n"	\
@@ -182,6 +195,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -231,6 +249,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -282,6 +305,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -325,6 +351,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -379,6 +410,11 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -433,6 +469,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error3])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -490,6 +532,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
@@ -545,6 +592,11 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1, 2f, 3f, 4f)
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(2f, %l[error2])
+#endif
 		RSEQ_ASM_STORE_RSEQ_CS(2, 1b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
 		RSEQ_INJECT_ASM(3)
diff --git a/tools/testing/selftests/rseq/rseq-mips.h b/tools/testing/selftests/rseq/rseq-mips.h
index 7f48ecf46994..25d10ff54769 100644
--- a/tools/testing/selftests/rseq/rseq-mips.h
+++ b/tools/testing/selftests/rseq/rseq-mips.h
@@ -68,6 +68,20 @@ do {									\
 	__RSEQ_ASM_DEFINE_TABLE(0x0, 0x0, start_ip, \
 				(post_commit_ip - start_ip), abort_ip)
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip) \
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t" \
+		LONG " " U32_U64_PAD(__rseq_str(start_ip)) "\n\t" \
+		LONG " " U32_U64_PAD(__rseq_str(exit_ip)) "\n\t" \
+		".popsection\n\t"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs) \
 		RSEQ_INJECT_ASM(1) \
 		LONG_LA " $4, " __rseq_str(cs_label) "\n\t" \
@@ -114,6 +128,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -174,6 +193,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -238,6 +262,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -290,6 +317,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -358,6 +390,11 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -427,6 +464,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3f, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -501,6 +544,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		LONG_S " %[src], %[rseq_scratch0]\n\t"
 		LONG_S "  %[dst], %[rseq_scratch1]\n\t"
 		LONG_S " %[len], %[rseq_scratch2]\n\t"
@@ -617,6 +665,11 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		LONG_S " %[src], %[rseq_scratch0]\n\t"
 		LONG_S " %[dst], %[rseq_scratch1]\n\t"
 		LONG_S " %[len], %[rseq_scratch2]\n\t"
diff --git a/tools/testing/selftests/rseq/rseq-ppc.h b/tools/testing/selftests/rseq/rseq-ppc.h
index 52630c9f42be..24f95649d71e 100644
--- a/tools/testing/selftests/rseq/rseq-ppc.h
+++ b/tools/testing/selftests/rseq/rseq-ppc.h
@@ -63,6 +63,19 @@ do {									\
 		"std %%r17, %[" __rseq_str(rseq_cs) "]\n\t"			\
 		__rseq_str(label) ":\n\t"
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".quad " __rseq_str(start_ip) ", " __rseq_str(exit_ip) "\n\t" \
+		".popsection\n\t"
+
 #else /* #ifdef __PPC64__ */
 
 #define STORE_WORD	"stw "
@@ -80,6 +93,20 @@ do {									\
 		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) "\n\t" \
 		".popsection\n\t"
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)				\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"		\
+		/* 32-bit only supported on BE */				\
+		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(exit_ip) "\n\t"	\
+		".popsection\n\t"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)			\
 		RSEQ_INJECT_ASM(1)						\
 		"lis %%r17, (" __rseq_str(cs_label) ")@ha\n\t"			\
@@ -169,6 +196,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -224,6 +256,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -286,6 +323,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -337,6 +377,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -400,6 +445,11 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -465,6 +515,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		/* cmp cpuid */
@@ -532,6 +588,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* setup for mempcy */
 		"mr %%r19, %[len]\n\t"
 		"mr %%r20, %[src]\n\t"
@@ -601,6 +662,11 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* setup for mempcy */
 		"mr %%r19, %[len]\n\t"
 		"mr %%r20, %[src]\n\t"
diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index 1069e85258ce..b8b5b6f900af 100644
--- a/tools/testing/selftests/rseq/rseq-s390.h
+++ b/tools/testing/selftests/rseq/rseq-s390.h
@@ -44,6 +44,19 @@ do {									\
 		".quad " __rseq_str(start_ip) ", " __rseq_str(post_commit_offset) ", " __rseq_str(abort_ip) "\n\t" \
 		".popsection\n\t"
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".quad " __rseq_str(start_ip) ", " __rseq_str(exit_ip) "\n\t" \
+		".popsection\n\t"
+
 #elif __s390__
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
@@ -55,6 +68,19 @@ do {									\
 		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) "\n\t" \
 		".popsection\n\t"
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(exit_ip) "\n\t" \
+		".popsection\n\t"
+
 #define LONG_L			"l"
 #define LONG_S			"st"
 #define LONG_LT_R		"ltr"
@@ -102,6 +128,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -160,6 +191,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -220,6 +256,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -268,6 +307,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -339,6 +383,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, rseq_cs)
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, 4f)
@@ -407,6 +457,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		LONG_S " %[src], %[rseq_scratch0]\n\t"
 		LONG_S " %[dst], %[rseq_scratch1]\n\t"
 		LONG_S " %[len], %[rseq_scratch2]\n\t"
diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h
index a5341044a2f5..0668608d3674 100644
--- a/tools/testing/selftests/rseq/rseq-x86.h
+++ b/tools/testing/selftests/rseq/rseq-x86.h
@@ -58,6 +58,19 @@ do {									\
 	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,		\
 				(post_commit_ip - start_ip), abort_ip)
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".quad " __rseq_str(start_ip) ", " __rseq_str(exit_ip) "\n\t" \
+		".popsection\n\t"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)		\
 		RSEQ_INJECT_ASM(1)					\
 		"leaq " __rseq_str(cs_label) "(%%rip), %%rax\n\t"	\
@@ -93,6 +106,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -149,6 +167,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -207,6 +230,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -251,6 +277,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -320,6 +351,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -386,6 +423,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		"movq %[src], %[rseq_scratch0]\n\t"
 		"movq %[dst], %[rseq_scratch1]\n\t"
 		"movq %[len], %[rseq_scratch2]\n\t"
@@ -535,6 +577,19 @@ do {									\
 	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,		\
 				(post_commit_ip - start_ip), abort_ip)
 
+/*
+ * Exit points of a rseq critical section consist of all instructions outside
+ * of the critical section where a critical section can either branch to or
+ * reach through the normal course of its execution. The abort IP and the
+ * post-commit IP are already part of the __rseq_table section and should not
+ * be explicitly defined as additional exit points. Knowing all exit points is
+ * useful to assist debuggers stepping over the critical section.
+ */
+#define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
+		".pushsection __rseq_exit_point_array, \"aw\"\n\t"	\
+		".long " __rseq_str(start_ip) ", 0x0, " __rseq_str(exit_ip) ", 0x0\n\t" \
+		".popsection\n\t"
+
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)		\
 		RSEQ_INJECT_ASM(1)					\
 		"movl $" __rseq_str(cs_label) ", " __rseq_str(rseq_cs) "\n\t"	\
@@ -569,6 +624,11 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -625,6 +685,11 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -683,6 +748,9 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -727,6 +795,11 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -788,6 +861,11 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -852,6 +930,12 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error3])
+#endif
 		/* Start rseq by storing table entry pointer into rseq_cs. */
 		RSEQ_ASM_STORE_RSEQ_CS(1, 3b, RSEQ_CS_OFFSET(%[rseq_abi]))
 		RSEQ_ASM_CMP_CPU_ID(cpu_id, RSEQ_CPU_ID_OFFSET(%[rseq_abi]), 4f)
@@ -920,6 +1004,11 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		"movl %[src], %[rseq_scratch0]\n\t"
 		"movl %[dst], %[rseq_scratch1]\n\t"
 		"movl %[len], %[rseq_scratch2]\n\t"
@@ -1027,6 +1116,11 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 
 	__asm__ __volatile__ goto (
 		RSEQ_ASM_DEFINE_TABLE(3, 1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
+#ifdef RSEQ_COMPARE_TWICE
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
+		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error2])
+#endif
 		"movl %[src], %[rseq_scratch0]\n\t"
 		"movl %[dst], %[rseq_scratch1]\n\t"
 		"movl %[len], %[rseq_scratch2]\n\t"
-- 
2.11.0

[RFC PATCH for 5.2 02/10] rseq/selftests: Introduce __rseq_cs_ptr_array, rename __rseq_table to __rseq_cs

[Mathieu Desnoyers]

The entries within __rseq_table are aligned on 32 bytes due to
linux/rseq.h struct rseq_cs uapi requirements, but the start of the
__rseq_table section is not guaranteed to be 32-byte aligned. It can
cause padding to be added at the start of the section, which makes it
hard to use as an array of items by debuggers.

Considering that __rseq_table does not really consist of a table due to
the presence of padding, rename this section to __rseq_cs.

Create a new __rseq_cs_ptr_array section which contains 64-bit packed
pointers to entries within the __rseq_cs section.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-arm.h   | 32 +++++++++++++++++--------------
 tools/testing/selftests/rseq/rseq-arm64.h |  9 ++++++---
 tools/testing/selftests/rseq/rseq-mips.h  | 32 +++++++++++++++++--------------
 tools/testing/selftests/rseq/rseq-ppc.h   | 22 +++++++++++++--------
 tools/testing/selftests/rseq/rseq-s390.h  | 18 +++++++++++------
 tools/testing/selftests/rseq/rseq-x86.h   | 19 ++++++++++++------
 6 files changed, 81 insertions(+), 51 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-arm.h b/tools/testing/selftests/rseq/rseq-arm.h
index 17e8d231943a..5f262c54364f 100644
--- a/tools/testing/selftests/rseq/rseq-arm.h
+++ b/tools/testing/selftests/rseq/rseq-arm.h
@@ -30,24 +30,28 @@ do {									\
 #include "rseq-skip.h"
 #else /* !RSEQ_SKIP_FASTPATH */
 
-#define __RSEQ_ASM_DEFINE_TABLE(version, flags,	start_ip,		\
+#define __RSEQ_ASM_DEFINE_TABLE(label, version, flags, start_ip,	\
 				post_commit_offset, abort_ip)		\
-		".pushsection __rseq_table, \"aw\"\n\t"			\
+		".pushsection __rseq_cs, \"aw\"\n\t"			\
 		".balign 32\n\t"					\
+		__rseq_str(label) ":\n\t"					\
 		".word " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) ", 0x0\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".word " __rseq_str(label) "b, 0x0\n\t"			\
 		".popsection\n\t"
 
-#define RSEQ_ASM_DEFINE_TABLE(start_ip, post_commit_ip, abort_ip)	\
-	__RSEQ_ASM_DEFINE_TABLE(0x0, 0x0, start_ip,			\
+#define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \
+	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,		\
 				(post_commit_ip - start_ip), abort_ip)
 
 /*
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
@@ -99,7 +103,7 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -166,7 +170,7 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -237,7 +241,7 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
 #endif
@@ -292,7 +296,7 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -367,7 +371,7 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -443,7 +447,7 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -527,7 +531,7 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -651,7 +655,7 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
index 2079f71e0ca2..b41a2a48e965 100644
--- a/tools/testing/selftests/rseq/rseq-arm64.h
+++ b/tools/testing/selftests/rseq/rseq-arm64.h
@@ -82,13 +82,16 @@ do {										\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags, start_ip,		\
 				post_commit_offset, abort_ip)			\
-	"	.pushsection	__rseq_table, \"aw\"\n"				\
+	"	.pushsection	__rseq_cs, \"aw\"\n"				\
 	"	.balign	32\n"							\
 	__rseq_str(label) ":\n"							\
 	"	.long	" __rseq_str(version) ", " __rseq_str(flags) "\n"	\
 	"	.quad	" __rseq_str(start_ip) ", "				\
 			  __rseq_str(post_commit_offset) ", "			\
 			  __rseq_str(abort_ip) "\n"				\
+	"	.popsection\n\t"						\
+	"	.pushsection __rseq_cs_ptr_array, \"aw\"\n"				\
+	"	.quad " __rseq_str(label) "b\n"					\
 	"	.popsection\n"
 
 #define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip)	\
@@ -99,8 +102,8 @@ do {										\
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)				\
diff --git a/tools/testing/selftests/rseq/rseq-mips.h b/tools/testing/selftests/rseq/rseq-mips.h
index 25d10ff54769..fe3eabcdcbe5 100644
--- a/tools/testing/selftests/rseq/rseq-mips.h
+++ b/tools/testing/selftests/rseq/rseq-mips.h
@@ -54,26 +54,30 @@ do {									\
 # error unsupported _MIPS_SZLONG
 #endif
 
-#define __RSEQ_ASM_DEFINE_TABLE(version, flags,	start_ip, \
+#define __RSEQ_ASM_DEFINE_TABLE(label, version, flags, start_ip, \
 				post_commit_offset, abort_ip) \
-		".pushsection __rseq_table, \"aw\"\n\t" \
+		".pushsection __rseq_cs, \"aw\"\n\t" \
 		".balign 32\n\t" \
+		__rseq_str(label) ":\n\t"					\
 		".word " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		LONG " " U32_U64_PAD(__rseq_str(start_ip)) "\n\t" \
 		LONG " " U32_U64_PAD(__rseq_str(post_commit_offset)) "\n\t" \
 		LONG " " U32_U64_PAD(__rseq_str(abort_ip)) "\n\t" \
+		".popsection\n\t" \
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t" \
+		LONG " " U32_U64_PAD(__rseq_str(label) "b") "\n\t" \
 		".popsection\n\t"
 
-#define RSEQ_ASM_DEFINE_TABLE(start_ip, post_commit_ip, abort_ip) \
-	__RSEQ_ASM_DEFINE_TABLE(0x0, 0x0, start_ip, \
+#define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \
+	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip, \
 				(post_commit_ip - start_ip), abort_ip)
 
 /*
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip) \
@@ -127,7 +131,7 @@ int rseq_cmpeqv_storev(intptr_t *v, intptr_t expect, intptr_t newv, int cpu)
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -192,7 +196,7 @@ int rseq_cmpnev_storeoffp_load(intptr_t *v, intptr_t expectnot,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -261,7 +265,7 @@ int rseq_addv(intptr_t *v, intptr_t count, int cpu)
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
 #endif
@@ -316,7 +320,7 @@ int rseq_cmpeqv_trystorev_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -389,7 +393,7 @@ int rseq_cmpeqv_trystorev_storev_release(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -463,7 +467,7 @@ int rseq_cmpeqv_cmpeqv_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -543,7 +547,7 @@ int rseq_cmpeqv_trymemcpy_storev(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
@@ -664,7 +668,7 @@ int rseq_cmpeqv_trymemcpy_storev_release(intptr_t *v, intptr_t expect,
 
 	rseq_workaround_gcc_asm_size_guess();
 	__asm__ __volatile__ goto (
-		RSEQ_ASM_DEFINE_TABLE(1f, 2f, 4f) /* start, commit, abort */
+		RSEQ_ASM_DEFINE_TABLE(9, 1f, 2f, 4f) /* start, commit, abort */
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[cmpfail])
 #ifdef RSEQ_COMPARE_TWICE
 		RSEQ_ASM_DEFINE_EXIT_POINT(1f, %l[error1])
diff --git a/tools/testing/selftests/rseq/rseq-ppc.h b/tools/testing/selftests/rseq/rseq-ppc.h
index 24f95649d71e..9df18487fa9f 100644
--- a/tools/testing/selftests/rseq/rseq-ppc.h
+++ b/tools/testing/selftests/rseq/rseq-ppc.h
@@ -33,8 +33,8 @@ do {									\
 #else /* !RSEQ_SKIP_FASTPATH */
 
 /*
- * The __rseq_table section can be used by debuggers to better handle
- * single-stepping through the restartable critical sections.
+ * The __rseq_cs_ptr_array and __rseq_cs sections can be used by debuggers to
+ * better handle single-stepping through the restartable critical sections.
  */
 
 #ifdef __PPC64__
@@ -46,11 +46,14 @@ do {									\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,				\
 			start_ip, post_commit_offset, abort_ip)			\
-		".pushsection __rseq_table, \"aw\"\n\t"				\
+		".pushsection __rseq_cs, \"aw\"\n\t"				\
 		".balign 32\n\t"						\
 		__rseq_str(label) ":\n\t"					\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t"	\
 		".quad " __rseq_str(start_ip) ", " __rseq_str(post_commit_offset) ", " __rseq_str(abort_ip) "\n\t" \
+		".popsection\n\t"						\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"			\
+		".quad " __rseq_str(label) "b\n\t"				\
 		".popsection\n\t"
 
 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs)			\
@@ -67,8 +70,8 @@ do {									\
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
@@ -85,20 +88,23 @@ do {									\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,				\
 			start_ip, post_commit_offset, abort_ip)			\
-		".pushsection __rseq_table, \"aw\"\n\t"				\
+		".pushsection __rseq_cs, \"aw\"\n\t"				\
 		".balign 32\n\t"						\
 		__rseq_str(label) ":\n\t"					\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t"	\
 		/* 32-bit only supported on BE */				\
 		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) "\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".long 0x0, " __rseq_str(label) "b\n\t"			\
 		".popsection\n\t"
 
 /*
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)				\
diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index b8b5b6f900af..fbb97815d71c 100644
--- a/tools/testing/selftests/rseq/rseq-s390.h
+++ b/tools/testing/selftests/rseq/rseq-s390.h
@@ -37,19 +37,22 @@ do {									\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
 				start_ip, post_commit_offset, abort_ip)	\
-		".pushsection __rseq_table, \"aw\"\n\t"			\
+		".pushsection __rseq_cs, \"aw\"\n\t"			\
 		".balign 32\n\t"					\
 		__rseq_str(label) ":\n\t"				\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".quad " __rseq_str(start_ip) ", " __rseq_str(post_commit_offset) ", " __rseq_str(abort_ip) "\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".quad " __rseq_str(label) "b\n\t"			\
 		".popsection\n\t"
 
 /*
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
@@ -61,19 +64,22 @@ do {									\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
 				start_ip, post_commit_offset, abort_ip)	\
-		".pushsection __rseq_table, \"aw\"\n\t"			\
+		".pushsection __rseq_cs, \"aw\"\n\t"			\
 		".balign 32\n\t"					\
 		__rseq_str(label) ":\n\t"				\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".long 0x0, " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) "\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".long 0x0, " __rseq_str(label) "b\n\t"			\
 		".popsection\n\t"
 
 /*
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h
index 0668608d3674..03095236f6fa 100644
--- a/tools/testing/selftests/rseq/rseq-x86.h
+++ b/tools/testing/selftests/rseq/rseq-x86.h
@@ -47,13 +47,17 @@ do {									\
 
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
 				start_ip, post_commit_offset, abort_ip)	\
-		".pushsection __rseq_table, \"aw\"\n\t"			\
+		".pushsection __rseq_cs, \"aw\"\n\t"			\
 		".balign 32\n\t"					\
 		__rseq_str(label) ":\n\t"				\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".quad " __rseq_str(start_ip) ", " __rseq_str(post_commit_offset) ", " __rseq_str(abort_ip) "\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".quad " __rseq_str(label) "b\n\t"			\
 		".popsection\n\t"
 
+
 #define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \
 	__RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip,		\
 				(post_commit_ip - start_ip), abort_ip)
@@ -62,8 +66,8 @@ do {									\
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
@@ -566,11 +570,14 @@ do {									\
  */
 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags,			\
 				start_ip, post_commit_offset, abort_ip)	\
-		".pushsection __rseq_table, \"aw\"\n\t"			\
+		".pushsection __rseq_cs, \"aw\"\n\t"			\
 		".balign 32\n\t"					\
 		__rseq_str(label) ":\n\t"				\
 		".long " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".long " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) ", 0x0\n\t" \
+		".popsection\n\t"					\
+		".pushsection __rseq_cs_ptr_array, \"aw\"\n\t"		\
+		".long " __rseq_str(label) "b, 0x0\n\t"			\
 		".popsection\n\t"
 
 #define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \
@@ -581,8 +588,8 @@ do {									\
  * Exit points of a rseq critical section consist of all instructions outside
  * of the critical section where a critical section can either branch to or
  * reach through the normal course of its execution. The abort IP and the
- * post-commit IP are already part of the __rseq_table section and should not
- * be explicitly defined as additional exit points. Knowing all exit points is
+ * post-commit IP are already part of the __rseq_cs section and should not be
+ * explicitly defined as additional exit points. Knowing all exit points is
  * useful to assist debuggers stepping over the critical section.
  */
 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip)			\
-- 
2.11.0

[RFC PATCH for 5.2 03/10] rseq/selftests: Use __rseq_handled symbol to coexist with glibc

[Mathieu Desnoyers]

In order to integrate rseq into user-space applications, expose a
__rseq_handled symbol so many rseq users can be linked into the same
application (e.g. librseq and glibc).

The __rseq_refcount TLS variable is static to the librseq library. It
ensures that rseq syscall registration/unregistration happens only for
the most early/late caller to rseq_{,un}register_current_thread for each
thread, thus ensuring that rseq is registered across the lifetime of all
rseq users for a given thread.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Carlos O'Donell <carlos@redhat.com>
CC: Florian Weimer <fweimer@redhat.com>
CC: Joseph Myers <joseph@codesourcery.com>
CC: Szabolcs Nagy <szabolcs.nagy@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ben Maurer <bmaurer@fb.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Paul Turner <pjt@google.com>
CC: linux-api@vger.kernel.org
---
 tools/testing/selftests/rseq/rseq.c | 55 +++++++++++++++++++++++++++++++------
 tools/testing/selftests/rseq/rseq.h |  1 +
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..d44cc17ad929 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -25,18 +25,27 @@
 #include <syscall.h>
 #include <assert.h>
 #include <signal.h>
+#include <limits.h>
 
 #include "rseq.h"
 
 #define ARRAY_SIZE(arr)	(sizeof(arr) / sizeof((arr)[0]))
 
-__attribute__((tls_model("initial-exec"))) __thread
-volatile struct rseq __rseq_abi = {
+__thread volatile struct rseq __rseq_abi = {
 	.cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
 };
 
-static __attribute__((tls_model("initial-exec"))) __thread
-volatile int refcount;
+/*
+ * Shared with other libraries. This library may take rseq ownership if it is
+ * still 0 when executing the library constructor. Set to 1 by library
+ * constructor when handling rseq. Set to 0 in destructor if handling rseq.
+ */
+int __rseq_handled;
+
+/* Whether this library have ownership of rseq registration. */
+static int rseq_ownership;
+
+static __thread volatile uint32_t __rseq_refcount;
 
 static void signal_off_save(sigset_t *oldset)
 {
@@ -69,8 +78,14 @@ int rseq_register_current_thread(void)
 	int rc, ret = 0;
 	sigset_t oldset;
 
+	if (!rseq_ownership)
+		return 0;
 	signal_off_save(&oldset);
-	if (refcount++)
+	if (__rseq_refcount == UINT_MAX) {
+		ret = -1;
+		goto end;
+	}
+	if (__rseq_refcount++)
 		goto end;
 	rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
 	if (!rc) {
@@ -78,9 +93,9 @@ int rseq_register_current_thread(void)
 		goto end;
 	}
 	if (errno != EBUSY)
-		__rseq_abi.cpu_id = -2;
+		__rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
 	ret = -1;
-	refcount--;
+	__rseq_lib_abi.refcount--;
 end:
 	signal_restore(oldset);
 	return ret;
@@ -91,13 +106,20 @@ int rseq_unregister_current_thread(void)
 	int rc, ret = 0;
 	sigset_t oldset;
 
+	if (!rseq_ownership)
+		return 0;
 	signal_off_save(&oldset);
-	if (--refcount)
+	if (!__rseq_refcount) {
+		ret = -1;
+		goto end;
+	}
+	if (--__rseq_refcount)
 		goto end;
 	rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
 		      RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
 	if (!rc)
 		goto end;
+	__rseq_refcount = 1;
 	ret = -1;
 end:
 	signal_restore(oldset);
@@ -115,3 +137,20 @@ int32_t rseq_fallback_current_cpu(void)
 	}
 	return cpu;
 }
+
+void __attribute__((constructor)) rseq_init(void)
+{
+	/* Check whether rseq is handled by another library. */
+	if (__rseq_handled)
+		return;
+	__rseq_handled = 1;
+	rseq_ownership = 1;
+}
+
+void __attribute__((destructor)) rseq_fini(void)
+{
+	if (!rseq_ownership)
+		return;
+	__rseq_handled = 0;
+	rseq_ownership = 0;
+}
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index c72eb70f9b52..26348e2c44f3 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -45,6 +45,7 @@
 #endif
 
 extern __thread volatile struct rseq __rseq_abi;
+extern int __rseq_handled;
 
 #define rseq_likely(x)		__builtin_expect(!!(x), 1)
 #define rseq_unlikely(x)	__builtin_expect(!!(x), 0)
-- 
2.11.0

[RFC PATCH for 5.2 04/10] rseq/selftests: s390: use jg instruction for jumps outside of the asm

[Mathieu Desnoyers]

The branch target range of the "j" instruction is 64K, which is not
enough for the general case.

Suggested-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-s390.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index fbb97815d71c..7c4f3a70b6c7 100644
--- a/tools/testing/selftests/rseq/rseq-s390.h
+++ b/tools/testing/selftests/rseq/rseq-s390.h
@@ -117,14 +117,14 @@ do {									\
 		".long " __rseq_str(RSEQ_SIG) "\n\t"			\
 		__rseq_str(label) ":\n\t"				\
 		teardown						\
-		"j %l[" __rseq_str(abort_label) "]\n\t"			\
+		"jg %l[" __rseq_str(abort_label) "]\n\t"		\
 		".popsection\n\t"
 
 #define RSEQ_ASM_DEFINE_CMPFAIL(label, teardown, cmpfail_label)		\
 		".pushsection __rseq_failure, \"ax\"\n\t"		\
 		__rseq_str(label) ":\n\t"				\
 		teardown						\
-		"j %l[" __rseq_str(cmpfail_label) "]\n\t"		\
+		"jg %l[" __rseq_str(cmpfail_label) "]\n\t"		\
 		".popsection\n\t"
 
 static inline __attribute__((always_inline))
-- 
2.11.0

[RFC PATCH for 5.2 05/10] rseq/selftests: x86: use ud1 instruction as RSEQ_SIG opcode

[Mathieu Desnoyers]

Use ud1 as the guard instruction for the restartable sequence abort
handler. Its benefit compared to nopl is to trap execution if the
program ends up trying to execute it by mistake, which makes debugging
easier.

The 4-byte signature per se is unchanged (it is the instruction
operand). Only the opcode is changed from nopl to ud1.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-x86.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h
index 03095236f6fa..b2da6004fe30 100644
--- a/tools/testing/selftests/rseq/rseq-x86.h
+++ b/tools/testing/selftests/rseq/rseq-x86.h
@@ -7,6 +7,13 @@
 
 #include <stdint.h>
 
+/*
+ * RSEQ_SIG is used with the following reserved undefined instructions, which
+ * trap in user-space:
+ *
+ * x86-32:    0f b9 3d 53 30 05 53      ud1    0x53053053,%edi
+ * x86-64:    0f b9 3d 53 30 05 53      ud1    0x53053053(%rip),%edi
+ */
 #define RSEQ_SIG	0x53053053
 
 /*
@@ -88,8 +95,8 @@ do {									\
 
 #define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label)		\
 		".pushsection __rseq_failure, \"ax\"\n\t"		\
-		/* Disassembler-friendly signature: nopl <sig>(%rip). */\
-		".byte 0x0f, 0x1f, 0x05\n\t"				\
+		/* Disassembler-friendly signature: ud1 <sig>(%rip),%edi. */ \
+		".byte 0x0f, 0xb9, 0x3d\n\t"				\
 		".long " __rseq_str(RSEQ_SIG) "\n\t"			\
 		__rseq_str(label) ":\n\t"				\
 		teardown						\
@@ -609,8 +616,8 @@ do {									\
 
 #define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label)		\
 		".pushsection __rseq_failure, \"ax\"\n\t"		\
-		/* Disassembler-friendly signature: nopl <sig>. */	\
-		".byte 0x0f, 0x1f, 0x05\n\t"				\
+		/* Disassembler-friendly signature: ud1 <sig>,%edi. */	\
+		".byte 0x0f, 0xb9, 0x3d\n\t"				\
 		".long " __rseq_str(RSEQ_SIG) "\n\t"			\
 		__rseq_str(label) ":\n\t"				\
 		teardown						\
-- 
2.11.0

[RFC PATCH for 5.2 06/10] rseq/selftests: s390: use trap4 for RSEQ_SIG

[Mathieu Desnoyers]

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Use trap4 as the guard instruction for the restartable sequence abort
handler.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 tools/testing/selftests/rseq/rseq-s390.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index 7c4f3a70b6c7..1d05c5187ae6 100644
--- a/tools/testing/selftests/rseq/rseq-s390.h
+++ b/tools/testing/selftests/rseq/rseq-s390.h
@@ -1,6 +1,13 @@
 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */
 
-#define RSEQ_SIG	0x53053053
+/*
+ * RSEQ_SIG uses the trap4 instruction. As Linux does not make use of the
+ * access-register mode nor the linkage stack this instruction will always
+ * cause a special-operation exception (the trap-enabled bit in the DUCT
+ * is and will stay 0). The instruction pattern is
+ *	b2 ff 0f ff	trap4   4095(%r0)
+ */
+#define RSEQ_SIG	0xB2FF0FFF
 
 #define rseq_smp_mb()	__asm__ __volatile__ ("bcr 15,0" ::: "memory")
 #define rseq_smp_rmb()	rseq_smp_mb()
-- 
2.11.0

[RFC PATCH for 5.2 07/10] rseq/selftests: arm: use udf instruction for RSEQ_SIG

[Mathieu Desnoyers]

Use udf as the guard instruction for the restartable sequence abort
handler.

Previously, the chosen signature was not a valid instruction, based
on the assumption that it could always sit in a literal pool. However,
there are compilation environments in which literal pools are not
availble, for instance execute-only code. Therefore, we need to
choose a signature value that is also a valid instruction.

Handle compiling with -mbig-endian on ARMv6+, which generates binaries
with mixed code vs data endianness (little endian code, big endian
data).

Else mismatch between code endianness for the generated signatures and
data endianness for the RSEQ_SIG parameter passed to the rseq
registration will trigger application segmentation faults when the
kernel try to abort rseq critical sections.

Prior to ARMv6, -mbig-endian generates big-endian code and data, so
endianness should not be reversed in that case.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-arm.h | 52 +++++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-arm.h b/tools/testing/selftests/rseq/rseq-arm.h
index 5f262c54364f..e8ccfc37d685 100644
--- a/tools/testing/selftests/rseq/rseq-arm.h
+++ b/tools/testing/selftests/rseq/rseq-arm.h
@@ -5,7 +5,54 @@
  * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  */
 
-#define RSEQ_SIG	0x53053053
+/*
+ * RSEQ_SIG uses the udf A32 instruction with an uncommon immediate operand
+ * value 0x5de3. This traps if user-space reaches this instruction by mistake,
+ * and the uncommon operand ensures the kernel does not move the instruction
+ * pointer to attacker-controlled code on rseq abort.
+ *
+ * The instruction pattern in the A32 instruction set is:
+ *
+ * e7f5def3    udf    #24035    ; 0x5de3
+ *
+ * This translates to the following instruction pattern in the T16 instruction
+ * set:
+ *
+ * little endian:
+ * def3        udf    #243      ; 0xf3
+ * e7f5        b.n    <7f5>
+ *
+ * pre-ARMv6 big endian code:
+ * e7f5        b.n    <7f5>
+ * def3        udf    #243      ; 0xf3
+ *
+ * ARMv6+ -mbig-endian generates mixed endianness code vs data: little-endian
+ * code and big-endian data. Ensure the RSEQ_SIG data signature matches code
+ * endianness. Prior to ARMv6, -mbig-endian generates big-endian code and data
+ * (which match), so there is no need to reverse the endianness of the data
+ * representation of the signature. However, the choice between BE32 and BE8
+ * is done by the linker, so we cannot know whether code and data endianness
+ * will be mixed before the linker is invoked.
+ */
+
+#define RSEQ_SIG_CODE	0xe7f5def3
+
+#ifndef __ASSEMBLER__
+
+#define RSEQ_SIG_DATA							\
+	({								\
+		int sig;						\
+		asm volatile (  "b 2f\n\t"				\
+				"1: .inst " __rseq_str(RSEQ_SIG_CODE) "\n\t" \
+				"2:\n\t"				\
+				"ldr %[sig], 1b\n\t"			\
+				: [sig] "=r" (sig));			\
+		sig;							\
+	})
+
+#define RSEQ_SIG	RSEQ_SIG_DATA
+
+#endif
 
 #define rseq_smp_mb()	__asm__ __volatile__ ("dmb" ::: "memory", "cc")
 #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb" ::: "memory", "cc")
@@ -78,7 +125,8 @@ do {									\
 		__rseq_str(table_label) ":\n\t"				\
 		".word " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \
 		".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) ", 0x0\n\t" \
-		".word " __rseq_str(RSEQ_SIG) "\n\t"			\
+		".arm\n\t"						\
+		".inst " __rseq_str(RSEQ_SIG_CODE) "\n\t"		\
 		__rseq_str(label) ":\n\t"				\
 		teardown						\
 		"b %l[" __rseq_str(abort_label) "]\n\t"
-- 
2.11.0

[RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mathieu Desnoyers]

Handle compiling with -mbig-endian on aarch64, which generates binaries
with mixed code vs data endianness (little endian code, big endian
data).

Else mismatch between code endianness for the generated signatures and
data endianness for the RSEQ_SIG parameter passed to the rseq
registration will trigger application segmentation faults when the
kernel try to abort rseq critical sections.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Joel Fernandes <joelaf@google.com>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Shuah Khan <shuah@kernel.org>
CC: Andi Kleen <andi@firstfloor.org>
CC: linux-kselftest@vger.kernel.org
CC: "H . Peter Anvin" <hpa@zytor.com>
CC: Chris Lameter <cl@linux.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
CC: Paul Turner <pjt@google.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Maurer <bmaurer@fb.com>
CC: linux-api@vger.kernel.org
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/rseq-arm64.h | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
index b41a2a48e965..200dae9e4208 100644
--- a/tools/testing/selftests/rseq/rseq-arm64.h
+++ b/tools/testing/selftests/rseq/rseq-arm64.h
@@ -6,7 +6,20 @@
  * (C) Copyright 2018 - Will Deacon <will.deacon@arm.com>
  */
 
-#define RSEQ_SIG	0xd428bc00	/* BRK #0x45E0 */
+/*
+ * aarch64 -mbig-endian generates mixed endianness code vs data:
+ * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
+ * matches code endianness.
+ */
+#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
+
+#ifdef __AARCH64EB__
+#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
+#else
+#define RSEQ_SIG_DATA	RSEQ_SIG_CODE
+#endif
+
+#define RSEQ_SIG	RSEQ_SIG_DATA
 
 #define rseq_smp_mb()	__asm__ __volatile__ ("dmb ish" ::: "memory")
 #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb ishld" ::: "memory")
@@ -121,7 +134,7 @@ do {										\
 
 #define RSEQ_ASM_DEFINE_ABORT(label, abort_label)				\
 	"	b	222f\n"							\
-	"	.inst 	"	__rseq_str(RSEQ_SIG) "\n"			\
+	"	.inst 	"	__rseq_str(RSEQ_SIG_CODE) "\n"			\
 	__rseq_str(label) ":\n"							\
 	"	b	%l[" __rseq_str(abort_label) "]\n"			\
 	"222:\n"
-- 
2.11.0

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mark Rutland]

On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> Handle compiling with -mbig-endian on aarch64, which generates binaries
> with mixed code vs data endianness (little endian code, big endian
> data).
> 
> Else mismatch between code endianness for the generated signatures and
> data endianness for the RSEQ_SIG parameter passed to the rseq
> registration will trigger application segmentation faults when the
> kernel try to abort rseq critical sections.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Joel Fernandes <joelaf@google.com>
> CC: Catalin Marinas <catalin.marinas@arm.com>
> CC: Dave Watson <davejwatson@fb.com>
> CC: Will Deacon <will.deacon@arm.com>
> CC: Shuah Khan <shuah@kernel.org>
> CC: Andi Kleen <andi@firstfloor.org>
> CC: linux-kselftest@vger.kernel.org
> CC: "H . Peter Anvin" <hpa@zytor.com>
> CC: Chris Lameter <cl@linux.com>
> CC: Russell King <linux@arm.linux.org.uk>
> CC: Michael Kerrisk <mtk.manpages@gmail.com>
> CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
> CC: Paul Turner <pjt@google.com>
> CC: Boqun Feng <boqun.feng@gmail.com>
> CC: Josh Triplett <josh@joshtriplett.org>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ben Maurer <bmaurer@fb.com>
> CC: linux-api@vger.kernel.org
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> ---
>  tools/testing/selftests/rseq/rseq-arm64.h | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
> index b41a2a48e965..200dae9e4208 100644
> --- a/tools/testing/selftests/rseq/rseq-arm64.h
> +++ b/tools/testing/selftests/rseq/rseq-arm64.h
> @@ -6,7 +6,20 @@
>   * (C) Copyright 2018 - Will Deacon <will.deacon@arm.com>
>   */
>  
> -#define RSEQ_SIG	0xd428bc00	/* BRK #0x45E0 */
> +/*
> + * aarch64 -mbig-endian generates mixed endianness code vs data:
> + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> + * matches code endianness.
> + */
> +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> +
> +#ifdef __AARCH64EB__
> +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
> +#else
> +#define RSEQ_SIG_DATA	RSEQ_SIG_CODE
> +#endif
> +
> +#define RSEQ_SIG	RSEQ_SIG_DATA
>  
>  #define rseq_smp_mb()	__asm__ __volatile__ ("dmb ish" ::: "memory")
>  #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb ishld" ::: "memory")
> @@ -121,7 +134,7 @@ do {										\
>  
>  #define RSEQ_ASM_DEFINE_ABORT(label, abort_label)				\
>  	"	b	222f\n"							\
> -	"	.inst 	"	__rseq_str(RSEQ_SIG) "\n"			\
> +	"	.inst 	"	__rseq_str(RSEQ_SIG_CODE) "\n"			\

I don't think this is right; the .inst directive _should_ emit the value
in the instruction stream endianness (i.e. LE, regardless of the data
endianness).

That's certainly the case with the kernel.org crosstool GCC:

[mark@lakrids:/mnt/data/tests/inst-test]% cat test.c                               
void func(void)
{
        asm volatile(".inst 0xd4000001");
}
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -c test.c
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o

test.o:     file format elf64-littleaarch64


Disassembly of section .text:

0000000000000000 <func>:
   0:   d4000001        svc     #0x0
   4:   d503201f        nop
   8:   d65f03c0        ret
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -mbig-endian -c test.c
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o         

test.o:     file format elf64-bigaarch64


Disassembly of section .text:

0000000000000000 <func>:
   0:   d4000001        svc     #0x0
   4:   d503201f        nop
   8:   d65f03c0        ret



Have you tested this? Is there some toolchain that doesn't get this
right?

Thanks,
Mark.

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Will Deacon]

On Wed, Apr 24, 2019 at 05:40:33PM +0100, Mark Rutland wrote:
> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> > Handle compiling with -mbig-endian on aarch64, which generates binaries
> > with mixed code vs data endianness (little endian code, big endian
> > data).
> > 
> > Else mismatch between code endianness for the generated signatures and
> > data endianness for the RSEQ_SIG parameter passed to the rseq
> > registration will trigger application segmentation faults when the
> > kernel try to abort rseq critical sections.
> > 
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > CC: Peter Zijlstra <peterz@infradead.org>
> > CC: Thomas Gleixner <tglx@linutronix.de>
> > CC: Joel Fernandes <joelaf@google.com>
> > CC: Catalin Marinas <catalin.marinas@arm.com>
> > CC: Dave Watson <davejwatson@fb.com>
> > CC: Will Deacon <will.deacon@arm.com>
> > CC: Shuah Khan <shuah@kernel.org>
> > CC: Andi Kleen <andi@firstfloor.org>
> > CC: linux-kselftest@vger.kernel.org
> > CC: "H . Peter Anvin" <hpa@zytor.com>
> > CC: Chris Lameter <cl@linux.com>
> > CC: Russell King <linux@arm.linux.org.uk>
> > CC: Michael Kerrisk <mtk.manpages@gmail.com>
> > CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
> > CC: Paul Turner <pjt@google.com>
> > CC: Boqun Feng <boqun.feng@gmail.com>
> > CC: Josh Triplett <josh@joshtriplett.org>
> > CC: Steven Rostedt <rostedt@goodmis.org>
> > CC: Ben Maurer <bmaurer@fb.com>
> > CC: linux-api@vger.kernel.org
> > CC: Andy Lutomirski <luto@amacapital.net>
> > CC: Andrew Morton <akpm@linux-foundation.org>
> > CC: Linus Torvalds <torvalds@linux-foundation.org>
> > ---
> >  tools/testing/selftests/rseq/rseq-arm64.h | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
> > index b41a2a48e965..200dae9e4208 100644
> > --- a/tools/testing/selftests/rseq/rseq-arm64.h
> > +++ b/tools/testing/selftests/rseq/rseq-arm64.h
> > @@ -6,7 +6,20 @@
> >   * (C) Copyright 2018 - Will Deacon <will.deacon@arm.com>
> >   */
> >  
> > -#define RSEQ_SIG	0xd428bc00	/* BRK #0x45E0 */
> > +/*
> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> > + * matches code endianness.
> > + */
> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> > +
> > +#ifdef __AARCH64EB__
> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
> > +#else
> > +#define RSEQ_SIG_DATA	RSEQ_SIG_CODE
> > +#endif
> > +
> > +#define RSEQ_SIG	RSEQ_SIG_DATA
> >  
> >  #define rseq_smp_mb()	__asm__ __volatile__ ("dmb ish" ::: "memory")
> >  #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb ishld" ::: "memory")
> > @@ -121,7 +134,7 @@ do {										\
> >  
> >  #define RSEQ_ASM_DEFINE_ABORT(label, abort_label)				\
> >  	"	b	222f\n"							\
> > -	"	.inst 	"	__rseq_str(RSEQ_SIG) "\n"			\
> > +	"	.inst 	"	__rseq_str(RSEQ_SIG_CODE) "\n"			\
> 
> I don't think this is right; the .inst directive _should_ emit the value
> in the instruction stream endianness (i.e. LE, regardless of the data
> endianness).
> 
> That's certainly the case with the kernel.org crosstool GCC:
> 
> [mark@lakrids:/mnt/data/tests/inst-test]% cat test.c                               
> void func(void)
> {
>         asm volatile(".inst 0xd4000001");
> }
> [mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -c test.c
> [mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o
> 
> test.o:     file format elf64-littleaarch64
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <func>:
>    0:   d4000001        svc     #0x0
>    4:   d503201f        nop
>    8:   d65f03c0        ret
> [mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -mbig-endian -c test.c
> [mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o         
> 
> test.o:     file format elf64-bigaarch64
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <func>:
>    0:   d4000001        svc     #0x0
>    4:   d503201f        nop
>    8:   d65f03c0        ret
> 
> 
> 
> Have you tested this? Is there some toolchain that doesn't get this
> right?

I think that the issue is that the kernel loads the thing to check the
signature. RSEQ_SIG_CODE isn't byte-swapped explicitly and is used with
.inst. RSEG_SIG_DATA is byte-swapped to ensure that the value passed into
the syscall is consistent with what the kernel will load.

But yeah, I've just spent the last ten minutes confusing myself with this.

Will

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mark Rutland]

On Wed, Apr 24, 2019 at 05:40:33PM +0100, Mark Rutland wrote:
> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> > +/*
> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> > + * matches code endianness.
> > + */
> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> > +
> > +#ifdef __AARCH64EB__
> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
> > +#else
> > +#define RSEQ_SIG_DATA	RSEQ_SIG_CODE
> > +#endif
> > +
> > +#define RSEQ_SIG	RSEQ_SIG_DATA
> >  
> >  #define rseq_smp_mb()	__asm__ __volatile__ ("dmb ish" ::: "memory")
> >  #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb ishld" ::: "memory")
> > @@ -121,7 +134,7 @@ do {										\
> >  
> >  #define RSEQ_ASM_DEFINE_ABORT(label, abort_label)				\
> >  	"	b	222f\n"							\
> > -	"	.inst 	"	__rseq_str(RSEQ_SIG) "\n"			\
> > +	"	.inst 	"	__rseq_str(RSEQ_SIG_CODE) "\n"			\
> 
> I don't think this is right; the .inst directive _should_ emit the value
> in the instruction stream endianness (i.e. LE, regardless of the data
> endianness).

Now I see the RSEQ_CODE value isn't endian-swapped as teh RSEQ_DATA
value is, so the code above is fine.

Sory for the noise.

Thanks,
Mark.

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Will Deacon]

On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> Handle compiling with -mbig-endian on aarch64, which generates binaries
> with mixed code vs data endianness (little endian code, big endian
> data).
> 
> Else mismatch between code endianness for the generated signatures and
> data endianness for the RSEQ_SIG parameter passed to the rseq
> registration will trigger application segmentation faults when the
> kernel try to abort rseq critical sections.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Joel Fernandes <joelaf@google.com>
> CC: Catalin Marinas <catalin.marinas@arm.com>
> CC: Dave Watson <davejwatson@fb.com>
> CC: Will Deacon <will.deacon@arm.com>
> CC: Shuah Khan <shuah@kernel.org>
> CC: Andi Kleen <andi@firstfloor.org>
> CC: linux-kselftest@vger.kernel.org
> CC: "H . Peter Anvin" <hpa@zytor.com>
> CC: Chris Lameter <cl@linux.com>
> CC: Russell King <linux@arm.linux.org.uk>
> CC: Michael Kerrisk <mtk.manpages@gmail.com>
> CC: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
> CC: Paul Turner <pjt@google.com>
> CC: Boqun Feng <boqun.feng@gmail.com>
> CC: Josh Triplett <josh@joshtriplett.org>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ben Maurer <bmaurer@fb.com>
> CC: linux-api@vger.kernel.org
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> ---
>  tools/testing/selftests/rseq/rseq-arm64.h | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
> index b41a2a48e965..200dae9e4208 100644
> --- a/tools/testing/selftests/rseq/rseq-arm64.h
> +++ b/tools/testing/selftests/rseq/rseq-arm64.h
> @@ -6,7 +6,20 @@
>   * (C) Copyright 2018 - Will Deacon <will.deacon@arm.com>
>   */
>  
> -#define RSEQ_SIG	0xd428bc00	/* BRK #0x45E0 */
> +/*
> + * aarch64 -mbig-endian generates mixed endianness code vs data:
> + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> + * matches code endianness.
> + */
> +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> +
> +#ifdef __AARCH64EB__
> +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */

It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,
but either way:

Acked-by: Will Deacon <will.deacon@arm.com>

Will

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mark Rutland]

On Wed, Apr 24, 2019 at 05:45:38PM +0100, Will Deacon wrote:
> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> > +/*
> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> > + * matches code endianness.
> > + */
> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> > +
> > +#ifdef __AARCH64EB__
> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
> 
> It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,

If possible, marginally neater than that would be using
le32_to_cpu(RSEQ_SIG_CODE), without any ifdeffery necessary.

It looks like that's defined in tools/include/linux/kernel.h, but I'm
not sure if that gets pulled into your include path.

Thanks,
Mark.

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mathieu Desnoyers]

----- On Apr 24, 2019, at 12:51 PM, Mark Rutland mark.rutland@arm.com wrote:

> On Wed, Apr 24, 2019 at 05:45:38PM +0100, Will Deacon wrote:
>> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
>> > +/*
>> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
>> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
>> > + * matches code endianness.
>> > + */
>> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
>> > +
>> > +#ifdef __AARCH64EB__
>> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
>> 
>> It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,
> 
> If possible, marginally neater than that would be using
> le32_to_cpu(RSEQ_SIG_CODE), without any ifdeffery necessary.
> 
> It looks like that's defined in tools/include/linux/kernel.h, but I'm
> not sure if that gets pulled into your include path.

Considering that those RSEQ_SIG* define will end up in public bits/rseq.h
headers within glibc, I'm tempted to keep the amount of dependencies on
external headers to a minimum, if it's OK with you.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Mathieu Desnoyers]

----- On Apr 24, 2019, at 1:00 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On Apr 24, 2019, at 12:51 PM, Mark Rutland mark.rutland@arm.com wrote:
> 
>> On Wed, Apr 24, 2019 at 05:45:38PM +0100, Will Deacon wrote:
>>> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
>>> > +/*
>>> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
>>> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
>>> > + * matches code endianness.
>>> > + */
>>> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
>>> > +
>>> > +#ifdef __AARCH64EB__
>>> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
>>> 
>>> It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,
>> 
>> If possible, marginally neater than that would be using
>> le32_to_cpu(RSEQ_SIG_CODE), without any ifdeffery necessary.
>> 
>> It looks like that's defined in tools/include/linux/kernel.h, but I'm
>> not sure if that gets pulled into your include path.
> 
> Considering that those RSEQ_SIG* define will end up in public bits/rseq.h
> headers within glibc, I'm tempted to keep the amount of dependencies on
> external headers to a minimum, if it's OK with you.

Also, I'm not sure the le32_to_cpu() approach would work in __ASSEMBLER__
builds.

Thanks,

Mathieu

> 
> Thanks,
> 
> Mathieu
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

[RFC PATCH for 5.2 09/10] rseq/selftests: powerpc code signature: generate valid instructions

[Mathieu Desnoyers]

Use "twui" as the guard instruction for the restartable sequence abort
handler.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Alan Modra <amodra@gmail.com>
CC: linuxppc-dev@lists.ozlabs.org
---
 tools/testing/selftests/rseq/rseq-ppc.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rseq/rseq-ppc.h b/tools/testing/selftests/rseq/rseq-ppc.h
index 9df18487fa9f..76be90196fe4 100644
--- a/tools/testing/selftests/rseq/rseq-ppc.h
+++ b/tools/testing/selftests/rseq/rseq-ppc.h
@@ -6,7 +6,15 @@
  * (C) Copyright 2016-2018 - Boqun Feng <boqun.feng@gmail.com>
  */
 
-#define RSEQ_SIG	0x53053053
+/*
+ * RSEQ_SIG is used with the following trap instruction:
+ *
+ * powerpc-be:    0f e5 00 0b           twui   r5,11
+ * powerpc64-le:  0b 00 e5 0f           twui   r5,11
+ * powerpc64-be:  0f e5 00 0b           twui   r5,11
+ */
+
+#define RSEQ_SIG	0x0fe5000b
 
 #define rseq_smp_mb()		__asm__ __volatile__ ("sync"	::: "memory", "cc")
 #define rseq_smp_lwsync()	__asm__ __volatile__ ("lwsync"	::: "memory", "cc")
-- 
2.11.0

[RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Mathieu Desnoyers]

Use break as guard instruction for the restartable sequence abort
handler.

Previously, the chosen signature was simply data, based on the
assumption that it could always sit in a literal pool. However,
some compilation environments favor disabling literal pool. Therefore,
ensure the signature is a valid uncommon trap instruction.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Paul Burton <paul.burton@mips.com>
CC: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
---
 tools/testing/selftests/rseq/rseq-mips.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rseq/rseq-mips.h b/tools/testing/selftests/rseq/rseq-mips.h
index fe3eabcdcbe5..eb53a6adfbbb 100644
--- a/tools/testing/selftests/rseq/rseq-mips.h
+++ b/tools/testing/selftests/rseq/rseq-mips.h
@@ -7,7 +7,11 @@
  * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  */
 
-#define RSEQ_SIG	0x53053053
+/*
+ * RSEQ_SIG uses the break instruction. The instruction pattern is
+ *	0350000d        break    0x350
+ */
+#define RSEQ_SIG	0x0350000d
 
 #define rseq_smp_mb()	__asm__ __volatile__ ("sync" ::: "memory")
 #define rseq_smp_rmb()	rseq_smp_mb()
-- 
2.11.0

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Paul Burton]

Hi Mathieu,

On Wed, Apr 24, 2019 at 11:25:02AM -0400, Mathieu Desnoyers wrote:
> diff --git a/tools/testing/selftests/rseq/rseq-mips.h b/tools/testing/selftests/rseq/rseq-mips.h
> index fe3eabcdcbe5..eb53a6adfbbb 100644
> --- a/tools/testing/selftests/rseq/rseq-mips.h
> +++ b/tools/testing/selftests/rseq/rseq-mips.h
> @@ -7,7 +7,11 @@
>   * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>   */
>  
> -#define RSEQ_SIG	0x53053053
> +/*
> + * RSEQ_SIG uses the break instruction. The instruction pattern is
> + *	0350000d        break    0x350
> + */
> +#define RSEQ_SIG	0x0350000d

My apologies for taking a while to get back to you on the various ISAs &
endian issues here, but I think we'll want this to be something like:

#if defined(__nanomips__)
# ifdef __MIPSEL__
#  define RSEQ_SIG	0x03500010
# else
#  define RSEQ_SIG	0x00100350
# endif
#elif defined(__mips_micromips)
# ifdef __MIPSEL__
#  define RSEQ_SIG	0xd4070000
# else
#  define RSEQ_SIG	0x0000d407
# endif
#else
# define RSEQ_SIG	0x0350000d
#endif

For plain old MIPS the .word directive will be fine endian-wise, but for
microMIPS & nanoMIPS we need to take into account that the instruction
stream is encoded as 16b halfwords & swap those accordingly for little
endian.

Thanks,
    Paul

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Mathieu Desnoyers]

----- On Apr 24, 2019, at 6:06 PM, Paul Burton paul.burton@mips.com wrote:

> Hi Mathieu,
> 
> On Wed, Apr 24, 2019 at 11:25:02AM -0400, Mathieu Desnoyers wrote:
>> diff --git a/tools/testing/selftests/rseq/rseq-mips.h
>> b/tools/testing/selftests/rseq/rseq-mips.h
>> index fe3eabcdcbe5..eb53a6adfbbb 100644
>> --- a/tools/testing/selftests/rseq/rseq-mips.h
>> +++ b/tools/testing/selftests/rseq/rseq-mips.h
>> @@ -7,7 +7,11 @@
>>   * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>   */
>>  
>> -#define RSEQ_SIG	0x53053053
>> +/*
>> + * RSEQ_SIG uses the break instruction. The instruction pattern is
>> + *	0350000d        break    0x350
>> + */
>> +#define RSEQ_SIG	0x0350000d
> 
> My apologies for taking a while to get back to you on the various ISAs &
> endian issues here, but I think we'll want this to be something like:
> 
> #if defined(__nanomips__)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0x03500010
> # else
> #  define RSEQ_SIG	0x00100350
> # endif
> #elif defined(__mips_micromips)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0xd4070000
> # else
> #  define RSEQ_SIG	0x0000d407
> # endif
> #else
> # define RSEQ_SIG	0x0350000d
> #endif
> 
> For plain old MIPS the .word directive will be fine endian-wise, but for
> microMIPS & nanoMIPS we need to take into account that the instruction
> stream is encoded as 16b halfwords & swap those accordingly for little
> endian.

Hi Paul,

Thanks for looking into it!

Does the following comment above the forest of #ifdef work for you ?

/*
 * RSEQ_SIG uses the break instruction. The instruction pattern is:
 *
 * On MIPS:
 *      0350000d        break     0x350
 *
 * On nanoMIPS32:
 *      00100350        break     0x350
 *
 * On microMIPS:
 *      0000d407        break     0x350
 *
 * For nanoMIPS32 and microMIPS, the instruction stream is encoded as 16-bit
 * halfwords, so the signature halfwords need to be swapped accordingly for
 * little-endian.
 */

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Paul Burton]

Hi Mathieu,

On Wed, Apr 24, 2019 at 07:12:03PM -0400, Mathieu Desnoyers wrote:
> Does the following comment above the forest of #ifdef work for you ?
> 
> /*
>  * RSEQ_SIG uses the break instruction. The instruction pattern is:
>  *
>  * On MIPS:
>  *      0350000d        break     0x350
>  *
>  * On nanoMIPS32:
>  *      00100350        break     0x350
>  *
>  * On microMIPS:
>  *      0000d407        break     0x350
>  *
>  * For nanoMIPS32 and microMIPS, the instruction stream is encoded as 16-bit
>  * halfwords, so the signature halfwords need to be swapped accordingly for
>  * little-endian.
>  */

I'd probably just say nanoMIPS rather than nanoMIPS32, because when we
get nanoMIPS64 in the future it'll be a superset of nanoMIPS32 & the
break encoding will be the same.

But otherwise it looks good to me :)

Thanks,
    Paul

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Mathieu Desnoyers]

----- On Apr 24, 2019, at 7:17 PM, Paul Burton paul.burton@mips.com wrote:

> Hi Mathieu,
> 
> On Wed, Apr 24, 2019 at 07:12:03PM -0400, Mathieu Desnoyers wrote:
>> Does the following comment above the forest of #ifdef work for you ?
>> 
>> /*
>>  * RSEQ_SIG uses the break instruction. The instruction pattern is:
>>  *
>>  * On MIPS:
>>  *      0350000d        break     0x350
>>  *
>>  * On nanoMIPS32:
>>  *      00100350        break     0x350
>>  *
>>  * On microMIPS:
>>  *      0000d407        break     0x350
>>  *
>>  * For nanoMIPS32 and microMIPS, the instruction stream is encoded as 16-bit
>>  * halfwords, so the signature halfwords need to be swapped accordingly for
>>  * little-endian.
>>  */
> 
> I'd probably just say nanoMIPS rather than nanoMIPS32, because when we
> get nanoMIPS64 in the future it'll be a superset of nanoMIPS32 & the
> break encoding will be the same.

Done.

> 
> But otherwise it looks good to me :)

Great! I've added your "Suggested-by" tag to the patch.

Thanks,

Mathieu

> 
> Thanks,
>     Paul

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Mathieu Desnoyers]

----- On Apr 24, 2019, at 6:06 PM, Paul Burton paul.burton@mips.com wrote:

> Hi Mathieu,
> 
> On Wed, Apr 24, 2019 at 11:25:02AM -0400, Mathieu Desnoyers wrote:
>> diff --git a/tools/testing/selftests/rseq/rseq-mips.h
>> b/tools/testing/selftests/rseq/rseq-mips.h
>> index fe3eabcdcbe5..eb53a6adfbbb 100644
>> --- a/tools/testing/selftests/rseq/rseq-mips.h
>> +++ b/tools/testing/selftests/rseq/rseq-mips.h
>> @@ -7,7 +7,11 @@
>>   * (C) Copyright 2016-2018 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>   */
>>  
>> -#define RSEQ_SIG	0x53053053
>> +/*
>> + * RSEQ_SIG uses the break instruction. The instruction pattern is
>> + *	0350000d        break    0x350
>> + */
>> +#define RSEQ_SIG	0x0350000d
> 
> My apologies for taking a while to get back to you on the various ISAs &
> endian issues here, but I think we'll want this to be something like:
> 
> #if defined(__nanomips__)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0x03500010
> # else
> #  define RSEQ_SIG	0x00100350
> # endif
> #elif defined(__mips_micromips)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0xd4070000
> # else
> #  define RSEQ_SIG	0x0000d407
> # endif
> #else
> # define RSEQ_SIG	0x0350000d
> #endif
> 
> For plain old MIPS the .word directive will be fine endian-wise, but for
> microMIPS & nanoMIPS we need to take into account that the instruction
> stream is encoded as 16b halfwords & swap those accordingly for little
> endian.

Considering that we have micromips and nanomips already, I guess something
along the lines of "picomips" is not that far away...

I've tried to figure out if we could find a way to have RSEQ_SIG left undefined
if it's not on the plain mips environment, but could not find anything that
would be #defined on plain mips, but #undefined on both micromips and nanomips.

What I'd like to do is e.g.:

#if defined(__nanomips__)
# ifdef __MIPSEL__
#  define RSEQ_SIG	0x03500010
# else
#  define RSEQ_SIG	0x00100350
# endif
#elif defined(__mips_micromips)
# ifdef __MIPSEL__
#  define RSEQ_SIG	0xd4070000
# else
#  define RSEQ_SIG	0x0000d407
# endif
#elif defined(__mips__)
# define RSEQ_SIG	0x0350000d
#else
/* Leave RSEQ_SIG as is. */
#endif

The idea here is to not allow code targeting future MIPS ISA to compile
with the wrong signature.

The delta between compiling without/with -mmicromips on a gcc-8 compiler
is only:

> #define __mips_micromips 1

Some interesting delta when compiling for plain little-endian mips with
gcc-8 compared to the nanomips compiler is:

< #define __mips__ 1
< #define _mips 1
< #define MIPSEL 1

> #define __nanomips__ 1

< #define __mips_isa_rev 2
> #define __mips_isa_rev 6

So let's say we have a picomips introduced in the future, can we rely
on it not defining __mips__ like the nanomips compiler does ? If so,
my "#elif defined(__mips__)" approach would indeed leave RSEQ_SIG undefined
as expected.

Thoughts ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [RFC PATCH for 5.2 10/10] rseq/selftests: mips: use break instruction for RSEQ_SIG

[Paul Burton]

Hi Mathieu,

On Thu, Apr 25, 2019 at 10:21:32AM -0400, Mathieu Desnoyers wrote:
> I've tried to figure out if we could find a way to have RSEQ_SIG left undefined
> if it's not on the plain mips environment, but could not find anything that
> would be #defined on plain mips, but #undefined on both micromips and nanomips.
> 
> What I'd like to do is e.g.:
> 
> #if defined(__nanomips__)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0x03500010
> # else
> #  define RSEQ_SIG	0x00100350
> # endif
> #elif defined(__mips_micromips)
> # ifdef __MIPSEL__
> #  define RSEQ_SIG	0xd4070000
> # else
> #  define RSEQ_SIG	0x0000d407
> # endif
> #elif defined(__mips__)
> # define RSEQ_SIG	0x0350000d
> #else
> /* Leave RSEQ_SIG as is. */
> #endif
> 
> The idea here is to not allow code targeting future MIPS ISA to compile
> with the wrong signature.
> 
> The delta between compiling without/with -mmicromips on a gcc-8 compiler
> is only:
> 
> > #define __mips_micromips 1
> 
> Some interesting delta when compiling for plain little-endian mips with
> gcc-8 compared to the nanomips compiler is:
> 
> < #define __mips__ 1
> < #define _mips 1
> < #define MIPSEL 1
> 
> > #define __nanomips__ 1
> 
> < #define __mips_isa_rev 2
> > #define __mips_isa_rev 6
> 
> So let's say we have a picomips introduced in the future, can we rely
> on it not defining __mips__ like the nanomips compiler does ? If so,
> my "#elif defined(__mips__)" approach would indeed leave RSEQ_SIG undefined
> as expected.
> 
> Thoughts ?

That seems like a reasonable approach to me. I don't think it'll be
guaranteed, but it'll give the best odds of the behavior you want.

If I recall correctly the reason for not defining __mips__ in the
nanoMIPS compiler was to force people to audit MIPS-specific code given
the scale of the changes in nanoMIPS - there are some incompatibilities
at the assembly level but more than that the ABI changes in multiple
ways from register assignment & calling convention to kernel-user struct
layouts & other things. If we were to build existing MIPS-specific code
as-is then some of this could lead to brokenness that the tools wouldn't
have a good way to detect & reject automatically, so making people audit
the code & add in the __nanomips__ check is a sort of safety measure.

So the likelihood of your code above picking up on any future ISA
changes will probably depend upon how incompatible they are, which seems
pretty sensible.

Thanks,
    Paul