[PATCH v2 00/12] ARM: ftrace fixes and cleanups

[PATCH v2 00/12] ARM: ftrace fixes and cleanups

[Ard Biesheuvel]

This series addresses a number of issues in the ARM support code for
ftrace, mostly related to Thumb2 but affecting other configurations as
well.

Changes since v1:
- add a couple of patches to enable ftrace in Thumb2 mode when building
  with Clang, which was the one remaining unsupported configuration
- fix up some minor code issues caught by the bots
- add some acks

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Cristian Marussi <cristian.marussi@arm.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>

Ard Biesheuvel (12):
  ARM: ftrace: ensure that ADR take Thumb bit into account
  ARM: ftrace: use ADD not POP to counter PUSH at entry
  ARM: ftrace: use trampolines to keep .init.text in branching range
  ARM: ftrace: avoid redundant loads or clobbering IP
  ARM: ftrace: avoid unnecessary literal loads
  ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST
  ARM: unwind: track location of LR value in stack frame
  ARM: ftrace: enable the graph tracer with the EABI unwinder
  ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds
  drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds
  ARM: cacheflush: avoid clobbering the frame pointer in Thumb2 mode
  Revert "ARM: 9144/1: forbid ftrace with clang and thumb2_kernel"

 arch/arm/Kconfig                         |   4 +-
 arch/arm/Kconfig.debug                   |   2 +-
 arch/arm/include/asm/cacheflush.h        |   7 +-
 arch/arm/include/asm/ftrace.h            |  20 +--
 arch/arm/include/asm/opcodes.h           |  14 +++
 arch/arm/include/asm/stacktrace.h        |   3 +
 arch/arm/kernel/Makefile                 |   6 +-
 arch/arm/kernel/entry-ftrace.S           | 128 +++++++++++---------
 arch/arm/kernel/ftrace.c                 |  51 ++++++--
 arch/arm/kernel/unwind.c                 |   7 +-
 arch/arm/mach-exynos/mcpm-exynos.c       |   7 +-
 arch/arm/probes/kprobes/actions-common.c |   6 +-
 arch/arm/probes/kprobes/actions-thumb.c  |  38 ++++--
 drivers/firmware/arm_scmi/Makefile       |   7 ++
 14 files changed, 193 insertions(+), 107 deletions(-)

-- 
2.30.2


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[PATCH v2 01/12] ARM: ftrace: ensure that ADR take Thumb bit into account

[Ard Biesheuvel]

Using ADR to take the address of 'ftrace_stub' via a local label
produces an address that has the Thumb bit cleared, which means the
subsequent comparison is guaranteed to fail. Instead, use the badr
macro, which forces the Thumb bit to be set.

Fixes: a3ba87a61499 ("ARM: 6316/1: ftrace: add Thumb-2 support")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm/kernel/entry-ftrace.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index a74289ebc803..f4886fb6e9ba 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -40,7 +40,7 @@
 	mcount_enter
 	ldr	r0, =ftrace_trace_function
 	ldr	r2, [r0]
-	adr	r0, .Lftrace_stub
+	badr	r0, .Lftrace_stub
 	cmp	r0, r2
 	bne	1f
 
-- 
2.30.2


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[PATCH v2 02/12] ARM: ftrace: use ADD not POP to counter PUSH at entry

[Ard Biesheuvel]

The compiler emitted hook used for ftrace consists of a PUSH {LR} to
preserve the link register, followed by a branch-and-link (BL) to
__gnu_mount_nc. Dynamic ftrace patches away the latter to turn the
combined sequence into a NOP, using a POP {LR} instruction.

This is not necessary, since the link register does not get clobbered in
this case, and simply adding #4 to the stack pointer is sufficient, and
avoids a memory access that may take a few cycles to resolve depending
on the micro-architecture.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm/kernel/entry-ftrace.S | 2 +-
 arch/arm/kernel/ftrace.c       | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index f4886fb6e9ba..dca12a09322a 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -27,7 +27,7 @@
  * allows it to be clobbered in subroutines and doesn't use it to hold
  * parameters.)
  *
- * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}"
+ * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4"
  * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c).
  */
 
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index a006585e1c09..db72d3a6522d 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -25,9 +25,9 @@
 #include <asm/patch.h>
 
 #ifdef CONFIG_THUMB2_KERNEL
-#define	NOP		0xf85deb04	/* pop.w {lr} */
+#define	NOP		0xf10d0d04	/* add.w sp, sp, #4 */
 #else
-#define	NOP		0xe8bd4000	/* pop {lr} */
+#define	NOP		0xe28dd004	/* add   sp, sp, #4 */
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-- 
2.30.2


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[PATCH v2 03/12] ARM: ftrace: use trampolines to keep .init.text in branching range

[Ard Biesheuvel]

Kernel images that are large in comparison to the range of a direct
branch may fail to work as expected with ftrace, as patching a direct
branch to one of the core ftrace routines may not be possible from the
.init.text section, if it is emitted too far away from the normal .text
section.

This is more likely to affect Thumb2 builds, given that its range is
only -/+ 16 MiB (as opposed to ARM which has -/+ 32 MiB), but may occur
in either ISA.

To work around this, add a couple of trampolines to .init.text and
swap these in when the ftrace patching code is operating on callers in
.init.text.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm/kernel/entry-ftrace.S | 16 ++++++++++++++
 arch/arm/kernel/ftrace.c       | 23 +++++++++++++++++---
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index dca12a09322a..237d435e29aa 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -270,3 +270,19 @@ ENTRY(ftrace_stub)
 .Lftrace_stub:
 	ret	lr
 ENDPROC(ftrace_stub)
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+	__INIT
+
+	.macro	init_tramp, dst:req
+ENTRY(\dst\()_from_init)
+	ldr	pc, =\dst
+ENDPROC(\dst\()_from_init)
+	.endm
+
+	init_tramp	ftrace_caller
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	init_tramp	ftrace_regs_caller
+#endif
+#endif
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index db72d3a6522d..cb9eb8a463c5 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -51,9 +51,20 @@ static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
 	return NOP;
 }
 
-static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
+void ftrace_caller_from_init(void);
+void ftrace_regs_caller_from_init(void);
+
+static unsigned long __ref adjust_address(struct dyn_ftrace *rec,
+					  unsigned long addr)
 {
-	return addr;
+	if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE) ||
+	    system_state >= SYSTEM_FREEING_INITMEM ||
+	    likely(!is_kernel_inittext(rec->ip)))
+		return addr;
+	if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) ||
+	    addr == (unsigned long)&ftrace_caller)
+		return (unsigned long)&ftrace_caller_from_init;
+	return (unsigned long)&ftrace_regs_caller_from_init;
 }
 
 int ftrace_arch_code_modify_prepare(void)
@@ -189,7 +200,13 @@ int ftrace_make_nop(struct module *mod,
 #endif
 
 	new = ftrace_nop_replace(rec);
-	ret = ftrace_modify_code(ip, old, new, true);
+	/*
+	 * Locations in .init.text may call __gnu_mcount_mc via a linker
+	 * emitted veneer if they are too far away from its implementation, and
+	 * so validation may fail spuriously in such cases. Let's work around
+	 * this by omitting those from validation.
+	 */
+	ret = ftrace_modify_code(ip, old, new, !is_kernel_inittext(ip));
 
 	return ret;
 }
-- 
2.30.2


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[PATCH v2 04/12] ARM: ftrace: avoid redundant loads or clobbering IP

[Ard Biesheuvel]

Tweak the ftrace return paths to avoid redundant loads of SP, as well as
unnecessary clobbering of IP.

This also fixes the inconsistency of using MOV to perform a function
return, which is sub-optimal on recent micro-architectures but more
importantly, does not perform an interworking return, unlike compiler
generated function returns in Thumb2 builds.

Let's fix this by popping PC from the stack like most ordinary code
does.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/kernel/entry-ftrace.S | 51 +++++++++-----------
 1 file changed, 22 insertions(+), 29 deletions(-)

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 237d435e29aa..67548c38a567 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -22,10 +22,7 @@
  * mcount can be thought of as a function called in the middle of a subroutine
  * call.  As such, it needs to be transparent for both the caller and the
  * callee: the original lr needs to be restored when leaving mcount, and no
- * registers should be clobbered.  (In the __gnu_mcount_nc implementation, we
- * clobber the ip register.  This is OK because the ARM calling convention
- * allows it to be clobbered in subroutines and doesn't use it to hold
- * parameters.)
+ * registers should be clobbered.
  *
  * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4"
  * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c).
@@ -70,26 +67,25 @@
 
 .macro __ftrace_regs_caller
 
-	sub	sp, sp, #8	@ space for PC and CPSR OLD_R0,
+	str	lr, [sp, #-8]!	@ store LR as PC and make space for CPSR/OLD_R0,
 				@ OLD_R0 will overwrite previous LR
 
-	add 	ip, sp, #12	@ move in IP the value of SP as it was
-				@ before the push {lr} of the mcount mechanism
+	ldr	lr, [sp, #8]    @ get previous LR
 
-	str     lr, [sp, #0]    @ store LR instead of PC
+	str	r0, [sp, #8]	@ write r0 as OLD_R0 over previous LR
 
-	ldr     lr, [sp, #8]    @ get previous LR
+	str	lr, [sp, #-4]!	@ store previous LR as LR
 
-	str	r0, [sp, #8]	@ write r0 as OLD_R0 over previous LR
+	add 	lr, sp, #16	@ move in LR the value of SP as it was
+				@ before the push {lr} of the mcount mechanism
 
-	stmdb   sp!, {ip, lr}
-	stmdb   sp!, {r0-r11, lr}
+	push	{r0-r11, ip, lr}
 
 	@ stack content at this point:
 	@ 0  4          48   52       56            60   64    68       72
-	@ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
+	@ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 |
 
-	mov r3, sp				@ struct pt_regs*
+	mov	r3, sp				@ struct pt_regs*
 
 	ldr r2, =function_trace_op
 	ldr r2, [r2]				@ pointer to the current
@@ -112,11 +108,9 @@ ftrace_graph_regs_call:
 #endif
 
 	@ pop saved regs
-	ldmia   sp!, {r0-r12}			@ restore r0 through r12
-	ldr	ip, [sp, #8]			@ restore PC
-	ldr	lr, [sp, #4]			@ restore LR
-	ldr	sp, [sp, #0]			@ restore SP
-	mov	pc, ip				@ return
+	pop	{r0-r11, ip, lr}		@ restore r0 through r12
+	ldr	lr, [sp], #4			@ restore LR
+	ldr	pc, [sp], #12
 .endm
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -132,11 +126,9 @@ ftrace_graph_regs_call:
 	bl	prepare_ftrace_return
 
 	@ pop registers saved in ftrace_regs_caller
-	ldmia   sp!, {r0-r12}			@ restore r0 through r12
-	ldr	ip, [sp, #8]			@ restore PC
-	ldr	lr, [sp, #4]			@ restore LR
-	ldr	sp, [sp, #0]			@ restore SP
-	mov	pc, ip				@ return
+	pop	{r0-r11, ip, lr}		@ restore r0 through r12
+	ldr	lr, [sp], #4			@ restore LR
+	ldr	pc, [sp], #12
 
 .endm
 #endif
@@ -202,16 +194,17 @@ ftrace_graph_call\suffix:
 .endm
 
 .macro mcount_exit
-	ldmia	sp!, {r0-r3, ip, lr}
-	ret	ip
+	ldmia	sp!, {r0-r3}
+	ldr	lr, [sp, #4]
+	ldr	pc, [sp], #8
 .endm
 
 ENTRY(__gnu_mcount_nc)
 UNWIND(.fnstart)
 #ifdef CONFIG_DYNAMIC_FTRACE
-	mov	ip, lr
-	ldmia	sp!, {lr}
-	ret	ip
+	push	{lr}
+	ldr	lr, [sp, #4]
+	ldr	pc, [sp], #8
 #else
 	__mcount
 #endif
-- 
2.30.2


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[PATCH v2 05/12] ARM: ftrace: avoid unnecessary literal loads

[Ard Biesheuvel]

Avoid explicit literal loads and instead, use accessor macros that
generate the optimal sequence depending on the architecture revision
being targeted.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm/kernel/entry-ftrace.S | 27 ++++++++------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 67548c38a567..99720064a4c5 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -35,23 +35,20 @@
 
 .macro __mcount suffix
 	mcount_enter
-	ldr	r0, =ftrace_trace_function
-	ldr	r2, [r0]
+	ldr_va	r2, ftrace_trace_function
 	badr	r0, .Lftrace_stub
 	cmp	r0, r2
 	bne	1f
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	ldr     r1, =ftrace_graph_return
-	ldr     r2, [r1]
-	cmp     r0, r2
-	bne     ftrace_graph_caller\suffix
-
-	ldr     r1, =ftrace_graph_entry
-	ldr     r2, [r1]
-	ldr     r0, =ftrace_graph_entry_stub
-	cmp     r0, r2
-	bne     ftrace_graph_caller\suffix
+	ldr_va	r2, ftrace_graph_return
+	cmp	r0, r2
+	bne	ftrace_graph_caller\suffix
+
+	ldr_va	r2, ftrace_graph_entry
+	mov_l	r0, ftrace_graph_entry_stub
+	cmp	r0, r2
+	bne	ftrace_graph_caller\suffix
 #endif
 
 	mcount_exit
@@ -87,8 +84,7 @@
 
 	mov	r3, sp				@ struct pt_regs*
 
-	ldr r2, =function_trace_op
-	ldr r2, [r2]				@ pointer to the current
+	ldr_va	r2, function_trace_op		@ pointer to the current
 						@ function tracing op
 
 	ldr	r1, [sp, #S_LR]			@ lr of instrumented func
@@ -141,8 +137,7 @@ ftrace_graph_regs_call:
 	mcount_adjust_addr	r0, lr		@ instrumented function
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
-	ldr r2, =function_trace_op
-	ldr r2, [r2]				@ pointer to the current
+	ldr_va	r2, function_trace_op		@ pointer to the current
 						@ function tracing op
 	mov r3, #0				@ regs is NULL
 #endif
-- 
2.30.2


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[PATCH v2 06/12] ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST

[Ard Biesheuvel]

Fix the frame pointer handling in the function graph tracer entry and
exit code so we can enable HAVE_FUNCTION_GRAPH_FP_TEST. Instead of using
FP directly (which will have different values between the entry and exit
pieces of the function graph tracer), use the value of SP at entry and
exit, as we can derive the former value from the frame pointer.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/ftrace.h  | 2 ++
 arch/arm/kernel/entry-ftrace.S | 2 +-
 arch/arm/kernel/ftrace.c       | 5 +++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index a4dbac07e4ef..b4f5fab6b04e 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -2,6 +2,8 @@
 #ifndef _ASM_ARM_FTRACE
 #define _ASM_ARM_FTRACE
 
+#define HAVE_FUNCTION_GRAPH_FP_TEST
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #endif
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 99720064a4c5..bbfa0954c385 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -247,7 +247,7 @@ ENDPROC(ftrace_graph_regs_caller)
 	.globl return_to_handler
 return_to_handler:
 	stmdb	sp!, {r0-r3}
-	mov	r0, fp			@ frame pointer
+	add	r0, sp, #16		@ sp at exit of instrumented routine
 	bl	ftrace_return_to_handler
 	mov	lr, r0			@ r0 has real ret addr
 	ldmia	sp!, {r0-r3}
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index cb9eb8a463c5..1885c3fec15a 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -222,6 +222,11 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		return;
 
+	if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) {
+		/* FP points one word below parent's top of stack */
+		frame_pointer += 4;
+	}
+
 	old = *parent;
 	*parent = return_hooker;
 
-- 
2.30.2


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[PATCH v2 07/12] ARM: unwind: track location of LR value in stack frame

[Ard Biesheuvel]

The ftrace graph tracer needs to override the return address of an
instrumented function, in order to install a hook that gets invoked when
the function returns again.

Currently, we only support this when building for ARM using GCC with
frame pointers, as in this case, it is guaranteed that the function will
reload LR from [FP, #-4] in all cases, and we can simply pass that
address to the ftrace code.

In order to support this for configurations that rely on the EABI
unwinder, such as Thumb2 builds, make the unwinder keep track of the
address from which LR was unwound, permitting ftrace to make use of this
in a subsequent patch.

Drop the call to is_kernel_text_address(), which is problematic in terms
of ftrace recursion, given that it may be instrumented itself. The call
is redundant anyway, as no unwind directives will be found unless the PC
points to memory that is known to contain executable code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/stacktrace.h | 3 +++
 arch/arm/kernel/Makefile          | 1 +
 arch/arm/kernel/unwind.c          | 7 ++++---
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/stacktrace.h b/arch/arm/include/asm/stacktrace.h
index d87d60532b86..e56503fd9447 100644
--- a/arch/arm/include/asm/stacktrace.h
+++ b/arch/arm/include/asm/stacktrace.h
@@ -14,6 +14,9 @@ struct stackframe {
 	unsigned long sp;
 	unsigned long lr;
 	unsigned long pc;
+
+	/* address of the LR value on the stack */
+	unsigned long *lr_addr;
 #ifdef CONFIG_KRETPROBES
 	struct llist_node *kr_cur;
 	struct task_struct *tsk;
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index ae295a3bcfef..56511856ff9d 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -10,6 +10,7 @@ ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_insn.o = -pg
 CFLAGS_REMOVE_patch.o = -pg
+CFLAGS_REMOVE_unwind.o = -pg
 endif
 
 CFLAGS_REMOVE_return_address.o = -pg
diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index c5ea328c428d..b4e468a7674b 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -55,6 +55,7 @@ struct unwind_ctrl_block {
 	const unsigned long *insn;	/* pointer to the current instructions word */
 	unsigned long sp_low;		/* lowest value of sp allowed */
 	unsigned long sp_high;		/* highest value of sp allowed */
+	unsigned long *lr_addr;		/* address of LR value on the stack */
 	/*
 	 * 1 : check for stack overflow for each register pop.
 	 * 0 : save overhead if there is plenty of stack remaining.
@@ -239,6 +240,8 @@ static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
 	 * from being tracked by KASAN.
 	 */
 	ctrl->vrs[reg] = READ_ONCE_NOCHECK(*(*vsp));
+	if (reg == 14)
+		ctrl->lr_addr = *vsp;
 	(*vsp)++;
 	return URC_OK;
 }
@@ -395,9 +398,6 @@ int unwind_frame(struct stackframe *frame)
 	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
 		 frame->pc, frame->lr, frame->sp);
 
-	if (!kernel_text_address(frame->pc))
-		return -URC_FAILURE;
-
 	idx = unwind_find_idx(frame->pc);
 	if (!idx) {
 		pr_warn("unwind: Index not found %08lx\n", frame->pc);
@@ -476,6 +476,7 @@ int unwind_frame(struct stackframe *frame)
 	frame->lr = ctrl.vrs[LR];
 	frame->pc = ctrl.vrs[PC];
 	frame->sp_low = ctrl.sp_low;
+	frame->lr_addr = ctrl.lr_addr;
 
 	return URC_OK;
 }
-- 
2.30.2


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[PATCH v2 08/12] ARM: ftrace: enable the graph tracer with the EABI unwinder

[Ard Biesheuvel]

Enable the function graph tracer in combination with the EABI unwinder,
so that Thumb2 builds or Clang ARM builds can make use of it.

This involves using the unwinder to locate the return address of an
instrumented function on the stack, so that it can be overridden and
made to refer to the ftrace handling routines that need to be called at
function return.

Given that for these builds, it is not guaranteed that the value of the
link register is stored on the stack, fall back to the stack slot that
will be used by the ftrace exit code to restore LR in the instrumented
function's execution context.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/Kconfig               |  2 +-
 arch/arm/Kconfig.debug         |  2 +-
 arch/arm/include/asm/ftrace.h  | 18 -------------
 arch/arm/kernel/Makefile       |  5 +---
 arch/arm/kernel/entry-ftrace.S | 28 ++++++++++++++------
 arch/arm/kernel/ftrace.c       | 19 +++++++++++--
 6 files changed, 40 insertions(+), 34 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8eff55222874..3c6216f194f2 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -92,7 +92,7 @@ config ARM
 	select HAVE_EXIT_THREAD
 	select HAVE_FAST_GUP if ARM_LPAE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
-	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
+	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 07055a503022..cc7523f44be4 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER
 
 config UNWINDER_ARM
 	bool "ARM EABI stack unwinder"
-	depends on AEABI && !FUNCTION_GRAPH_TRACER
+	depends on AEABI
 	# https://github.com/ClangBuiltLinux/linux/issues/732
 	depends on !LD_IS_LLD || LLD_VERSION >= 110000
 	select ARM_UNWIND
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index b4f5fab6b04e..5358aad67831 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -35,26 +35,8 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 
 #ifndef __ASSEMBLY__
 
-#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
-/*
- * return_address uses walk_stackframe to do it's work.  If both
- * CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind
- * information.  For this to work in the function tracer many functions would
- * have to be marked with __notrace.  So for now just depend on
- * !CONFIG_ARM_UNWIND.
- */
-
 void *return_address(unsigned int);
 
-#else
-
-static inline void *return_address(unsigned int level)
-{
-	return NULL;
-}
-
-#endif
-
 #define ftrace_return_address(n) return_address(n)
 
 #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 56511856ff9d..5cebb8d5a1d6 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -25,10 +25,7 @@ obj-y		:= elf.o entry-common.o irq.o opcodes.o \
 KASAN_SANITIZE_stacktrace.o := n
 KASAN_SANITIZE_traps.o := n
 
-ifneq ($(CONFIG_ARM_UNWIND),y)
-obj-$(CONFIG_FRAME_POINTER)	+= return_address.o
-endif
-
+obj-y				+= return_address.o
 obj-$(CONFIG_ATAGS)		+= atags_parse.o
 obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o
 obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index bbfa0954c385..3e7bcaca5e07 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -100,7 +100,8 @@ ftrace_regs_call:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	.globl ftrace_graph_regs_call
 ftrace_graph_regs_call:
-	mov	r0, r0
+ARM(	mov	r0, r0	)
+THUMB(	nop.w		)
 #endif
 
 	@ pop saved regs
@@ -112,13 +113,18 @@ ftrace_graph_regs_call:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 .macro __ftrace_graph_regs_caller
 
-	sub     r0, fp, #4              @ lr of instrumented routine (parent)
+#ifdef CONFIG_UNWINDER_FRAME_POINTER
+	sub	r0, fp, #4		@ lr of instrumented routine (parent)
+#else
+	add	r0, sp, #S_LR
+#endif
 
 	@ called from __ftrace_regs_caller
-	ldr     r1, [sp, #S_PC]		@ instrumented routine (func)
+	ldr	r1, [sp, #S_PC]		@ instrumented routine (func)
 	mcount_adjust_addr	r1, r1
 
-	mov	r2, fp			@ frame pointer
+	mov	r2, fpreg		@ frame pointer
+	add	r3, sp, #PT_REGS_SIZE
 	bl	prepare_ftrace_return
 
 	@ pop registers saved in ftrace_regs_caller
@@ -149,14 +155,19 @@ ftrace_call\suffix:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	.globl ftrace_graph_call\suffix
 ftrace_graph_call\suffix:
-	mov	r0, r0
+ARM(	mov	r0, r0	)
+THUMB(	nop.w		)
 #endif
 
 	mcount_exit
 .endm
 
 .macro __ftrace_graph_caller
+#ifdef CONFIG_UNWINDER_FRAME_POINTER
 	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)
+#else
+	add	r0, sp, #20
+#endif
 #ifdef CONFIG_DYNAMIC_FTRACE
 	@ called from __ftrace_caller, saved in mcount_enter
 	ldr	r1, [sp, #16]		@ instrumented routine (func)
@@ -165,7 +176,8 @@ ftrace_graph_call\suffix:
 	@ called from __mcount, untouched in lr
 	mcount_adjust_addr	r1, lr	@ instrumented routine (func)
 #endif
-	mov	r2, fp			@ frame pointer
+	mov	r2, fpreg		@ frame pointer
+	add	r3, sp, #24
 	bl	prepare_ftrace_return
 	mcount_exit
 .endm
@@ -244,14 +256,14 @@ ENDPROC(ftrace_graph_regs_caller)
 .purgem mcount_exit
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	.globl return_to_handler
-return_to_handler:
+ENTRY(return_to_handler)
 	stmdb	sp!, {r0-r3}
 	add	r0, sp, #16		@ sp at exit of instrumented routine
 	bl	ftrace_return_to_handler
 	mov	lr, r0			@ r0 has real ret addr
 	ldmia	sp!, {r0-r3}
 	ret	lr
+ENDPROC(return_to_handler)
 #endif
 
 ENTRY(ftrace_stub)
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 1885c3fec15a..cd0b33eef6b8 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -22,6 +22,7 @@
 #include <asm/ftrace.h>
 #include <asm/insn.h>
 #include <asm/set_memory.h>
+#include <asm/stacktrace.h>
 #include <asm/patch.h>
 
 #ifdef CONFIG_THUMB2_KERNEL
@@ -213,8 +214,10 @@ int ftrace_make_nop(struct module *mod,
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+asmlinkage
 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
-			   unsigned long frame_pointer)
+			   unsigned long frame_pointer,
+			   unsigned long stack_pointer)
 {
 	unsigned long return_hooker = (unsigned long) &return_to_handler;
 	unsigned long old;
@@ -225,6 +228,18 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 	if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) {
 		/* FP points one word below parent's top of stack */
 		frame_pointer += 4;
+	} else {
+		struct stackframe frame = {
+			.fp = frame_pointer,
+			.sp = stack_pointer,
+			.lr = self_addr,
+			.pc = self_addr,
+		};
+		if (unwind_frame(&frame) < 0)
+			return;
+		if (frame.lr != self_addr)
+			parent = frame.lr_addr;
+		frame_pointer = frame.sp;
 	}
 
 	old = *parent;
@@ -247,7 +262,7 @@ static int __ftrace_modify_caller(unsigned long *callsite,
 	unsigned long caller_fn = (unsigned long) func;
 	unsigned long pc = (unsigned long) callsite;
 	unsigned long branch = arm_gen_branch(pc, caller_fn);
-	unsigned long nop = 0xe1a00000;	/* mov r0, r0 */
+	unsigned long nop = arm_gen_nop();
 	unsigned long old = enable ? nop : branch;
 	unsigned long new = enable ? branch : nop;
 
-- 
2.30.2


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[PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Ard Biesheuvel]

Thumb2 code uses R7 as the frame pointer rather than R11, because the
opcodes to access it are generally shorter.

This means that there are cases where we cannot simply add it to the
clobber list of an asm() block, but need to preserve/restore it
explicitly, or the compiler may complain in some cases (e.g., Clang
builds with ftrace enabled).

Since R11 is not special in that case, clobber it instead, and use it to
preserve/restore the value of R7.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/opcodes.h           | 14 ++++++++
 arch/arm/probes/kprobes/actions-common.c |  6 ++--
 arch/arm/probes/kprobes/actions-thumb.c  | 38 ++++++++++++++++----
 3 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
index 38e3eabff5c3..9a6362408ea0 100644
--- a/arch/arm/include/asm/opcodes.h
+++ b/arch/arm/include/asm/opcodes.h
@@ -230,4 +230,18 @@ extern __u32 __opcode_to_mem_thumb32(__u32);
 	".short " __stringify(first) ", " __stringify(second) "\n\t"
 #endif
 
+/*
+ * Which register to preserve and which register can be clobbered in inline asm
+ * that needs to be compatible with code that emits frame pointers.
+ */
+#ifdef CONFIG_THUMB2_KERNEL
+#define FPREG_PRESERVE	"r7"
+#define FPREG_CLOBBER	"r11"
+#define FPREG_PRESERVE_R7
+#else
+#define FPREG_PRESERVE	"fp"
+#define FPREG_CLOBBER	"r7"
+#define FPREG_PRESERVE_R11
+#endif
+
 #endif /* __ASM_ARM_OPCODES_H */
diff --git a/arch/arm/probes/kprobes/actions-common.c b/arch/arm/probes/kprobes/actions-common.c
index 836aebe596cd..f0efe16e2fdb 100644
--- a/arch/arm/probes/kprobes/actions-common.c
+++ b/arch/arm/probes/kprobes/actions-common.c
@@ -84,7 +84,7 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
 	register void *rfn asm("lr") = asi->insn_fn;
 
 	__asm__ __volatile__ (
-		"stmdb	sp!, {%[regs], r11}	\n\t"
+		"stmdb	sp!, {%[regs], " FPREG_PRESERVE "}\n\t"
 		"ldmia	%[regs], {r0-r12}	\n\t"
 #if __LINUX_ARM_ARCH__ >= 6
 		"blx	%[fn]			\n\t"
@@ -96,10 +96,10 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
 #endif
 		"ldr	lr, [sp], #4		\n\t" /* lr = regs */
 		"stmia	lr, {r0-r12}		\n\t"
-		"ldr	r11, [sp], #4		\n\t"
+		"ldr	" FPREG_PRESERVE ", [sp], #4\n\t"
 		: [regs] "=r" (rregs), [fn] "=r" (rfn)
 		: "0" (rregs), "1" (rfn)
-		: "r0", "r2", "r3", "r4", "r5", "r6", "r7",
+		: "r0", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
 		  "r8", "r9", "r10", "r12", "memory", "cc"
 		);
 }
diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
index 7884fcb81c26..873757326533 100644
--- a/arch/arm/probes/kprobes/actions-thumb.c
+++ b/arch/arm/probes/kprobes/actions-thumb.c
@@ -447,14 +447,20 @@ t16_emulate_loregs(probes_opcode_t insn,
 
 	__asm__ __volatile__ (
 		"msr	cpsr_fs, %[oldcpsr]	\n\t"
+#ifdef FPREG_PRESERVE_R7
+		"mov	fp, r7			\n\t"
+#endif
 		"ldmia	%[regs], {r0-r7}	\n\t"
 		"blx	%[fn]			\n\t"
 		"stmia	%[regs], {r0-r7}	\n\t"
+#ifdef FPREG_PRESERVE_R7
+		"mov	r7, fp			\n\t"
+#endif
 		"mrs	%[newcpsr], cpsr	\n\t"
 		: [newcpsr] "=r" (newcpsr)
 		: [oldcpsr] "r" (oldcpsr), [regs] "r" (regs),
 		  [fn] "r" (asi->insn_fn)
-		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
+		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
 		  "lr", "memory", "cc"
 		);
 
@@ -524,15 +530,21 @@ t16_emulate_push(probes_opcode_t insn,
 		struct arch_probes_insn *asi, struct pt_regs *regs)
 {
 	__asm__ __volatile__ (
+#ifdef FPREG_PRESERVE_R7
+		"mov	fp, r7			\n\t"
+#endif
 		"ldr	r9, [%[regs], #13*4]	\n\t"
 		"ldr	r8, [%[regs], #14*4]	\n\t"
 		"ldmia	%[regs], {r0-r7}	\n\t"
 		"blx	%[fn]			\n\t"
 		"str	r9, [%[regs], #13*4]	\n\t"
+#ifdef FPREG_PRESERVE_R7
+		"mov	r7, fp			\n\t"
+#endif
 		:
 		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
-		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
-		  "lr", "memory", "cc"
+		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r8", "r9",
+		  FPREG_CLOBBER, "lr", "memory", "cc"
 		);
 }
 
@@ -558,15 +570,21 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
 		struct arch_probes_insn *asi, struct pt_regs *regs)
 {
 	__asm__ __volatile__ (
+#ifdef FPREG_PRESERVE_R7
+		"mov	fp, r7			\n\t"
+#endif
 		"ldr	r9, [%[regs], #13*4]	\n\t"
 		"ldmia	%[regs], {r0-r7}	\n\t"
 		"blx	%[fn]			\n\t"
 		"stmia	%[regs], {r0-r7}	\n\t"
 		"str	r9, [%[regs], #13*4]	\n\t"
+#ifdef FPREG_PRESERVE_R7
+		"mov	r7, fp			\n\t"
+#endif
 		:
 		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
-		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
-		  "lr", "memory", "cc"
+		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
+		  FPREG_CLOBBER, "lr", "memory", "cc"
 		);
 }
 
@@ -577,15 +595,21 @@ t16_emulate_pop_pc(probes_opcode_t insn,
 	register unsigned long pc asm("r8");
 
 	__asm__ __volatile__ (
+#ifdef FPREG_PRESERVE_R7
+		"mov	fp, r7			\n\t"
+#endif
 		"ldr	r9, [%[regs], #13*4]	\n\t"
 		"ldmia	%[regs], {r0-r7}	\n\t"
 		"blx	%[fn]			\n\t"
 		"stmia	%[regs], {r0-r7}	\n\t"
 		"str	r9, [%[regs], #13*4]	\n\t"
+#ifdef FPREG_PRESERVE_R7
+		"mov	r7, fp			\n\t"
+#endif
 		: "=r" (pc)
 		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
-		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
-		  "lr", "memory", "cc"
+		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
+		  FPREG_CLOBBER, "lr", "memory", "cc"
 		);
 
 	bx_write_pc(pc, regs);
-- 
2.30.2


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[PATCH v2 10/12] drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds

[Ard Biesheuvel]

The SMC calling convention designates R0-R7 as input registers in
AArch32 mode, and this conflicts with the compiler's use of R7 as a
frame pointer when building in Thumb2 mode. Generally, we don't enable
the frame pointer, and GCC happily enables the -pg profiling hooks
without them. However, Clang refuses, and errors out with the message
below:

drivers/firmware/arm_scmi/smc.c:152:2: error: write to reserved register 'R7'
        arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
        ^
include/linux/arm-smccc.h:550:4: note: expanded from macro 'arm_smccc_1_1_invoke'
                        arm_smccc_1_1_smc(__VA_ARGS__);                 \
                        ^
Let's just disable ftrace for the compilation unit when building this
configuration.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/arm_scmi/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
index 1dcf123d64ab..52b9078bfe96 100644
--- a/drivers/firmware/arm_scmi/Makefile
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -11,3 +11,10 @@ scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
 		    $(scmi-transport-y)
 obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-module.o
 obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o
+
+ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy)
+# The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame
+# pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling
+# hooks are inserted via the -pg switch.
+CFLAGS_REMOVE_smc.o += $(CC_FLAGS_FTRACE)
+endif
-- 
2.30.2


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[PATCH v2 11/12] ARM: cacheflush: avoid clobbering the frame pointer in Thumb2 mode

[Ard Biesheuvel]

Thumb2 uses R7 rather than R11 as the frame pointer, and even if we
rarely use a frame pointer to begin with when building in Thumb2 mode,
there are cases where it is required by the compiler (Clang when
inserting profiling hooks via -pg)

So let's preserve whichever register is considered the frame pointer
depending on whether we are building for ARM or Thumb2, rather than
preserving/restoring R11 explicitly.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/cacheflush.h  | 7 ++++---
 arch/arm/mach-exynos/mcpm-exynos.c | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index e68fb879e4f9..5c4c49086ac6 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -12,6 +12,7 @@
 #include <asm/glue-cache.h>
 #include <asm/shmparam.h>
 #include <asm/cachetype.h>
+#include <asm/opcodes.h>
 #include <asm/outercache.h>
 
 #define CACHE_COLOUR(vaddr)	((vaddr & (SHMLBA - 1)) >> PAGE_SHIFT)
@@ -454,7 +455,7 @@ static inline void __sync_cache_range_r(volatile void *p, size_t size)
 #define v7_exit_coherency_flush(level) \
 	asm volatile( \
 	".arch	armv7-a \n\t" \
-	"stmfd	sp!, {fp, ip} \n\t" \
+	"stmfd	sp!, {" FPREG_PRESERVE ", ip} \n\t" \
 	"mrc	p15, 0, r0, c1, c0, 0	@ get SCTLR \n\t" \
 	"bic	r0, r0, #"__stringify(CR_C)" \n\t" \
 	"mcr	p15, 0, r0, c1, c0, 0	@ set SCTLR \n\t" \
@@ -465,8 +466,8 @@ static inline void __sync_cache_range_r(volatile void *p, size_t size)
 	"mcr	p15, 0, r0, c1, c0, 1	@ set ACTLR \n\t" \
 	"isb	\n\t" \
 	"dsb	\n\t" \
-	"ldmfd	sp!, {fp, ip}" \
-	: : : "r0","r1","r2","r3","r4","r5","r6","r7", \
+	"ldmfd	sp!, {" FPREG_PRESERVE ", ip}" \
+	: : : "r0","r1","r2","r3","r4","r5","r6", FPREG_CLOBBER, \
 	      "r9","r10","lr","memory" )
 
 void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
index cd861c57d5ad..0cebc008d877 100644
--- a/arch/arm/mach-exynos/mcpm-exynos.c
+++ b/arch/arm/mach-exynos/mcpm-exynos.c
@@ -14,6 +14,7 @@
 #include <asm/cputype.h>
 #include <asm/cp15.h>
 #include <asm/mcpm.h>
+#include <asm/opcodes.h>
 #include <asm/smp_plat.h>
 
 #include "common.h"
@@ -35,7 +36,7 @@ static bool secure_firmware __ro_after_init;
  */
 #define exynos_v7_exit_coherency_flush(level) \
 	asm volatile( \
-	"stmfd	sp!, {fp, ip}\n\t"\
+	"stmfd	sp!, {" FPREG_PRESERVE ", ip} \n\t" \
 	"mrc	p15, 0, r0, c1, c0, 0	@ get SCTLR\n\t" \
 	"bic	r0, r0, #"__stringify(CR_C)"\n\t" \
 	"mcr	p15, 0, r0, c1, c0, 0	@ set SCTLR\n\t" \
@@ -50,10 +51,10 @@ static bool secure_firmware __ro_after_init;
 	"mcr	p15, 0, r0, c1, c0, 1	@ set ACTLR\n\t" \
 	"isb\n\t" \
 	"dsb\n\t" \
-	"ldmfd	sp!, {fp, ip}" \
+	"ldmfd	sp!, {" FPREG_PRESERVE ", ip}" \
 	: \
 	: "Ir" (pmu_base_addr + S5P_INFORM0) \
-	: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", \
+	: "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER, \
 	  "r9", "r10", "lr", "memory")
 
 static int exynos_cpu_powerup(unsigned int cpu, unsigned int cluster)
-- 
2.30.2


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[PATCH v2 12/12] Revert "ARM: 9144/1: forbid ftrace with clang and thumb2_kernel"

[Ard Biesheuvel]

This reverts commit ecb108e3e3f7c692082b7c6fce41779c3835854a.

Clang + Thumb2 with ftrace is now supported.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 3c6216f194f2..4ad7080bc17c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -93,7 +93,7 @@ config ARM
 	select HAVE_FAST_GUP if ARM_LPAE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
-	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
+	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
-- 
2.30.2


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Re: [PATCH v2 00/12] ARM: ftrace fixes and cleanups

[Steven Rostedt]

On Mon, 31 Jan 2022 18:03:35 +0100
Ard Biesheuvel <ardb@kernel.org> wrote:

> This series addresses a number of issues in the ARM support code for
> ftrace, mostly related to Thumb2 but affecting other configurations as
> well.
> 
> Changes since v1:
> - add a couple of patches to enable ftrace in Thumb2 mode when building
>   with Clang, which was the one remaining unsupported configuration
> - fix up some minor code issues caught by the bots
> - add some acks
> 
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Cristian Marussi <cristian.marussi@arm.com>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> 
> Ard Biesheuvel (12):
>   ARM: ftrace: ensure that ADR take Thumb bit into account
>   ARM: ftrace: use ADD not POP to counter PUSH at entry
>   ARM: ftrace: use trampolines to keep .init.text in branching range
>   ARM: ftrace: avoid redundant loads or clobbering IP
>   ARM: ftrace: avoid unnecessary literal loads
>   ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST
>   ARM: unwind: track location of LR value in stack frame
>   ARM: ftrace: enable the graph tracer with the EABI unwinder
>   ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds
>   drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds
>   ARM: cacheflush: avoid clobbering the frame pointer in Thumb2 mode
>   Revert "ARM: 9144/1: forbid ftrace with clang and thumb2_kernel"
> 

I'm not strong on ARM assembly, but to the best of my ability and reading
the change logs, the "ftrace" portions look good.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Nick Desaulniers]

On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> Thumb2 code uses R7 as the frame pointer rather than R11, because the
> opcodes to access it are generally shorter.
>
> This means that there are cases where we cannot simply add it to the
> clobber list of an asm() block, but need to preserve/restore it
> explicitly, or the compiler may complain in some cases (e.g., Clang
> builds with ftrace enabled).
>
> Since R11 is not special in that case, clobber it instead, and use it to
> preserve/restore the value of R7.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/arm/include/asm/opcodes.h           | 14 ++++++++
>  arch/arm/probes/kprobes/actions-common.c |  6 ++--
>  arch/arm/probes/kprobes/actions-thumb.c  | 38 ++++++++++++++++----
>  3 files changed, 48 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
> index 38e3eabff5c3..9a6362408ea0 100644
> --- a/arch/arm/include/asm/opcodes.h
> +++ b/arch/arm/include/asm/opcodes.h
> @@ -230,4 +230,18 @@ extern __u32 __opcode_to_mem_thumb32(__u32);
>         ".short " __stringify(first) ", " __stringify(second) "\n\t"
>  #endif
>
> +/*
> + * Which register to preserve and which register can be clobbered in inline asm
> + * that needs to be compatible with code that emits frame pointers.
> + */
> +#ifdef CONFIG_THUMB2_KERNEL
> +#define FPREG_PRESERVE "r7"
> +#define FPREG_CLOBBER  "r11"
> +#define FPREG_PRESERVE_R7
> +#else
> +#define FPREG_PRESERVE "fp"
> +#define FPREG_CLOBBER  "r7"
> +#define FPREG_PRESERVE_R11

I think you might be able to get away without FPREG_PRESERVE_R11 and
even without FPREG_PRESERVE_R7. FPREG_PRESERVE_R11 is currently unused
and FPREG_PRESERVE_R7 is synonymous with CONFIG_THUMB2_KERNEL at the
moment (It doesn't look like patches 11 or 12 change that either).
Looking at arch/arm/probes/kprobes/Makefile,
arch/arm/probes/kprobes/actions-thumb.c is only built when
CONFIG_THUMB2_KERNEL is enabled, so I don't think the #ifdefs are
required; those `mov`s could be unguarded by the preprocessor?

> +#endif
> +
>  #endif /* __ASM_ARM_OPCODES_H */
> diff --git a/arch/arm/probes/kprobes/actions-common.c b/arch/arm/probes/kprobes/actions-common.c
> index 836aebe596cd..f0efe16e2fdb 100644
> --- a/arch/arm/probes/kprobes/actions-common.c
> +++ b/arch/arm/probes/kprobes/actions-common.c
> @@ -84,7 +84,7 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
>         register void *rfn asm("lr") = asi->insn_fn;
>
>         __asm__ __volatile__ (
> -               "stmdb  sp!, {%[regs], r11}     \n\t"
> +               "stmdb  sp!, {%[regs], " FPREG_PRESERVE "}\n\t"
>                 "ldmia  %[regs], {r0-r12}       \n\t"
>  #if __LINUX_ARM_ARCH__ >= 6
>                 "blx    %[fn]                   \n\t"
> @@ -96,10 +96,10 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
>  #endif
>                 "ldr    lr, [sp], #4            \n\t" /* lr = regs */
>                 "stmia  lr, {r0-r12}            \n\t"
> -               "ldr    r11, [sp], #4           \n\t"
> +               "ldr    " FPREG_PRESERVE ", [sp], #4\n\t"
>                 : [regs] "=r" (rregs), [fn] "=r" (rfn)
>                 : "0" (rregs), "1" (rfn)
> -               : "r0", "r2", "r3", "r4", "r5", "r6", "r7",
> +               : "r0", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
>                   "r8", "r9", "r10", "r12", "memory", "cc"
>                 );
>  }
> diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
> index 7884fcb81c26..873757326533 100644
> --- a/arch/arm/probes/kprobes/actions-thumb.c
> +++ b/arch/arm/probes/kprobes/actions-thumb.c
> @@ -447,14 +447,20 @@ t16_emulate_loregs(probes_opcode_t insn,
>
>         __asm__ __volatile__ (
>                 "msr    cpsr_fs, %[oldcpsr]     \n\t"
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    fp, r7                  \n\t"
> +#endif
>                 "ldmia  %[regs], {r0-r7}        \n\t"
>                 "blx    %[fn]                   \n\t"
>                 "stmia  %[regs], {r0-r7}        \n\t"
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    r7, fp                  \n\t"
> +#endif
>                 "mrs    %[newcpsr], cpsr        \n\t"
>                 : [newcpsr] "=r" (newcpsr)
>                 : [oldcpsr] "r" (oldcpsr), [regs] "r" (regs),
>                   [fn] "r" (asi->insn_fn)
> -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
> +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
>                   "lr", "memory", "cc"
>                 );
>
> @@ -524,15 +530,21 @@ t16_emulate_push(probes_opcode_t insn,
>                 struct arch_probes_insn *asi, struct pt_regs *regs)
>  {
>         __asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    fp, r7                  \n\t"
> +#endif
>                 "ldr    r9, [%[regs], #13*4]    \n\t"
>                 "ldr    r8, [%[regs], #14*4]    \n\t"
>                 "ldmia  %[regs], {r0-r7}        \n\t"
>                 "blx    %[fn]                   \n\t"
>                 "str    r9, [%[regs], #13*4]    \n\t"
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    r7, fp                  \n\t"
> +#endif
>                 :
>                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
> -                 "lr", "memory", "cc"
> +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r8", "r9",
> +                 FPREG_CLOBBER, "lr", "memory", "cc"
>                 );
>  }
>
> @@ -558,15 +570,21 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
>                 struct arch_probes_insn *asi, struct pt_regs *regs)
>  {
>         __asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    fp, r7                  \n\t"
> +#endif
>                 "ldr    r9, [%[regs], #13*4]    \n\t"
>                 "ldmia  %[regs], {r0-r7}        \n\t"
>                 "blx    %[fn]                   \n\t"
>                 "stmia  %[regs], {r0-r7}        \n\t"
>                 "str    r9, [%[regs], #13*4]    \n\t"
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    r7, fp                  \n\t"
> +#endif
>                 :
>                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> -                 "lr", "memory", "cc"
> +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> +                 FPREG_CLOBBER, "lr", "memory", "cc"
>                 );
>  }
>
> @@ -577,15 +595,21 @@ t16_emulate_pop_pc(probes_opcode_t insn,
>         register unsigned long pc asm("r8");
>
>         __asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    fp, r7                  \n\t"
> +#endif
>                 "ldr    r9, [%[regs], #13*4]    \n\t"
>                 "ldmia  %[regs], {r0-r7}        \n\t"
>                 "blx    %[fn]                   \n\t"
>                 "stmia  %[regs], {r0-r7}        \n\t"
>                 "str    r9, [%[regs], #13*4]    \n\t"
> +#ifdef FPREG_PRESERVE_R7
> +               "mov    r7, fp                  \n\t"
> +#endif
>                 : "=r" (pc)
>                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> -                 "lr", "memory", "cc"
> +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> +                 FPREG_CLOBBER, "lr", "memory", "cc"
>                 );
>
>         bx_write_pc(pc, regs);
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

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Re: [PATCH v2 10/12] drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds

[Nick Desaulniers]

On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> The SMC calling convention designates R0-R7 as input registers in
> AArch32 mode, and this conflicts with the compiler's use of R7 as a
> frame pointer when building in Thumb2 mode. Generally, we don't enable
> the frame pointer, and GCC happily enables the -pg profiling hooks
> without them. However, Clang refuses, and errors out with the message
> below:
>
> drivers/firmware/arm_scmi/smc.c:152:2: error: write to reserved register 'R7'
>         arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
>         ^
> include/linux/arm-smccc.h:550:4: note: expanded from macro 'arm_smccc_1_1_invoke'
>                         arm_smccc_1_1_smc(__VA_ARGS__);                 \
>                         ^
> Let's just disable ftrace for the compilation unit when building this
> configuration.

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Would it make sense for clang not to warn in such cases? (i.e. write
to r7 for thumb when -fomit-frame-pointers is specified) If so, we can
file a feature request and at least add a link in the comment added in
the Makefile.

>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  drivers/firmware/arm_scmi/Makefile | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> index 1dcf123d64ab..52b9078bfe96 100644
> --- a/drivers/firmware/arm_scmi/Makefile
> +++ b/drivers/firmware/arm_scmi/Makefile
> @@ -11,3 +11,10 @@ scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>                     $(scmi-transport-y)
>  obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-module.o
>  obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o
> +
> +ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy)
> +# The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame
> +# pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling
> +# hooks are inserted via the -pg switch.
> +CFLAGS_REMOVE_smc.o += $(CC_FLAGS_FTRACE)
> +endif
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

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Re: [PATCH v2 11/12] ARM: cacheflush: avoid clobbering the frame pointer in Thumb2 mode

[Nick Desaulniers]

On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> Thumb2 uses R7 rather than R11 as the frame pointer, and even if we
> rarely use a frame pointer to begin with when building in Thumb2 mode,
> there are cases where it is required by the compiler (Clang when
> inserting profiling hooks via -pg)
>
> So let's preserve whichever register is considered the frame pointer
> depending on whether we are building for ARM or Thumb2, rather than
> preserving/restoring R11 explicitly.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/include/asm/cacheflush.h  | 7 ++++---
>  arch/arm/mach-exynos/mcpm-exynos.c | 7 ++++---
>  2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
> index e68fb879e4f9..5c4c49086ac6 100644
> --- a/arch/arm/include/asm/cacheflush.h
> +++ b/arch/arm/include/asm/cacheflush.h
> @@ -12,6 +12,7 @@
>  #include <asm/glue-cache.h>
>  #include <asm/shmparam.h>
>  #include <asm/cachetype.h>
> +#include <asm/opcodes.h>
>  #include <asm/outercache.h>
>
>  #define CACHE_COLOUR(vaddr)    ((vaddr & (SHMLBA - 1)) >> PAGE_SHIFT)
> @@ -454,7 +455,7 @@ static inline void __sync_cache_range_r(volatile void *p, size_t size)
>  #define v7_exit_coherency_flush(level) \
>         asm volatile( \
>         ".arch  armv7-a \n\t" \
> -       "stmfd  sp!, {fp, ip} \n\t" \
> +       "stmfd  sp!, {" FPREG_PRESERVE ", ip} \n\t" \
>         "mrc    p15, 0, r0, c1, c0, 0   @ get SCTLR \n\t" \
>         "bic    r0, r0, #"__stringify(CR_C)" \n\t" \
>         "mcr    p15, 0, r0, c1, c0, 0   @ set SCTLR \n\t" \
> @@ -465,8 +466,8 @@ static inline void __sync_cache_range_r(volatile void *p, size_t size)
>         "mcr    p15, 0, r0, c1, c0, 1   @ set ACTLR \n\t" \
>         "isb    \n\t" \
>         "dsb    \n\t" \
> -       "ldmfd  sp!, {fp, ip}" \
> -       : : : "r0","r1","r2","r3","r4","r5","r6","r7", \
> +       "ldmfd  sp!, {" FPREG_PRESERVE ", ip}" \
> +       : : : "r0","r1","r2","r3","r4","r5","r6", FPREG_CLOBBER, \
>               "r9","r10","lr","memory" )
>
>  void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,
> diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
> index cd861c57d5ad..0cebc008d877 100644
> --- a/arch/arm/mach-exynos/mcpm-exynos.c
> +++ b/arch/arm/mach-exynos/mcpm-exynos.c
> @@ -14,6 +14,7 @@
>  #include <asm/cputype.h>
>  #include <asm/cp15.h>
>  #include <asm/mcpm.h>
> +#include <asm/opcodes.h>
>  #include <asm/smp_plat.h>
>
>  #include "common.h"
> @@ -35,7 +36,7 @@ static bool secure_firmware __ro_after_init;
>   */
>  #define exynos_v7_exit_coherency_flush(level) \
>         asm volatile( \
> -       "stmfd  sp!, {fp, ip}\n\t"\
> +       "stmfd  sp!, {" FPREG_PRESERVE ", ip} \n\t" \
>         "mrc    p15, 0, r0, c1, c0, 0   @ get SCTLR\n\t" \
>         "bic    r0, r0, #"__stringify(CR_C)"\n\t" \
>         "mcr    p15, 0, r0, c1, c0, 0   @ set SCTLR\n\t" \
> @@ -50,10 +51,10 @@ static bool secure_firmware __ro_after_init;
>         "mcr    p15, 0, r0, c1, c0, 1   @ set ACTLR\n\t" \
>         "isb\n\t" \
>         "dsb\n\t" \
> -       "ldmfd  sp!, {fp, ip}" \
> +       "ldmfd  sp!, {" FPREG_PRESERVE ", ip}" \
>         : \
>         : "Ir" (pmu_base_addr + S5P_INFORM0) \
> -       : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", \
> +       : "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER, \
>           "r9", "r10", "lr", "memory")
>
>  static int exynos_cpu_powerup(unsigned int cpu, unsigned int cluster)
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

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Re: [PATCH v2 12/12] Revert "ARM: 9144/1: forbid ftrace with clang and thumb2_kernel"

[Nick Desaulniers]

On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> This reverts commit ecb108e3e3f7c692082b7c6fce41779c3835854a.
>
> Clang + Thumb2 with ftrace is now supported.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Thanks for all of the work that went into getting this fixed properly!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/arm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 3c6216f194f2..4ad7080bc17c 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -93,7 +93,7 @@ config ARM
>         select HAVE_FAST_GUP if ARM_LPAE
>         select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>         select HAVE_FUNCTION_GRAPH_TRACER
> -       select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)
> +       select HAVE_FUNCTION_TRACER if !XIP_KERNEL
>         select HAVE_FUTEX_CMPXCHG if FUTEX
>         select HAVE_GCC_PLUGINS
>         select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers

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Re: [PATCH v2 10/12] drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds

[Sudeep Holla]

On Mon, Jan 31, 2022 at 06:03:45PM +0100, Ard Biesheuvel wrote:
> The SMC calling convention designates R0-R7 as input registers in
> AArch32 mode, and this conflicts with the compiler's use of R7 as a
> frame pointer when building in Thumb2 mode. Generally, we don't enable
> the frame pointer, and GCC happily enables the -pg profiling hooks
> without them. However, Clang refuses, and errors out with the message
> below:
>
> drivers/firmware/arm_scmi/smc.c:152:2: error: write to reserved register 'R7'
>         arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
>         ^
> include/linux/arm-smccc.h:550:4: note: expanded from macro 'arm_smccc_1_1_invoke'
>                         arm_smccc_1_1_smc(__VA_ARGS__);                 \
>                         ^
> Let's just disable ftrace for the compilation unit when building this
> configuration.
>

Acked-by: Sudeep Holla <sudeep.holla@arm.com>

--
Regards,
Sudeep

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Ard Biesheuvel]

On Mon, 31 Jan 2022 at 19:31, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > Thumb2 code uses R7 as the frame pointer rather than R11, because the
> > opcodes to access it are generally shorter.
> >
> > This means that there are cases where we cannot simply add it to the
> > clobber list of an asm() block, but need to preserve/restore it
> > explicitly, or the compiler may complain in some cases (e.g., Clang
> > builds with ftrace enabled).
> >
> > Since R11 is not special in that case, clobber it instead, and use it to
> > preserve/restore the value of R7.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  arch/arm/include/asm/opcodes.h           | 14 ++++++++
> >  arch/arm/probes/kprobes/actions-common.c |  6 ++--
> >  arch/arm/probes/kprobes/actions-thumb.c  | 38 ++++++++++++++++----
> >  3 files changed, 48 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
> > index 38e3eabff5c3..9a6362408ea0 100644
> > --- a/arch/arm/include/asm/opcodes.h
> > +++ b/arch/arm/include/asm/opcodes.h
> > @@ -230,4 +230,18 @@ extern __u32 __opcode_to_mem_thumb32(__u32);
> >         ".short " __stringify(first) ", " __stringify(second) "\n\t"
> >  #endif
> >
> > +/*
> > + * Which register to preserve and which register can be clobbered in inline asm
> > + * that needs to be compatible with code that emits frame pointers.
> > + */
> > +#ifdef CONFIG_THUMB2_KERNEL
> > +#define FPREG_PRESERVE "r7"
> > +#define FPREG_CLOBBER  "r11"
> > +#define FPREG_PRESERVE_R7
> > +#else
> > +#define FPREG_PRESERVE "fp"
> > +#define FPREG_CLOBBER  "r7"
> > +#define FPREG_PRESERVE_R11
>
> I think you might be able to get away without FPREG_PRESERVE_R11 and
> even without FPREG_PRESERVE_R7. FPREG_PRESERVE_R11 is currently unused
> and FPREG_PRESERVE_R7 is synonymous with CONFIG_THUMB2_KERNEL at the
> moment (It doesn't look like patches 11 or 12 change that either).
> Looking at arch/arm/probes/kprobes/Makefile,
> arch/arm/probes/kprobes/actions-thumb.c is only built when
> CONFIG_THUMB2_KERNEL is enabled, so I don't think the #ifdefs are
> required; those `mov`s could be unguarded by the preprocessor?
>

You're quite right. I'll get rid of the macro and the CPP conditionals.

> > +#endif
> > +
> >  #endif /* __ASM_ARM_OPCODES_H */
> > diff --git a/arch/arm/probes/kprobes/actions-common.c b/arch/arm/probes/kprobes/actions-common.c
> > index 836aebe596cd..f0efe16e2fdb 100644
> > --- a/arch/arm/probes/kprobes/actions-common.c
> > +++ b/arch/arm/probes/kprobes/actions-common.c
> > @@ -84,7 +84,7 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
> >         register void *rfn asm("lr") = asi->insn_fn;
> >
> >         __asm__ __volatile__ (
> > -               "stmdb  sp!, {%[regs], r11}     \n\t"
> > +               "stmdb  sp!, {%[regs], " FPREG_PRESERVE "}\n\t"
> >                 "ldmia  %[regs], {r0-r12}       \n\t"
> >  #if __LINUX_ARM_ARCH__ >= 6
> >                 "blx    %[fn]                   \n\t"
> > @@ -96,10 +96,10 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
> >  #endif
> >                 "ldr    lr, [sp], #4            \n\t" /* lr = regs */
> >                 "stmia  lr, {r0-r12}            \n\t"
> > -               "ldr    r11, [sp], #4           \n\t"
> > +               "ldr    " FPREG_PRESERVE ", [sp], #4\n\t"
> >                 : [regs] "=r" (rregs), [fn] "=r" (rfn)
> >                 : "0" (rregs), "1" (rfn)
> > -               : "r0", "r2", "r3", "r4", "r5", "r6", "r7",
> > +               : "r0", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
> >                   "r8", "r9", "r10", "r12", "memory", "cc"
> >                 );
> >  }
> > diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
> > index 7884fcb81c26..873757326533 100644
> > --- a/arch/arm/probes/kprobes/actions-thumb.c
> > +++ b/arch/arm/probes/kprobes/actions-thumb.c
> > @@ -447,14 +447,20 @@ t16_emulate_loregs(probes_opcode_t insn,
> >
> >         __asm__ __volatile__ (
> >                 "msr    cpsr_fs, %[oldcpsr]     \n\t"
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    fp, r7                  \n\t"
> > +#endif
> >                 "ldmia  %[regs], {r0-r7}        \n\t"
> >                 "blx    %[fn]                   \n\t"
> >                 "stmia  %[regs], {r0-r7}        \n\t"
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    r7, fp                  \n\t"
> > +#endif
> >                 "mrs    %[newcpsr], cpsr        \n\t"
> >                 : [newcpsr] "=r" (newcpsr)
> >                 : [oldcpsr] "r" (oldcpsr), [regs] "r" (regs),
> >                   [fn] "r" (asi->insn_fn)
> > -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
> > +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
> >                   "lr", "memory", "cc"
> >                 );
> >
> > @@ -524,15 +530,21 @@ t16_emulate_push(probes_opcode_t insn,
> >                 struct arch_probes_insn *asi, struct pt_regs *regs)
> >  {
> >         __asm__ __volatile__ (
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    fp, r7                  \n\t"
> > +#endif
> >                 "ldr    r9, [%[regs], #13*4]    \n\t"
> >                 "ldr    r8, [%[regs], #14*4]    \n\t"
> >                 "ldmia  %[regs], {r0-r7}        \n\t"
> >                 "blx    %[fn]                   \n\t"
> >                 "str    r9, [%[regs], #13*4]    \n\t"
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    r7, fp                  \n\t"
> > +#endif
> >                 :
> >                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> > -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
> > -                 "lr", "memory", "cc"
> > +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r8", "r9",
> > +                 FPREG_CLOBBER, "lr", "memory", "cc"
> >                 );
> >  }
> >
> > @@ -558,15 +570,21 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
> >                 struct arch_probes_insn *asi, struct pt_regs *regs)
> >  {
> >         __asm__ __volatile__ (
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    fp, r7                  \n\t"
> > +#endif
> >                 "ldr    r9, [%[regs], #13*4]    \n\t"
> >                 "ldmia  %[regs], {r0-r7}        \n\t"
> >                 "blx    %[fn]                   \n\t"
> >                 "stmia  %[regs], {r0-r7}        \n\t"
> >                 "str    r9, [%[regs], #13*4]    \n\t"
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    r7, fp                  \n\t"
> > +#endif
> >                 :
> >                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> > -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> > -                 "lr", "memory", "cc"
> > +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> > +                 FPREG_CLOBBER, "lr", "memory", "cc"
> >                 );
> >  }
> >
> > @@ -577,15 +595,21 @@ t16_emulate_pop_pc(probes_opcode_t insn,
> >         register unsigned long pc asm("r8");
> >
> >         __asm__ __volatile__ (
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    fp, r7                  \n\t"
> > +#endif
> >                 "ldr    r9, [%[regs], #13*4]    \n\t"
> >                 "ldmia  %[regs], {r0-r7}        \n\t"
> >                 "blx    %[fn]                   \n\t"
> >                 "stmia  %[regs], {r0-r7}        \n\t"
> >                 "str    r9, [%[regs], #13*4]    \n\t"
> > +#ifdef FPREG_PRESERVE_R7
> > +               "mov    r7, fp                  \n\t"
> > +#endif
> >                 : "=r" (pc)
> >                 : [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> > -               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> > -                 "lr", "memory", "cc"
> > +               : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> > +                 FPREG_CLOBBER, "lr", "memory", "cc"
> >                 );
> >
> >         bx_write_pc(pc, regs);
> > --
> > 2.30.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

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Re: [PATCH v2 10/12] drivers/firmware/scmi: disable ftrace for Clang Thumb2 builds

[Ard Biesheuvel]

On Mon, 31 Jan 2022 at 19:37, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Mon, Jan 31, 2022 at 9:04 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > The SMC calling convention designates R0-R7 as input registers in
> > AArch32 mode, and this conflicts with the compiler's use of R7 as a
> > frame pointer when building in Thumb2 mode. Generally, we don't enable
> > the frame pointer, and GCC happily enables the -pg profiling hooks
> > without them. However, Clang refuses, and errors out with the message
> > below:
> >
> > drivers/firmware/arm_scmi/smc.c:152:2: error: write to reserved register 'R7'
> >         arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
> >         ^
> > include/linux/arm-smccc.h:550:4: note: expanded from macro 'arm_smccc_1_1_invoke'
> >                         arm_smccc_1_1_smc(__VA_ARGS__);                 \
> >                         ^
> > Let's just disable ftrace for the compilation unit when building this
> > configuration.
>
> Thanks for the patch!
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Would it make sense for clang not to warn in such cases? (i.e. write
> to r7 for thumb when -fomit-frame-pointers is specified) If so, we can
> file a feature request and at least add a link in the comment added in
> the Makefile.
>

This is a bit tricky. The ftrace code does not rely on a frame pointer
at all, which is why this is only an issue on Clang, as GCC happily
ignores the use of R7. On Clang, the frame pointer is mandatory with
-pg:

clang: error: invalid argument '-fomit-frame-pointer' not allowed with '-pg'

However, the way the unwinder is wired up in Linux means that only R7
is usable as an unwind anchor (apart from SP), which means that
clobbering R7 even temporarily is risky. Note that the same applies to
FP in places where we preserve/restore it currently. The fact that -pg
implies -fno-omit-frame-pointer on Clang makes this even worse,
because it means that all emitted unwind info will use R7 rather than
SP.

So it would help if we could relax the requirement for
-fno-omit-frame-pointer with -pg on ARM (provided that there is no
reason it is needed that I have missed). That would improve codegen as
well.

But it doesn't fix the underlying issue that clobbering R7 is risky,
and we should whether the clobber is sufficient to discourage the
compiler from using it as the unwind anchor. If this is the case, we
should probably pass -fno-unwind-tables to each function that uses R7
or FP in this manner.


> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  drivers/firmware/arm_scmi/Makefile | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> > index 1dcf123d64ab..52b9078bfe96 100644
> > --- a/drivers/firmware/arm_scmi/Makefile
> > +++ b/drivers/firmware/arm_scmi/Makefile
> > @@ -11,3 +11,10 @@ scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
> >                     $(scmi-transport-y)
> >  obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-module.o
> >  obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o
> > +
> > +ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy)
> > +# The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame
> > +# pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling
> > +# hooks are inserted via the -pg switch.
> > +CFLAGS_REMOVE_smc.o += $(CC_FLAGS_FTRACE)
> > +endif
> > --
> > 2.30.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Masami Hiramatsu]

On Mon, 31 Jan 2022 18:03:44 +0100
Ard Biesheuvel <ardb@kernel.org> wrote:

> Thumb2 code uses R7 as the frame pointer rather than R11, because the
> opcodes to access it are generally shorter.
> 
> This means that there are cases where we cannot simply add it to the
> clobber list of an asm() block, but need to preserve/restore it
> explicitly, or the compiler may complain in some cases (e.g., Clang
> builds with ftrace enabled).
> 
> Since R11 is not special in that case, clobber it instead, and use it to
> preserve/restore the value of R7.

Thanks Ard for fixing thumb2 issue!
BTW, have you build the kernel with CONFIG_KPROBES_SANITY_TEST=y?
It should check the backtrace from kprobe and kretprobe at boot time.

Thank you,

> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/arm/include/asm/opcodes.h           | 14 ++++++++
>  arch/arm/probes/kprobes/actions-common.c |  6 ++--
>  arch/arm/probes/kprobes/actions-thumb.c  | 38 ++++++++++++++++----
>  3 files changed, 48 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
> index 38e3eabff5c3..9a6362408ea0 100644
> --- a/arch/arm/include/asm/opcodes.h
> +++ b/arch/arm/include/asm/opcodes.h
> @@ -230,4 +230,18 @@ extern __u32 __opcode_to_mem_thumb32(__u32);
>  	".short " __stringify(first) ", " __stringify(second) "\n\t"
>  #endif
>  
> +/*
> + * Which register to preserve and which register can be clobbered in inline asm
> + * that needs to be compatible with code that emits frame pointers.
> + */
> +#ifdef CONFIG_THUMB2_KERNEL
> +#define FPREG_PRESERVE	"r7"
> +#define FPREG_CLOBBER	"r11"
> +#define FPREG_PRESERVE_R7
> +#else
> +#define FPREG_PRESERVE	"fp"
> +#define FPREG_CLOBBER	"r7"
> +#define FPREG_PRESERVE_R11
> +#endif
> +
>  #endif /* __ASM_ARM_OPCODES_H */
> diff --git a/arch/arm/probes/kprobes/actions-common.c b/arch/arm/probes/kprobes/actions-common.c
> index 836aebe596cd..f0efe16e2fdb 100644
> --- a/arch/arm/probes/kprobes/actions-common.c
> +++ b/arch/arm/probes/kprobes/actions-common.c
> @@ -84,7 +84,7 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
>  	register void *rfn asm("lr") = asi->insn_fn;
>  
>  	__asm__ __volatile__ (
> -		"stmdb	sp!, {%[regs], r11}	\n\t"
> +		"stmdb	sp!, {%[regs], " FPREG_PRESERVE "}\n\t"
>  		"ldmia	%[regs], {r0-r12}	\n\t"
>  #if __LINUX_ARM_ARCH__ >= 6
>  		"blx	%[fn]			\n\t"
> @@ -96,10 +96,10 @@ emulate_generic_r0_12_noflags(probes_opcode_t insn,
>  #endif
>  		"ldr	lr, [sp], #4		\n\t" /* lr = regs */
>  		"stmia	lr, {r0-r12}		\n\t"
> -		"ldr	r11, [sp], #4		\n\t"
> +		"ldr	" FPREG_PRESERVE ", [sp], #4\n\t"
>  		: [regs] "=r" (rregs), [fn] "=r" (rfn)
>  		: "0" (rregs), "1" (rfn)
> -		: "r0", "r2", "r3", "r4", "r5", "r6", "r7",
> +		: "r0", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
>  		  "r8", "r9", "r10", "r12", "memory", "cc"
>  		);
>  }
> diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
> index 7884fcb81c26..873757326533 100644
> --- a/arch/arm/probes/kprobes/actions-thumb.c
> +++ b/arch/arm/probes/kprobes/actions-thumb.c
> @@ -447,14 +447,20 @@ t16_emulate_loregs(probes_opcode_t insn,
>  
>  	__asm__ __volatile__ (
>  		"msr	cpsr_fs, %[oldcpsr]	\n\t"
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	fp, r7			\n\t"
> +#endif
>  		"ldmia	%[regs], {r0-r7}	\n\t"
>  		"blx	%[fn]			\n\t"
>  		"stmia	%[regs], {r0-r7}	\n\t"
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	r7, fp			\n\t"
> +#endif
>  		"mrs	%[newcpsr], cpsr	\n\t"
>  		: [newcpsr] "=r" (newcpsr)
>  		: [oldcpsr] "r" (oldcpsr), [regs] "r" (regs),
>  		  [fn] "r" (asi->insn_fn)
> -		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
> +		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", FPREG_CLOBBER,
>  		  "lr", "memory", "cc"
>  		);
>  
> @@ -524,15 +530,21 @@ t16_emulate_push(probes_opcode_t insn,
>  		struct arch_probes_insn *asi, struct pt_regs *regs)
>  {
>  	__asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	fp, r7			\n\t"
> +#endif
>  		"ldr	r9, [%[regs], #13*4]	\n\t"
>  		"ldr	r8, [%[regs], #14*4]	\n\t"
>  		"ldmia	%[regs], {r0-r7}	\n\t"
>  		"blx	%[fn]			\n\t"
>  		"str	r9, [%[regs], #13*4]	\n\t"
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	r7, fp			\n\t"
> +#endif
>  		:
>  		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
> -		  "lr", "memory", "cc"
> +		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r8", "r9",
> +		  FPREG_CLOBBER, "lr", "memory", "cc"
>  		);
>  }
>  
> @@ -558,15 +570,21 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
>  		struct arch_probes_insn *asi, struct pt_regs *regs)
>  {
>  	__asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	fp, r7			\n\t"
> +#endif
>  		"ldr	r9, [%[regs], #13*4]	\n\t"
>  		"ldmia	%[regs], {r0-r7}	\n\t"
>  		"blx	%[fn]			\n\t"
>  		"stmia	%[regs], {r0-r7}	\n\t"
>  		"str	r9, [%[regs], #13*4]	\n\t"
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	r7, fp			\n\t"
> +#endif
>  		:
>  		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> -		  "lr", "memory", "cc"
> +		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> +		  FPREG_CLOBBER, "lr", "memory", "cc"
>  		);
>  }
>  
> @@ -577,15 +595,21 @@ t16_emulate_pop_pc(probes_opcode_t insn,
>  	register unsigned long pc asm("r8");
>  
>  	__asm__ __volatile__ (
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	fp, r7			\n\t"
> +#endif
>  		"ldr	r9, [%[regs], #13*4]	\n\t"
>  		"ldmia	%[regs], {r0-r7}	\n\t"
>  		"blx	%[fn]			\n\t"
>  		"stmia	%[regs], {r0-r7}	\n\t"
>  		"str	r9, [%[regs], #13*4]	\n\t"
> +#ifdef FPREG_PRESERVE_R7
> +		"mov	r7, fp			\n\t"
> +#endif
>  		: "=r" (pc)
>  		: [regs] "r" (regs), [fn] "r" (asi->insn_fn)
> -		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r9",
> -		  "lr", "memory", "cc"
> +		: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r9",
> +		  FPREG_CLOBBER, "lr", "memory", "cc"
>  		);
>  
>  	bx_write_pc(pc, regs);
> -- 
> 2.30.2
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Ard Biesheuvel]

On Tue, 1 Feb 2022 at 14:18, Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Mon, 31 Jan 2022 18:03:44 +0100
> Ard Biesheuvel <ardb@kernel.org> wrote:
>
> > Thumb2 code uses R7 as the frame pointer rather than R11, because the
> > opcodes to access it are generally shorter.
> >
> > This means that there are cases where we cannot simply add it to the
> > clobber list of an asm() block, but need to preserve/restore it
> > explicitly, or the compiler may complain in some cases (e.g., Clang
> > builds with ftrace enabled).
> >
> > Since R11 is not special in that case, clobber it instead, and use it to
> > preserve/restore the value of R7.
>
> Thanks Ard for fixing thumb2 issue!

No problem. Although I'm still not 100% sure we can simply
preserve/restore the frame pointer like that. What is the expected
result when an exception occurs in the kprobes emulation code?

The main problem is that with unwind info unwinding, the stack pointer
and the frame pointer need to be mutually in sync, and with the
kprobes stack frames in the middle, this is no longer correct - the
emulated code is executed with the frame pointer value that was
captured when the probe was hit, by the stack has a couple of frames
added.

> BTW, have you build the kernel with CONFIG_KPROBES_SANITY_TEST=y?
> It should check the backtrace from kprobe and kretprobe at boot time.
>

Just checked, and those work fine.

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Masami Hiramatsu]

On Tue, 1 Feb 2022 15:05:25 +0100
Ard Biesheuvel <ardb@kernel.org> wrote:

> On Tue, 1 Feb 2022 at 14:18, Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > On Mon, 31 Jan 2022 18:03:44 +0100
> > Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > > Thumb2 code uses R7 as the frame pointer rather than R11, because the
> > > opcodes to access it are generally shorter.
> > >
> > > This means that there are cases where we cannot simply add it to the
> > > clobber list of an asm() block, but need to preserve/restore it
> > > explicitly, or the compiler may complain in some cases (e.g., Clang
> > > builds with ftrace enabled).
> > >
> > > Since R11 is not special in that case, clobber it instead, and use it to
> > > preserve/restore the value of R7.
> >
> > Thanks Ard for fixing thumb2 issue!
> 
> No problem. Although I'm still not 100% sure we can simply
> preserve/restore the frame pointer like that. What is the expected
> result when an exception occurs in the kprobes emulation code?

What kind of exception would you mean? If it is a synchronous
exception and can return to where the exception happens, the
all registers must be restored. So as long as it is restored
it is OK to me.

> The main problem is that with unwind info unwinding, the stack pointer
> and the frame pointer need to be mutually in sync, and with the
> kprobes stack frames in the middle, this is no longer correct - the
> emulated code is executed with the frame pointer value that was
> captured when the probe was hit, by the stack has a couple of frames
> added.
> 
> > BTW, have you build the kernel with CONFIG_KPROBES_SANITY_TEST=y?
> > It should check the backtrace from kprobe and kretprobe at boot time.
> >
> 
> Just checked, and those work fine.

Thank you for testing!

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

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Re: [PATCH v2 09/12] ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds

[Ard Biesheuvel]

On Wed, 2 Feb 2022 at 07:10, Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Tue, 1 Feb 2022 15:05:25 +0100
> Ard Biesheuvel <ardb@kernel.org> wrote:
>
> > On Tue, 1 Feb 2022 at 14:18, Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > >
> > > On Mon, 31 Jan 2022 18:03:44 +0100
> > > Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > > Thumb2 code uses R7 as the frame pointer rather than R11, because the
> > > > opcodes to access it are generally shorter.
> > > >
> > > > This means that there are cases where we cannot simply add it to the
> > > > clobber list of an asm() block, but need to preserve/restore it
> > > > explicitly, or the compiler may complain in some cases (e.g., Clang
> > > > builds with ftrace enabled).
> > > >
> > > > Since R11 is not special in that case, clobber it instead, and use it to
> > > > preserve/restore the value of R7.
> > >
> > > Thanks Ard for fixing thumb2 issue!
> >
> > No problem. Although I'm still not 100% sure we can simply
> > preserve/restore the frame pointer like that. What is the expected
> > result when an exception occurs in the kprobes emulation code?
>
> What kind of exception would you mean? If it is a synchronous
> exception and can return to where the exception happens, the
> all registers must be restored. So as long as it is restored
> it is OK to me.
>

So what should happen if a backtrace is triggered while the kprobes
emulation code is calling into a function?


> > The main problem is that with unwind info unwinding, the stack pointer
> > and the frame pointer need to be mutually in sync, and with the
> > kprobes stack frames in the middle, this is no longer correct - the
> > emulated code is executed with the frame pointer value that was
> > captured when the probe was hit, by the stack has a couple of frames
> > added.
> >
> > > BTW, have you build the kernel with CONFIG_KPROBES_SANITY_TEST=y?
> > > It should check the backtrace from kprobe and kretprobe at boot time.
> > >
> >
> > Just checked, and those work fine.
>
> Thank you for testing!
>
> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
>

Thanks!

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