[PATCH v2 16/36] linux-user/arm: Add vdso and use it for rt_sigreturn

[Richard Henderson <richard.henderson@linaro.org>]

Building of the vdsos are not actually wired up to anything, since
we require a cross-compiler.  Just check in the files for now.

The thumb vdso will only be used for m-profile, as all of our
a-profile cpus support arm mode.

Cc: qemu-arm@nongnu.org
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/arm/signal.c       |  83 +++-----------
 linux-user/elfload.c          |  24 ++++
 linux-user/arm/Makefile.vdso  |  17 +++
 linux-user/arm/meson.build    |  18 +++
 linux-user/arm/vdso-arm-be.so | Bin 0 -> 5648 bytes
 linux-user/arm/vdso-arm-le.so | Bin 0 -> 5648 bytes
 linux-user/arm/vdso-thm-be.so | Bin 0 -> 5620 bytes
 linux-user/arm/vdso-thm-le.so | Bin 0 -> 5620 bytes
 linux-user/arm/vdso.S         | 209 ++++++++++++++++++++++++++++++++++
 linux-user/arm/vdso.ld        |  74 ++++++++++++
 10 files changed, 359 insertions(+), 66 deletions(-)
 create mode 100644 linux-user/arm/Makefile.vdso
 create mode 100755 linux-user/arm/vdso-arm-be.so
 create mode 100755 linux-user/arm/vdso-arm-le.so
 create mode 100755 linux-user/arm/vdso-thm-be.so
 create mode 100755 linux-user/arm/vdso-thm-le.so
 create mode 100644 linux-user/arm/vdso.S
 create mode 100644 linux-user/arm/vdso.ld

diff --git a/linux-user/arm/signal.c b/linux-user/arm/signal.c
index 565a355fc4..8edc1b1373 100644
--- a/linux-user/arm/signal.c
+++ b/linux-user/arm/signal.c
@@ -102,40 +102,6 @@ struct rt_sigframe
     abi_ulong retcode[4];
 };
 
-/*
- * For ARM syscalls, we encode the syscall number into the instruction.
- */
-#define SWI_SYS_SIGRETURN       (0xef000000|(TARGET_NR_sigreturn + ARM_SYSCALL_BASE))
-#define SWI_SYS_RT_SIGRETURN    (0xef000000|(TARGET_NR_rt_sigreturn + ARM_SYSCALL_BASE))
-
-/*
- * For Thumb syscalls, we pass the syscall number via r7.  We therefore
- * need two 16-bit instructions.
- */
-#define SWI_THUMB_SIGRETURN     (0xdf00 << 16 | 0x2700 | (TARGET_NR_sigreturn))
-#define SWI_THUMB_RT_SIGRETURN  (0xdf00 << 16 | 0x2700 | (TARGET_NR_rt_sigreturn))
-
-static const abi_ulong retcodes[4] = {
-        SWI_SYS_SIGRETURN,      SWI_THUMB_SIGRETURN,
-        SWI_SYS_RT_SIGRETURN,   SWI_THUMB_RT_SIGRETURN
-};
-
-/*
- * Stub needed to make sure the FD register (r9) contains the right
- * value.
- */
-static const unsigned long sigreturn_fdpic_codes[3] = {
-    0xe59fc004, /* ldr r12, [pc, #4] to read function descriptor */
-    0xe59c9004, /* ldr r9, [r12, #4] to setup GOT */
-    0xe59cf000  /* ldr pc, [r12] to jump into restorer */
-};
-
-static const unsigned long sigreturn_fdpic_thumb_codes[3] = {
-    0xc008f8df, /* ldr r12, [pc, #8] to read function descriptor */
-    0x9004f8dc, /* ldr r9, [r12, #4] to setup GOT */
-    0xf000f8dc  /* ldr pc, [r12] to jump into restorer */
-};
-
 static inline int valid_user_regs(CPUARMState *regs)
 {
     return 1;
@@ -188,9 +154,10 @@ setup_return(CPUARMState *env, struct target_sigaction *ka,
     abi_ulong handler = 0;
     abi_ulong handler_fdpic_GOT = 0;
     abi_ulong retcode;
-
-    int thumb;
-    int is_fdpic = info_is_fdpic(((TaskState *)thread_cpu->opaque)->info);
+    bool thumb;
+    bool is_fdpic = info_is_fdpic(((TaskState *)thread_cpu->opaque)->info);
+    uint32_t cpsr;
+    int idx;
 
     if (is_fdpic) {
         /* In FDPIC mode, ka->_sa_handler points to a function
@@ -208,7 +175,7 @@ setup_return(CPUARMState *env, struct target_sigaction *ka,
 
     thumb = handler & 1;
 
-    uint32_t cpsr = cpsr_read(env);
+    cpsr = cpsr_read(env);
 
     cpsr &= ~CPSR_IT;
     if (thumb) {
@@ -222,39 +189,23 @@ setup_return(CPUARMState *env, struct target_sigaction *ka,
         cpsr &= ~CPSR_E;
     }
 
+    /* Our vdso default_sigreturn label is a table of entry points. */
+    idx = is_fdpic * 2 + ((ka->sa_flags & TARGET_SA_SIGINFO) != 0);
+    retcode = default_sigreturn + idx * 16;
+
+    /*
+     * Put the sigreturn code on the stack no matter which return
+     * mechanism we use in order to remain ABI compliant.
+     */
+    memcpy(rc, g2h_untagged(retcode & ~1), 16);
+
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         if (is_fdpic) {
-            /* For FDPIC we ensure that the restorer is called with a
-             * correct r9 value.  For that we need to write code on
-             * the stack that sets r9 and jumps back to restorer
-             * value.
-             */
-            if (thumb) {
-                __put_user(sigreturn_fdpic_thumb_codes[0], rc);
-                __put_user(sigreturn_fdpic_thumb_codes[1], rc + 1);
-                __put_user(sigreturn_fdpic_thumb_codes[2], rc + 2);
-                __put_user((abi_ulong)ka->sa_restorer, rc + 3);
-            } else {
-                __put_user(sigreturn_fdpic_codes[0], rc);
-                __put_user(sigreturn_fdpic_codes[1], rc + 1);
-                __put_user(sigreturn_fdpic_codes[2], rc + 2);
-                __put_user((abi_ulong)ka->sa_restorer, rc + 3);
-            }
-
-            retcode = rc_addr + thumb;
+            /* Place the function descriptor in slot 3. */
+            __put_user((abi_ulong)ka->sa_restorer, rc + 3);
         } else {
             retcode = ka->sa_restorer;
         }
-    } else {
-        unsigned int idx = thumb;
-
-        if (ka->sa_flags & TARGET_SA_SIGINFO) {
-            idx += 2;
-        }
-
-        __put_user(retcodes[idx], rc);
-
-        retcode = rc_addr + thumb;
     }
 
     env->regs[0] = usig;
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 8088828f5f..40cc79b129 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -517,6 +517,30 @@ static const char *get_elf_platform(void)
 #undef END
 }
 
+#ifdef TARGET_WORDS_BIGENDIAN
+# include "vdso-arm-be.c.inc"
+# include "vdso-thm-be.c.inc"
+#else
+# include "vdso-arm-le.c.inc"
+# include "vdso-thm-le.c.inc"
+#endif
+
+static const VdsoImageInfo *vdso_image_info(void)
+{
+    ARMCPU *cpu = ARM_CPU(thread_cpu);
+
+    /*
+     * The only cpus we support that do *not* have arm mode are m-profile.
+     * It's not really possible to run Linux on these, but this config is
+     * useful for testing gcc.  In any case, choose the vdso image that
+     * will work for the target cpu.
+     */
+    return (cpu_isar_feature(aa32_a32, cpu)
+            ? &vdso_arm_image_info
+            : &vdso_thm_image_info);
+}
+#define vdso_image_info vdso_image_info
+
 #else
 /* 64 bit ARM definitions */
 #define ELF_START_MMAP 0x80000000
diff --git a/linux-user/arm/Makefile.vdso b/linux-user/arm/Makefile.vdso
new file mode 100644
index 0000000000..89da6f91ae
--- /dev/null
+++ b/linux-user/arm/Makefile.vdso
@@ -0,0 +1,17 @@
+CROSS_CC ?= arm-linux-gnueabihf-gcc
+LDFLAGS := -nostdlib -shared -Wl,-T,vdso.ld \
+	   -Wl,-h,linux-vdso.so.1 -Wl,--hash-style=sysv -Wl,--build-id=sha1
+
+all: vdso-arm-le.so vdso-arm-be.so vdso-thm-le.so vdso-thm-be.so
+
+vdso-arm-le.so: vdso.S vdso.ld Makefile.vdso
+	$(CROSS_CC) $(LDFLAGS) -mlittle-endian -marm vdso.S -o $@
+
+vdso-arm-be.so: vdso.S vdso.ld Makefile.vdso
+	$(CROSS_CC) $(LDFLAGS) -mbig-endian -marm vdso.S -o $@
+
+vdso-thm-le.so: vdso.S vdso.ld Makefile.vdso
+	$(CROSS_CC) $(LDFLAGS) -mlittle-endian -mthumb vdso.S -o $@
+
+vdso-thm-be.so: vdso.S vdso.ld Makefile.vdso
+	$(CROSS_CC) $(LDFLAGS) -mbig-endian -mthumb vdso.S -o $@
diff --git a/linux-user/arm/meson.build b/linux-user/arm/meson.build
index 5a93c925cf..66072411d6 100644
--- a/linux-user/arm/meson.build
+++ b/linux-user/arm/meson.build
@@ -5,3 +5,21 @@ syscall_nr_generators += {
                    arguments: [ meson.current_source_dir() / 'syscallhdr.sh', '@INPUT@', '@OUTPUT@', '@EXTRA_ARGS@' ],
                    output: '@BASENAME@_nr.h')
 }
+
+# ??? There does not seem to be a way to do
+#   when: ['TARGET_ARM', !'TARGET_WORDS_BIGENDIAN']
+# so we'd need to add TARGET_WORDS_LITTLEENDIAN.
+# In the meantime, build both files for arm and armeb.
+
+gen = [
+  gen_vdso.process('vdso-arm-be.so',
+                   extra_args: ['-s', 'sigreturn_codes', '-p', 'vdso_arm']),
+  gen_vdso.process('vdso-arm-le.so',
+                   extra_args: ['-s', 'sigreturn_codes', '-p', 'vdso_arm']),
+  gen_vdso.process('vdso-thm-be.so',
+                   extra_args: ['-s', 'sigreturn_codes', '-p', 'vdso_thm']),
+  gen_vdso.process('vdso-thm-le.so',
+                   extra_args: ['-s', 'sigreturn_codes', '-p', 'vdso_thm']),
+]
+
+linux_user_ss.add(when: 'TARGET_ARM', if_true: gen)
diff --git a/linux-user/arm/vdso-arm-be.so b/linux-user/arm/vdso-arm-be.so
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diff --git a/linux-user/arm/vdso.S b/linux-user/arm/vdso.S
new file mode 100644
index 0000000000..1831b29efc
--- /dev/null
+++ b/linux-user/arm/vdso.S
@@ -0,0 +1,209 @@
+/*
+ * arm linux replacement vdso.
+ *
+ * Copyright 2021 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <asm/unistd.h>
+
+	.text
+	.eabi_attribute Tag_FP_arch, 0
+
+#ifdef __thumb__
+	.thumb
+	.arch	armv7-m
+	.eabi_attribute Tag_ARM_ISA_use, 0
+	.eabi_attribute Tag_CPU_arch, 13 /* TAG_CPU_ARCH_V7_M */
+
+.macro	raw_syscall n
+	.ifne \n < 0x100
+	mov	r7, #\n
+	.else
+	ldr	r7, =\n
+	.endif
+	swi	#0
+.endm
+
+.macro	fdpic_thunk ofs
+	ldr	r3, [sp, #\ofs]
+	ldmia	r2, {r2, r3}
+	mov	r9, r3
+	bx	r2
+.endm
+
+#else
+	.arm
+	.arch	armv4t
+	.eabi_attribute Tag_THUMB_ISA_use, 0
+
+.macro	raw_syscall n
+	.ifne \n < 0x100
+	mov	r7, #\n
+	.else
+	mov	r7, #(\n & 0xff)
+	orr	r7, r7, #(\n & 0xff00)
+	.endif
+	svc	#(\n | __NR_OABI_SYSCALL_BASE)
+.endm
+
+.macro	fdpic_thunk ofs
+	ldr	r3, [sp, #\ofs]
+	ldmia	r3, {r3, r9}
+	bx	r3
+.endm
+
+#endif
+
+.macro	FUNC name
+	.globl	\name
+	.type	\name, %function
+#ifdef __thumb__
+	.thumb_func
+#endif
+\name:
+.endm
+
+.macro	ENDF name
+	.size	\name, . - \name
+.endm
+
+/*
+ * We must save/restore r7 for the EABI syscall number.
+ * While we're doing that, we might as well save LR to get a free return,
+ * and a branch that is interworking back to ARMv5.
+ */
+
+.macro syscall n
+	.cfi_startproc
+	push	{r7, lr}
+	.cfi_adjust_cfa_offset 8
+	.cfi_offset r7, -8
+	.cfi_offset lr, -4
+	raw_syscall \n
+	pop	{r7, pc}
+	.cfi_endproc
+.endm
+
+FUNC __vdso_clock_gettime
+	syscall	__NR_clock_gettime
+ENDF __vdso_clock_gettime
+
+FUNC __vdso_clock_gettime64
+	syscall	__NR_clock_gettime64
+ENDF __vdso_clock_gettime64
+
+FUNC __vdso_clock_getres
+	syscall	__NR_clock_getres
+ENDF __vdso_clock_getres
+
+FUNC __vdso_gettimeofday
+	syscall	__NR_gettimeofday
+ENDF __vdso_gettimeofday
+
+
+/*
+ * We, like the real kernel, use a table of sigreturn trampolines.
+ * Unlike the real kernel, we do not attempt to pack this into as
+ * few bytes as possible -- simply use 16 bytes per slot.
+ *
+ * Within each slot, use the exact same code sequence as the kernel,
+ * lest we trip up someone doing code inspection.
+ */
+
+/* offsetof(struct sigframe, retcode[3]) */
+#define SIGFRAME_RC3_OFFSET     756
+#define RT_SIGFRAME_RC3_OFFSET  884
+
+.macro	slot n
+	.balign	16
+	.org	sigreturn_codes + 16 * \n
+.endm
+
+/*
+ * Start the unwind info at least one instruction before the signal
+ * trampoline, because the unwinder will assume we are returning
+ * after a call site.
+ */
+	.cfi_startproc simple
+	.cfi_signal_frame
+	.cfi_return_column 15
+
+	.cfi_def_cfa	sp, 32 + 64
+	.cfi_offset	r0, -16 * 4
+	.cfi_offset	r1, -15 * 4
+	.cfi_offset	r2, -14 * 4
+	.cfi_offset	r3, -13 * 4
+	.cfi_offset	r4, -12 * 4
+	.cfi_offset	r5, -11 * 4
+	.cfi_offset	r6, -10 * 4
+	.cfi_offset	r7, -9 * 4
+	.cfi_offset	r8, -8 * 4
+	.cfi_offset	r9, -7 * 4
+	.cfi_offset	r10, -6 * 4
+	.cfi_offset	r11, -5 * 4
+	.cfi_offset	r12, -4 * 4
+	.cfi_offset	r13, -3 * 4
+	.cfi_offset	r14, -2 * 4
+	.cfi_offset	r15, -1 * 4
+
+	nop
+
+	.balign	16
+FUNC sigreturn_codes
+	/* [EO]ABI sigreturn */
+	slot	0
+	raw_syscall __NR_sigreturn
+
+	.cfi_def_cfa_offset 160 + 64
+
+	/* [EO]ABI rt_sigreturn */
+	slot	1
+	raw_syscall __NR_rt_sigreturn
+
+	.cfi_endproc
+
+	.macro cfi_fdpic_pc ofs
+	/*
+	 * fd = *(r13 + ofs)
+         * pc = *fd
+	 *
+	 * DW_CFA_expression lr (14), length (5),
+	 *   DW_OP_breg13, ofs, DW_OP_deref, DW_OP_deref
+         */
+	.cfi_escape 0x10, 14, 5, 0x7d, (\ofs & 0x7f) + 0x80, (\ofs >> 7), 0x06, 0x06
+	.endm
+
+	.macro cfi_fdpic_r9 ofs
+	/*
+	 * fd = *(r13 + ofs)
+         * r9 = *(fd + 4)
+	 *
+	 * DW_CFA_expression r9, length (7),
+	 *   DW_OP_breg13, ofs, DW_OP_deref,
+	 *   DW_OP_plus_uconst, 4, DW_OP_deref
+         */
+	.cfi_escape 0x10, 9, 7, 0x7d, (\ofs & 0x7f) + 0x80, (\ofs >> 7), 0x06, 0x23, 4, 0x06
+	.endm
+
+	/* FDPIC sigreturn */
+	.cfi_startproc
+	cfi_fdpic_pc SIGFRAME_RC3_OFFSET
+	cfi_fdpic_r9 SIGFRAME_RC3_OFFSET
+
+	slot	2
+	fdpic_thunk SIGFRAME_RC3_OFFSET
+	.cfi_endproc
+
+	/* FDPIC rt_sigreturn */
+	.cfi_startproc
+	cfi_fdpic_pc RT_SIGFRAME_RC3_OFFSET
+	cfi_fdpic_r9 RT_SIGFRAME_RC3_OFFSET
+
+	slot	3
+	fdpic_thunk RT_SIGFRAME_RC3_OFFSET
+	.cfi_endproc
+
+	.balign	16
+ENDF sigreturn_codes
diff --git a/linux-user/arm/vdso.ld b/linux-user/arm/vdso.ld
new file mode 100644
index 0000000000..3bddef97a5
--- /dev/null
+++ b/linux-user/arm/vdso.ld
@@ -0,0 +1,74 @@
+/*
+ * Linker script for linux arm replacement vdso.
+ *
+ * Copyright 2021 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+VERSION {
+        LINUX_2.6 {
+        global:
+                __vdso_clock_gettime;
+                __vdso_gettimeofday;
+                __vdso_clock_getres;
+                __vdso_clock_gettime64;
+
+        local: *;
+        };
+}
+
+
+PHDRS {
+        phdr            PT_PHDR         FLAGS(4) PHDRS;
+        data            PT_LOAD         FLAGS(6) FILEHDR PHDRS;
+        text            PT_LOAD         FLAGS(5);
+        dynamic         PT_DYNAMIC      FLAGS(4);
+        eh_frame_hdr    PT_GNU_EH_FRAME;
+        note            PT_NOTE         FLAGS(4);
+}
+
+SECTIONS {
+        /*
+         * We can't prelink to any address without knowing something about
+         * the virtual memory space of the host, since that leaks over into
+         * the available memory space of the guest.
+         */
+        . = SIZEOF_HEADERS;
+
+        /*
+         * The following, including the FILEHDRS and PHDRS, are modified
+         * when we relocate the binary.  We want them to be initially
+         * writable for the relocation; we'll force them read-only after.
+         */
+        .note           : { *(.note*) }         :data :note
+        .dynamic        : { *(.dynamic) }       :data :dynamic
+        .dynsym         : { *(.dynsym) }        :data
+        /*
+         * There ought not be any real read-write data.
+         * But since we manipulated the segment layout,
+         * we have to put these sections somewhere.
+         */
+        .data           : {
+                *(.data*)
+                *(.sdata*)
+                *(.got.plt) *(.got)
+                *(.gnu.linkonce.d.*)
+                *(.bss*)
+                *(.dynbss*)
+                *(.gnu.linkonce.b.*)
+        }
+
+        .rodata         : { *(.rodata*) }
+        .hash           : { *(.hash) }
+        .gnu.hash       : { *(.gnu.hash) }
+        .dynstr         : { *(.dynstr) }
+        .gnu.version    : { *(.gnu.version) }
+        .gnu.version_d  : { *(.gnu.version_d) }
+        .gnu.version_r  : { *(.gnu.version_r) }
+        .eh_frame_hdr   : { *(.eh_frame_hdr) }  :data :eh_frame_hdr
+        .eh_frame       : { *(.eh_frame) }      :data
+
+        . = ALIGN(4096);
+        .text           : { *(.text*) }         :text
+}
-- 
2.25.1