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From 80db5b343bd44806881d400a8627cb526ffccee7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timo=20Ter=C3=A4s?= <timo.teras@iki.fi>
Date: Thu, 10 Nov 2011 09:36:44 +0200
Subject: [PATCH] libc/x86: fix stack unwinding and backtrace information
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
When compiled without framepointer, the DWARF-2 CFI data is required
for proper stack unwinding.
This patch adds the CFI information to:
* syscalls (so we get proper backtrace even for release builds)
* new thread stub function (so the backtrace is clean for user
created threads)
Also pads the signal return trampolines separate from other functions.
If CFI info was found for signal return code (which seems to happen if
it's located right next a valid function), it will not be recognized
as signal trampoline (gcc unwinder and gdb check first CFI info, and
only if it does not exists it compares the exact opcode sequence to
see if we are at signal return code block). This fixes a real crash
if thread is cancelled and the cancellation handler fails to detect the
signal return frame.
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
---
libc/sysdeps/linux/i386/bits/syscalls.h | 13 +++++++++----
libc/sysdeps/linux/i386/clone.S | 17 +++++++++++++++++
libc/sysdeps/linux/i386/sigaction.c | 4 ++++
3 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/libc/sysdeps/linux/i386/bits/syscalls.h b/libc/sysdeps/linux/i386/bits/syscalls.h
index eeafb3a..47d0b4c 100644
--- a/libc/sysdeps/linux/i386/bits/syscalls.h
+++ b/libc/sysdeps/linux/i386/bits/syscalls.h
@@ -13,6 +13,7 @@
#ifndef __ASSEMBLER__
#include <errno.h>
+#include <common/sysdep.h>
#define INTERNAL_SYSCALL_NCS(name, err, nr, args...) \
({ \
@@ -71,6 +72,8 @@ __asm__ (
".if 1 - \\name\n\t" /* if reg!=ebx... */
".if 2 - \\name\n\t" /* if reg can't be clobbered... */
"pushl %ebx\n\t" /* save ebx on stack */
+ CFI_ADJUST_CFA_OFFSET(4) "\n\t"
+ CFI_REL_OFFSET(ebx, 0) "\n\t"
".else\n\t"
"xchgl \\reg, %ebx\n\t" /* else save ebx in reg, and load reg to ebx */
".endif\n\t"
@@ -89,6 +92,8 @@ __asm__ (
".if 1 - \\name\n\t"
".if 2 - \\name\n\t" /* if reg can't be clobbered... */
"popl %ebx\n\t" /* restore ebx from stack */
+ CFI_ADJUST_CFA_OFFSET(-4) "\n\t"
+ CFI_RESTORE(ebx) "\n\t"
".else\n\t"
"xchgl \\reg, %ebx\n\t" /* else restore ebx from reg */
".endif\n\t"
@@ -106,7 +111,7 @@ __asm__ (
#define LOADARGS_3 LOADARGS_1
#define LOADARGS_4 LOADARGS_1
#define LOADARGS_5 LOADARGS_1
-#define LOADARGS_6 LOADARGS_1 "push %%ebp\n\t" "movl %7, %%ebp\n\t"
+#define LOADARGS_6 LOADARGS_1 "push %%ebp\n\t" CFI_ADJUST_CFA_OFFSET(4) "\n\t" CFI_REL_OFFSET(ebp, 0) "\n\t" "movl %7, %%ebp\n\t"
#define RESTOREARGS_0
#define RESTOREARGS_1 "bpopl .L__X'%k2, %k2\n\t"
@@ -114,7 +119,7 @@ __asm__ (
#define RESTOREARGS_3 RESTOREARGS_1
#define RESTOREARGS_4 RESTOREARGS_1
#define RESTOREARGS_5 RESTOREARGS_1
-#define RESTOREARGS_6 "pop %%ebp\n\t" RESTOREARGS_1
+#define RESTOREARGS_6 "pop %%ebp\n\t" CFI_ADJUST_CFA_OFFSET(-4) "\n\t" CFI_RESTORE(ebp) "\n\t" RESTOREARGS_1
#define ASMFMT_0()
/* "acdSD" constraint would work too, but "SD" would use esi/edi and cause
@@ -162,7 +167,7 @@ __asm__ (
#define LOADARGS_3
#define LOADARGS_4
#define LOADARGS_5
-#define LOADARGS_6 "push %%ebp\n\t" "movl %7, %%ebp\n\t"
+#define LOADARGS_6 "push %%ebp\n\t" CFI_ADJUST_CFA_OFFSET(4) "\n\t" CFI_REL_OFFSET(ebp, 0) "\n\t" "movl %7, %%ebp\n\t"
#define RESTOREARGS_0
#define RESTOREARGS_1
@@ -170,7 +175,7 @@ __asm__ (
#define RESTOREARGS_3
#define RESTOREARGS_4
#define RESTOREARGS_5
-#define RESTOREARGS_6 "pop %%ebp\n\t"
+#define RESTOREARGS_6 "pop %%ebp\n\t" CFI_ADJUST_CFA_OFFSET(-4) "\n\t" CFI_RESTORE(ebp) "\n\t"
#define ASMFMT_0()
#define ASMFMT_1(arg1) \
diff --git a/libc/sysdeps/linux/i386/clone.S b/libc/sysdeps/linux/i386/clone.S
index a7de3fe..cf6cd35 100644
--- a/libc/sysdeps/linux/i386/clone.S
+++ b/libc/sysdeps/linux/i386/clone.S
@@ -25,6 +25,7 @@
#define _ERRNO_H 1
#include <bits/errno.h>
+#include <sysdep.h>
#include <sys/syscall.h>
/* int clone(int (*fn)(void *arg), void *child_stack, int flags, void *arg,
@@ -45,6 +46,7 @@
.global clone
.type clone,%function
clone:
+ cfi_startproc;
/* Sanity check arguments. */
movl $-EINVAL,%eax
@@ -86,17 +88,28 @@ clone:
/* Do the system call */
pushl %ebx
+ cfi_adjust_cfa_offset (4)
pushl %esi
+ cfi_adjust_cfa_offset (4)
pushl %edi
+ cfi_adjust_cfa_offset (4)
+
movl TLS+12(%esp),%esi
+ cfi_rel_offset (esi, 4)
movl PTID+12(%esp),%edx
movl FLAGS+12(%esp),%ebx
+ cfi_rel_offset (ebx, 8)
movl CTID+12(%esp),%edi
+ cfi_rel_offset (edi, 0)
movl $__NR_clone,%eax
#ifdef RESET_PID
/* Remember the flag value. */
movl %ebx, (%ecx)
#endif
+ /* End FDE now, because in the child the unwind info will be
+ wrong. */
+ cfi_endproc
+
int $0x80
popl %edi
popl %esi
@@ -108,6 +121,9 @@ clone:
ret
.Lthread_start:
+ cfi_startproc;
+ /* Clearing frame pointer is insufficient, use CFI. */
+ cfi_undefined (eip);
/* Note: %esi is zero. */
movl %esi,%ebp /* terminate the stack frame */
call *%ebx
@@ -120,6 +136,7 @@ clone:
movl %eax, %ebx
movl $__NR_exit, %eax
int $0x80
+ cfi_endproc;
/* Need to indirect jump to syscall error
* or we end up with TEXTREL's
diff --git a/libc/sysdeps/linux/i386/sigaction.c b/libc/sysdeps/linux/i386/sigaction.c
index de0c75d..f9af3f7 100644
--- a/libc/sysdeps/linux/i386/sigaction.c
+++ b/libc/sysdeps/linux/i386/sigaction.c
@@ -112,6 +112,9 @@ libc_hidden_weak(sigaction)
#define RESTORE2(name, syscall) \
__asm__ ( \
".text\n" \
+ ".align 8\n" \
+ " nop\n" \
+ ".align 16\n" \
"__" #name ":\n" \
" movl $" #syscall ", %eax\n" \
" int $0x80\n" \
@@ -128,6 +131,7 @@ RESTORE(restore_rt, __NR_rt_sigreturn)
# define RESTORE2(name, syscall) \
__asm__ ( \
".text\n" \
+ ".align 8\n" \
"__" #name ":\n" \
" popl %eax\n" \
" movl $" #syscall ", %eax\n" \
--
1.7.7
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