https://bugs.kde.org/show_bug.cgi?id=368120
Bug ID: 368120
Summary: x86_linux asm _start functions do not keep 16-byte
aligned stack pointer
Product: valgrind
Version: 3.11.0
Platform: Android
OS: other
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: c...@google.com
When valgrind is optimized by clang/llvm for x86 targets, clang/llvm requires
16-byte aligned stack pointers from the caller. The valgrind assembly functions
_start, vgModuleLocal_call_on_new_stack_0_1, and do_syscall_clone_x86_linux do
not keep stack pointer aligned before calling other functions.
This is working with gcc because it does not require such stack pointer
alignment.
When compiled with clang/llvm, memcheck aborted with segmentation fault.
The following diff should fixed the problem for Android x86 target:
@@ -2925,12 +2925,13 @@ asm("\n"
"\tmovl $vgPlain_interim_stack, %eax\n"
"\taddl $"VG_STRINGIFY(VG_STACK_GUARD_SZB)", %eax\n"
"\taddl $"VG_STRINGIFY(VG_DEFAULT_STACK_ACTIVE_SZB)", %eax\n"
+ /* allocate at least 16 bytes on the new stack, and aligned */
"\tsubl $16, %eax\n"
"\tandl $~15, %eax\n"
/* install it, and collect the original one */
"\txchgl %eax, %esp\n"
/* call _start_in_C_linux, passing it the startup %esp */
- "\tpushl %eax\n"
+ "\tmovl %eax, (%esp)\n"
"\tcall _start_in_C_linux\n"
"\thlt\n"
".previous\n"
diff --git a/coregrind/m_syswrap/syswrap-x86-linux.c
b/coregrind/m_syswrap/syswrap-x86-linux.c
index 24d7dc1..233886d 100644
--- a/coregrind/m_syswrap/syswrap-x86-linux.c
+++ b/coregrind/m_syswrap/syswrap-x86-linux.c
@@ -83,8 +83,9 @@ asm(
".globl vgModuleLocal_call_on_new_stack_0_1\n"
"vgModuleLocal_call_on_new_stack_0_1:\n"
" movl %esp, %esi\n" // remember old stack pointer
-" movl 4(%esi), %esp\n" // set stack
-" pushl 16(%esi)\n" // arg1 to stack
+" movl 4(%esi), %esp\n" // set stack, assume %esp is now 16-byte aligned
+" subl $12, %esp\n" // skip 12 bytes
+" pushl 16(%esi)\n" // arg1 to stack, %esp is 16-byte aligned
" pushl 8(%esi)\n" // retaddr to stack
" pushl 12(%esi)\n" // f to stack
" movl $0, %eax\n" // zero all GP regs
@@ -150,7 +151,8 @@ asm(
" movl 4+"FSZ"(%esp), %ecx\n" /* syscall arg2: child stack */
" movl 12+"FSZ"(%esp), %ebx\n" /* fn arg */
" movl 0+"FSZ"(%esp), %eax\n" /* fn */
-" lea -8(%ecx), %ecx\n" /* make space on stack */
+" andl $-16, %ecx\n" /* align to 16-byte */
+" lea -20(%ecx), %ecx\n" /* allocate 16*n+4 bytes on stack
*/
" movl %ebx, 4(%ecx)\n" /* fn arg */
" movl %eax, 0(%ecx)\n" /* fn */
@@ -165,7 +167,7 @@ asm(
" jnz 1f\n"
/* CHILD - call thread function */
-" popl %eax\n"
+" popl %eax\n" /* child %esp is 16-byte aligned
*/
" call *%eax\n" /* call fn */
/* exit with result */
Reproducible: Always
Steps to Reproduce:
1. Build valgrind with clang/llvm for x86 linux
2. Run valgrind to debug a 32-bit x86 program
Actual Results:
Segmentation fault in x86 32-bit memcheck.
See Android patch in https://android-review.googlesource.com/#/c/264837
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