https://llvm.org/bugs/show_bug.cgi?id=27183
Bug ID: 27183
Summary: __attribute__((force_align_arg_pointer)) with __asm__
causes segfault
Product: clang
Version: 3.8
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangbugs at nondot.org
Reporter: cjhopman at gmail.com
CC: llvm-bugs at lists.llvm.org
Classification: Unclassified
Created attachment 16149
--> https://llvm.org/bugs/attachment.cgi?id=16149&action=edit
Repro code.
This code:
__attribute__((noinline)) int use_sa(int* sa) {
return *sa;
}
__attribute__((force_align_arg_pointer))
int doit() {
int sa;
long res;
__asm__ __volatile__(
"nop"
: "=a" (res)
: "S" (sizeof(sa))
: "esp");
sa = 1;
return use_sa(&sa);
}
int main() {
return doit();
}
compiled with 'clang++ -m32 -O3' generates incorrect code that will segfault.
The offending machine code looks something like:
00000010 <doit()>:
10: 55 push %ebp
11: 89 e5 mov %esp,%ebp
13: 56 push %esi
14: 83 e4 f0 and $0xfffffff0,%esp
17: 83 ec 20 sub $0x20,%esp
1a: 89 e6 mov %esp,%esi
1c: be 04 00 00 00 mov $0x4,%esi
21: 90 nop
22: c7 46 10 01 00 00 00 movl $0x1,0x10(%esi)
29: 8d 46 10 lea 0x10(%esi),%eax
2c: 89 04 24 mov %eax,(%esp)
2f: e8 cc ff ff ff call 0
<use_sa(int*)>
34: 8d 65 fc lea -0x4(%ebp),%esp
37: 5e pop %esi
38: 5d pop %ebp
39: c3 ret
3a: 66 0f 1f 44 00 00 nopw 0x0(%eax,%eax,1)
Note the write to %esi @ 1c and then the dereference @ 29.
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