[LLVMdev] gcc bug?..segfault problem with getElfArchType.

[Michael Spencer]

On Sat, Jun 30, 2012 at 7:58 AM, Sid Manning <sidneym at codeaurora.org> wrote:
>
> I've been debugging a segfault issue with the elfreader and I would like to
> point out something that I have noticed.
>
> ELF.h declares an inline function, getElfArchType (MemoryBuffer *Object).
>  When this function is called from ObjectFile::createELFObjectFile the
> pointer to Object was getting corrupted.  The only thing that distinguished
> this pointer was that it was declared as a unique_ptr.  The flow from when
> it was created to getElfArchType is pretty direct.
>
> The segfault only happens only at optimization level -O0.
> The segfault doesn't happen if getElfArchType is declared as, "static
> inline"

Is this occurring with ELF.h in lld? If so this sounds like your
compiling llvm and lld with different standard libraries and because
-O0 doesn't inline, the linkonce linkage is picking the wrong one.

- Michael Spencer

> FWIW I'm compiling on x86_64/gcc-4.7.1.
>
>
> This is the assembly, (widen your email window!)
>
> Broken: Call side
> ObjectFile *ObjectFile::createELFObjectFile(MemoryBuffer *Object) {
> 0x00000000004cc864
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE>:
> push   %rbp
> 0x00000000004cc865
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+1>:
>  mov    %rsp,%rbp
> 0x00000000004cc868
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+4>:
>  push   %rbx
> 0x00000000004cc869
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+5>:
>  sub    $0x38,%rsp
> 0x00000000004cc86d
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+9>:
>  mov    %rdi,-0x38(%rbp)
>  std::pair<unsigned char, unsigned char> Ident = getElfArchType(Object);
> 0x00000000004cc871
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+13>:
>  mov    -0x38(%rbp),%rax
> 0x00000000004cc875
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+17>:
>  mov    %rax,%rdi
> 0x00000000004cc878
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+20>:
>  callq  0x4a51c5 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE>
>
> Callee side: The address of *Object is at -0x18(%rbp) not -0x20(%rbp):
>
> 0x00000000004a51c5 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE>:
>  push   %rbp
> 0x00000000004a51c6 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+1>:
>  mov    %rsp,%rbp
> 0x00000000004a51c9 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+4>:
>  sub    $0x20,%rsp
> 0x00000000004a51cd <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+8>:
>  mov %rdi,-0x18(%rbp)
> 0x00000000004a51d1 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+12>:
> mov %rsi,-0x20(%rbp)
> 0x00000000004a51d5 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+16>:
> mov -0x20(%rbp),%rax
> 0x00000000004a51d9 <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+20>:
> mov    %rax,%rdi
> 0x00000000004a51dc <_ZN4llvm6object14getElfArchTypeEPNS_12MemoryBufferE+23>:
> callq 0x4a4a74 <_ZNK4llvm12MemoryBuffer13getBufferSizeEv>
>
>
>
>
> Working version call side, getElfArchType is "static inline"
>
> ObjectFile *ObjectFile::createELFObjectFile(MemoryBuffer *Object) {
> 0x00000000004cc8da
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE>:
> push   %rbp
> 0x00000000004cc8db
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+1>:
>  mov    %rsp,%rbp
> 0x00000000004cc8de
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+4>:
>  push   %rbx
> 0x00000000004cc8df
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+5>:
>  sub    $0x38,%rsp
> 0x00000000004cc8e3
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+9>:
>  mov    %rdi,-0x38(%rbp)
>  std::pair<unsigned char, unsigned char> Ident = getElfArchType(Object);
> 0x00000000004cc8e7
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+13>:
>  mov    -0x38(%rbp),%rax
> 0x00000000004cc8eb
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+17>:
>  mov    %rax,%rdi
> 0x00000000004cc8ee
> <_ZN4llvm6object10ObjectFile19createELFObjectFileEPNS_12MemoryBufferE+20>:
>  callq  0x4cc868 <getElfArchType>
>
> Callee side gets the correct address:
> 0x00000000004cc868 <getElfArchType>:    push   %rbp
> 0x00000000004cc869 <getElfArchType+1>:  mov    %rsp,%rbp
> 0x00000000004cc86c <getElfArchType+4>:  push   %rbx
> 0x00000000004cc86d <getElfArchType+5>:  sub    $0x18,%rsp
> 0x00000000004cc871 <getElfArchType+9>:  mov    %rdi,-0x18(%rbp)
> 0x00000000004cc875 <getElfArchType+13>: mov    -0x18(%rbp),%rax
> 0x00000000004cc879 <getElfArchType+17>: mov    %rax,%rdi
> 0x00000000004cc87c <getElfArchType+20>: callq  0x4a4b06
> <_ZNK4llvm12MemoryBuffer13getBufferSizeEv>
>