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

[Sid Manning]

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"

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>