[Tinycc-devel] strange behavior when linking with gcc compiled object file

[Jin Qian]

I am trying to use tcc (ver 0.9.26) to link an object file that's compiled with gcc,  it has strange behavior. The detail is in 

strange behavior when trying to compile a source with tcc against gcc generated .o file

If I compile that file te1.c (shown in the following) with tcc instead and do the linking with tcc, then everything works fine.

The difference I saw is,   when tcc compiles the function call (printf1), it produced "lea    -0x4(%rip),%rcx",  but gcc produced "lea    0(%rip),%rcx"

I even did the experiment by modifying the few bytes of machine code in gcc compiled object file just to make it look like tcc compiled, then linking with tcc produced a good exe.  

Any ideas why tcc does this, why is the "-4" offset in lea instruction? 

Thanks

Jin

==============te1.c======================

#include <stdio.h>

extern void printf1(char *p);

void dummy () {

printf1("1234567in dummy!!!\n");

}

0000000000000000 <dummy>:

   0:   55                      push   %rbp

   1:   48 89 e5                mov    %rsp,%rbp

   4:   48 81 ec 20 00 00 00    sub    $0x20,%rsp

   b:   48 8d 0d fc ff ff ff    lea    -0x4(%rip),%rcx        # e <dummy+0xe>

  12:   e8 fc ff ff ff          callq  13 <dummy+0x13>

  17:   c9                      leaveq

  18:   c3                      retq

  19:   00 00                   add    %al,(%rax)

  1b:   00 01                   add    %al,(%rcx)

  1d:   04 02                   add    $0x2,%al

  1f:   05 04 03 01 50          add    $0x50010304,%eax