GCC 4.3/4.4 vs MSC 6 on i386 optimization for size fail

I am not sure what am I doing wrong, but I've tried reading manuals about calling conventions of GCC and found nothing useful there. My current problem is GCC generates excessively LARGE code for a very simple operation, like shown below.

main.c:

#ifdef __GNUC__
    // defines for GCC
    typedef void (* push1)(unsigned long);
    #define PUSH1(P,A0)((push1)P)((unsigned long)A0)
#else
    // defines for MSC
    typedef void (__stdcall * push1)(unsigned long);
    #define PUSH1(P,A0)((push1)P)((unsigned long)A0)
#endif

int main() {
    // pointer to nasm-linked exit syscall "function".
    // will not work for win32 target, provided as an example.
    PUSH1(0x08048200,0x7F);
}

Now, let's build and dump it with gcc: gcc -c main.c -Os;objdump -d main.o:

main.o:     file format elf32-i386

Disassembly of section .text:

00000000 <.text>:
   0:   8d 4c 24 04             lea    0x4(%esp),%ecx
   4:   83 e4 f0                and    $0xfffffff0,%esp
   7:   ff 71 fc                pushl  -0x4(%ecx)
   a:   b8 00 82 04 08          mov    $0x8048200,%eax
   f:   55                      push   %ebp
  10:   89 e5                   mov    %esp,%ebp
  12:   51                      push   %ecx
  13:   83 ec 10                sub    $0x10,%esp
  16:   6a 7f                   push   $0x7f
  18:   ff d0                   call   *%eax
  1a:   8b 4d fc                mov    -0x4(%ebp),%ecx
  1d:   83 c4 0c                add    $0xc,%esp
  20:   c9                      leave  
  21:   8d 61 fc                lea    -0x4(%ecx),%esp
  24:   c3                      ret

That's the minimum size code I am able to get... If I don't specify -O* or specify other values, it will be 0x29 + bytes long.

Now, let's build it with ms c compiler v 6 (yea, one of year 98 iirc): wine /mnt/ssd/msc/6/cl /c /TC main.c;wine /mnt/ssd/msc/6/dumpbin /disasm main.obj:

Dump of file main.obj

File Type: COFF OBJECT

_main:
  00000000: 55                 push        ebp
  00000001: 8B EC              mov         ebp,esp
  00000003: 6A 7F              push        7Fh
  0000开发者_Python百科0005: B8 00 82 04 08     mov         eax,8048200h
  0000000A: FF D0              call        eax
  0000000C: 5D                 pop         ebp
  0000000D: C3                 ret

How do I make GCC generate the similar by size code? any hints, tips? Don't you agree resulting code should be small as that? Why does GCC append so much useless code? I thought it'd be smarter than such old stuff like msc6 when optimizing for size. What am I missing here?

main() is special here: gcc is doing some extra work to make the stack 16-byte aligned at the entry point of the program. So the size of the result aren't directly comparable... try renaming main() to f() and you'll see gcc generates drastically different code.

(The MSVC-compiled code doesn't need to care about alignment because Windows has different rules for stack alignment.)

This is the best reference I can get. I'm on Windows now and too lazy to login to my Linux to test. Here (MinGW GCC 4.5.2), the code is smaller than yours. One difference is the calling convention, stdcall of course has a few bytes advantage over cdecl (default on GCC if not specified or with -O1 and I guess with -Os, too) to clean up the stack.

Here's the way I compile and the result (source code is purely copy pasted from your post)

gcc -S test.c:

_main:
    pushl   %ebp     #
    movl    %esp, %ebp   #,
    andl    $-16, %esp   #,
    subl    $16, %esp    #,
    call    ___main  #
    movl    $127, (%esp)     #,
    movl    $134513152, %eax     #, tmp59
    call    *%eax    # tmp59
    leave
    ret

gcc -c -o test.o test.c && objdump -d test.o:

test.o:     file format pe-i386


Disassembly of section .text:

00000000 <_main>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 e4 f0                and    $0xfffffff0,%esp
   6:   83 ec 10                sub    $0x10,%esp
   9:   e8 00 00 00 00          call   e <_main+0xe>
   e:   c7 04 24 7f 00 00 00    movl   $0x7f,(%esp)
  15:   b8 00 82 04 08          mov    $0x8048200,%eax
  1a:   ff d0                   call   *%eax
  1c:   c9                      leave
  1d:   c3                      ret
  1e:   90                      nop
  1f:   90                      nop