I. J. Kennedy I. J. Kennedy - 1 month ago 11
Linux Question

Is there a way to get gcc to output raw binary?

Is there a set of command-line options that will convince gcc to produce a flat binary file from a self-contained source file? For example, suppose the contents of foo.c are

static int f(int x)
{
int y = x*x;
return y+2;
}


No external references, nothing to export to the linker. I'd like to get a small file with just the machine instructions for this function, without any other decoration. Sort of like a (DOS) .COM file except 32-bit protected mode.

Answer

Try this out:

$ cc -c test.c
$ objcopy -O binary test.o binfile

You can make sure it's correct with objdump:

$ objdump -d test.o 
test.o:     file format pe-i386


Disassembly of section .text:

00000000 <_f>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 ec 04                sub    $0x4,%esp
   6:   8b 45 08                mov    0x8(%ebp),%eax
   9:   0f af 45 08             imul   0x8(%ebp),%eax
   d:   89 45 fc                mov    %eax,-0x4(%ebp)
  10:   8b 45 fc                mov    -0x4(%ebp),%eax
  13:   83 c0 02                add    $0x2,%eax
  16:   c9                      leave  
  17:   c3                      ret

And compare to the binary file:

$ hexdump -C binfile 
00000000  55 89 e5 83 ec 04 8b 45  08 0f af 45 08 89 45 fc  |U......E...E..E.|
00000010  8b 45 fc 83 c0 02 c9 c3                           |.E......|
00000018
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