More info: Binary built on different platforms with exact same tools different?

[Rick Mann <rmann@latencyzero.com>]

On Dec 17, 2007, at 4:43 PM, Rick Mann wrote:

> Hi. I've built an xscale-elf toolchain from gcc-4.2.2,  
> binutils-2.17, newlib-1.15.0. I've used the exact same build  
> procedure on both Mac OS X 10.5 (gcc-4.0.1-based) and Cygwin (gcc  
> 3.4-based).
>
> Then I built our code and stripped the resulting binary with objcopy  
> on each platform.
>
> Both binaries seem to run the same.
>
> However, cmp shows many differences between the two resulting  
> binaries. Here are a few:
>
> $ cmp -l ~/h h | head -10
>     77  21  63
>     81  32  74
>     85  27  71
>     97 370 220
>     98 162 163
>    101 134 364
>    105 134 364
>    141   4  15
>    143  55 240
>    144 345 341
>
>
> Are these differences something to worry about?

I've disassembled the .elf files, and here are some of the differences:

Mac OS X:

8000804c <loop>:
8000804c:	eb00a933 	bl	80032520 <_init>
80008050:	eb000c3c 	bl	8000b148 <main>
80008054:	eb00a939 	bl	80032540 <_fini>
80008058:	eaffffe8 	b	80008000 <//.>
8000805c:	e89da800 	ldmia	sp, {fp, sp, pc}
...
80008060 <bss_start>:
80008060:	80047390 	mulhi	r4, r0, r3

80008064 <bss_end>:
80008064:	803a51f4 	ldrhisht	r5, [sl], -r4


Cygwin:

8000804c <loop>:
8000804c:	eb00a911 	bl	80032498 <_init>
80008050:	eb000c1a 	bl	8000b0c0 <main>
80008054:	eb00a917 	bl	800324b8 <_fini>
80008058:	eaffffe8 	b	80008000 <//.>
8000805c:	e89da800 	ldmia	sp, {fp, sp, pc}
...
80008060 <bss_start>:
80008060:	800472f8 	strhid	r7, [r4], -r8

80008064 <bss_end>:
80008064:	803a515c 	eorhis	r5, sl, ip, asr r1


Some functions are placed in different order, too.

I'm trying to ensure that all our developers build identical binaries.

TIA,
-- 
Rick