UNIX for Advanced & Expert Users

I have a problem.

How can I be sure that the binary currently in production is the binary originally produced by the compiler? I ask because recompiling the sources (ALL sources + stripping away the metadata: strip ...) does not give the same result.

I am pretty sure that I wasn't hacked!

Your comments to how this can happen and how to ensure a reproducible binary are highly appreciated.

Thanks

Frank

Some compilers timestamp their output. Ditto some linkers. Immediately after you get an executable file from your compiler, use cksum to get a crc. Record the crc and file length of the executable. Then you can compare the file's current crc and length to what you recorded.

Yes compilers do that, but you get rid of the metadata by using strip.

I have never heard of elf descriptors being called "metadata", but if you think that stuff goes away, how would a kernel know, as one example, where the text segment ends and the data segment begins? And what does this have to do with the price of beans in China on Tuesday? When I look at my strip man page, I see "strip removes the symbol table and line number information from object files". I don't see anything there about removing timestamps. Nothing about removing "metadata" either. Did I miss something?

As Perderabo says - ld can add information to an output executable file. For starters, try ident or what on the executable.

nm will list symbols in the executable file - if it has not been stripped. By the way, strip is not the default behavior for cc myfile.c -o myfile --

cc -s -o myfile myfile.c does strip the image file, as does strip <filename>

Could it be that the compiler and/or linker uses streaming and so produces a different order of objects in the executable, which of course would then mean that the same source code could potentially produce different executables.

Regardless of the wording of "unnecessary" information, would there be other good reasons why sources a, b, c, d does not always produce the byte by byte same executable?