[PATCH] D18055: ELF: Implement --build-id.

[Rafael Espíndola via llvm-commits]

BTW, have you tried this in combination with the patch for using
posix_memalign? Since this basically reads back the output of the
linker I would be curious if that patch makes any difference is the
results.

>  - Use CRC32 instead of MD5. Non-secure hash should be much faster.

That is a bit too weak I think, but we can block this on getting a
better MD5 or use another strong but fast hash.

>  - Make clang to calculate a secure hash for each section.
>    This is basically moving the workload from the linker to the compiler,
>    but we can use the hash for ICF in the linker,
>    so it might be a overall win.

Seems like something we should do in the future, but should not depend
on it. That is, having the hash available speeds up build-id, but
build-id should work without it.

>  - Compute a build-id from input files' timestamps. This makes builds
>    non-reproducible if you touch a file, so I don't think we want this.

Not this. O use of build-id is for checking for reproducible builds I think.

>  - Build-id is not needed for program execution in general.
>    So we may be able to let the linker exit as soon as it's done with linking,
>    and backfill the hash value in a background process which is kicked in
>    by the linker. (It's probably unrealistic plan, though.)

A bit dangerous I would say.


Cheers,
Rafael