tree e2777fa96263e04540cd8a5a7336e7fe832fa0df
parent 7cb90e092f2eee7dde7fd73ea39fb491123554f6
author David Benjamin <davidben@google.com> 1668870955 -0500
committer Boringssl LUCI CQ <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com> 1670535005 +0000

Fully condition all assembly files.

For the C files, rather than force the caller to juggle
crypto_linux_sources, etc., we just wrap the whole file in ifdefs and
ask the callers to link everything together.

Assembly is typically built by a different tool, so we have less room
here. However, there are really only two families of tools we care
about: gas (which runs the C preprocessor) and nasm (which has its own
preprocessor). Callers should be able to limit themselves to
special-casing Windows x86(_64) for NASM and then pass all the remaining
assembly files to their gas-like tool. File-wide ifdefs can take care of
the rest.

We're almost set up to allow this, except the files condition on
architecture, but not OS. Add __ELF__, __APPLE__, and _WIN32 conditions
as appropriate.

One subtlety: the semantics of .note.GNU-stack are that *any* unmarked
object file makes the stack executable. (In current GNU ld. lld doesn't
have this issue, and GNU ld claims they'll remove it in a later
release.) Empirically, this doesn't seem to apply to empty object files
but, to be safe, we should ensure all object files have the marking.

That leads to a second subtlety: on targets where @ is a comment,
@progbits is spelled %progbits, per [0]. If we want all .S files to work
in all targets, that includes these markers. Fortunately, %progbits
appears to work universally (see [1], [2], [3], [4]), so I've just
switched us to that spelling.

I've also tightened up the __arm__ and __aarch64__ checks to __ARMEL__
and __AARCH64EL__. We don't support big-endian Arm (or any other
platform) and, even if we did, the conditions in the assembly files
should match the conditions in the C files that pull them in.

This CL doesn't change our build to take advantage of this (though I'll
give it a go later), just makes it possible for builds to do it.

[0] https://sourceware.org/binutils/docs/as/Section.html
[1] https://patchwork.kernel.org/project/linux-crypto/patch/20170119212805.18049-1-dvlasenk@redhat.com/#20050285
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92820#c11
[3] https://sourceware.org/legacy-ml/gdb-patches/2016-01/msg00319.html
[4] https://github.com/llvm/llvm-project/commit/de990b270d73632a834cb37e6ea50db093321aad

Bug: 542
Change-Id: I0a8ded24423087c0da13bd0335cbd757d4eee65a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55626
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>