The GAS assembler implicitly converts near->far branches

[palmer-dabbelt]

This wasn't written down anywhere, but I'm pretty sure we've been doing it since the original port and at least GCC depends on it.

Signed-off-by: Palmer Dabbelt palmer@rivosinc.com

[cmuellner]

I would search for that information in the RISC-V Toolchain Conventions, but since that document references the RISC-V Asm Manual in the Assembler behavior section, this PR is fine.

@kito-cheng, any opinion? If not, I'll merge this PR later this week.

[kito-cheng]

Generally LGTM, but I would like to add some word to mention some compiler e.g. LLVM isn't support that...although the patch for that is restart the discussion recently, but so far all clang/llvm release isn't support that feature.

[cmuellner]

Thanks for adding the necessary context!

Here is a summary of the situation:

• GAS does the conversion since day 0
• Upstream LLVM does not do this conversion
• Nobody likes this "magic" but tools depend on it
• Removing the need for this conversion would be much work and break existing code
• Specifying (=requiring) the conversion and implementing it in LLVM would be the easy path
• Having different behavior in GAS and LLVM is what everyone wants to avoid

We can set a deadline until someone can bring up a better solution. But given people repeatedly (every year) stumble into this undocumented and unexpected behavior, we should solve it this time while everyone's attention is raised.

[nick-knight]

Is there overlap between @palmer-dabbelt 's PR and this one I filed a few years ago? #58

[palmer-dabbelt]

Is there overlap between @palmer-dabbelt 's PR and this one I filed a few years ago? #58

Looks like it's doing the same thing, just with different words.

[kito-cheng]

LLVM support this as well on LLVM 16, so let merge!

Ref:
[1] LLVM patech: https://reviews.llvm.org/D108961