linux-kernel - Re: [PATCH v2 2/3] scripts: generate_rust

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Date: Tue, 27 Feb 2024 15:47:29 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: Conor Dooley <conor@...nel.org>, linux-riscv@...ts.infradead.org, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Jonathan Corbet <corbet@....net>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, 
	rust-for-linux@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/3] scripts: generate_rust_target: enable building on RISC-V

On Tue, Feb 27, 2024 at 1:37 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> Looking closer at those targets, all of them enable compressed
> instructors, but we support hardware that does not support them.
> I think that means we are stuck with the custom targets.

Did you try `-Ctarget-feature=-c`? i.e. as far as I know, you can
disable target features even if they are enabled from the built-in.

It seems to work from a quick try (in userspace), e.g.

0000000000000000 <f>:
       0: 9b 05 05 00      sext.w    a1, a0
       4: 13 05 a0 02      li    a0, 0x2a
       8: 63 84 05 00      beqz    a1, 0x10 <f+0x10>
       c: 13 05 b0 07      li    a0, 0x7b
      10: 67 80 00 00      ret

vs.

0000000000000000 <f>:
       0: 9b 05 05 00      sext.w    a1, a0
       4: 13 05 a0 02      li    a0, 0x2a
       8: 99 c1            beqz    a1, 0xe <f+0xe>
       a: 13 05 b0 07      li    a0, 0x7b
       e: 82 80            ret

Cheers,
Miguel