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From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date: Tue, 27 Feb 2024 15:47:29 +0100
Message-ID: <CANiq72=69uBBhKMrw5P8K6eDHPiwAw_Oj8g1aYcywEYhhUG8OA@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] scripts: generate_rust_target: enable building on RISC-V
To: Conor Dooley <conor.dooley@microchip.com>
Cc: Conor Dooley <conor@kernel.org>, linux-riscv@lists.infradead.org, 
	Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, 
	Wedson Almeida Filho <wedsonaf@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, 
	=?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, 
	Jonathan Corbet <corbet@lwn.net>, Paul Walmsley <paul.walmsley@sifive.com>, 
	Palmer Dabbelt <palmer@dabbelt.com>, Nathan Chancellor <nathan@kernel.org>, 
	Nick Desaulniers <ndesaulniers@google.com>, Tom Rix <trix@redhat.com>, 
	rust-for-linux@vger.kernel.org, linux-doc@vger.kernel.org, 
	linux-kernel@vger.kernel.org, llvm@lists.linux.dev
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On Tue, Feb 27, 2024 at 1:37=E2=80=AFPM Conor Dooley <conor.dooley@microchi=
p.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=3D-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