linux-kernel - Re: [PATCH v2] RISC-V: vDSO: Correct inline assembly constraints in the getrandom syscall wrapper

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Message-Id: 
 <174975903199.88969.16808687093175866673.git-patchwork-notify@kernel.org>
Date: Thu, 12 Jun 2025 20:10:31 +0000
From: patchwork-bot+linux-riscv@...nel.org
To: Xi Ruoyao <xry111@...111.site>
Cc: linux-riscv@...ts.infradead.org, alex@...ti.fr,
 thomas.weissschuh@...utronix.de, nathan@...nel.org, Jason@...c4.com,
 paul.walmsley@...ive.com, palmer@...belt.com, guoren@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] RISC-V: vDSO: Correct inline assembly constraints in
 the
 getrandom syscall wrapper

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <palmer@...belt.com>:

On Fri,  6 Jun 2025 17:24:44 +0800 you wrote:
> As recently pointed out by Thomas, if a register is forced for two
> different register variables, among them one is used as "+" (both input
> and output) and another is only used as input, Clang would treat the
> conflicting input parameters as undefined behaviour and optimize away
> the argument assignment.
> 
> Per an example in the GCC documentation, for this purpose we can use "="
> (only output) for the output, and "0" for the input for that we must
> reuse the same register as the output.  And GCC developers have
> confirmed using a simple "r" (that we use for most vDSO implementations)
> instead of "0" is also fine.
> 
> [...]

Here is the summary with links:
  - [v2] RISC-V: vDSO: Correct inline assembly constraints in the getrandom syscall wrapper
    https://git.kernel.org/riscv/c/2b9518684f85

You are awesome, thank you!
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