Re: [PATCH V4 23/23] crypto: hisilicon/qm: Workaround to enable build with RISC-V clang

[Conor Dooley <conor@kernel.org>]

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Hey Sunil,

This one made me scratch my head for a bit..

On Tue, Apr 04, 2023 at 11:50:37PM +0530, Sunil V L wrote:
> With CONFIG_ACPI enabled for RISC-V, this driver gets enabled in
> allmodconfig build. The gcc tool chain builds this driver removing the
> inline arm64 assembly code. However, clang for RISC-V tries to build
> the arm64 assembly and below error is seen.

There's actually nothing RISC-V specific about that behaviour, that's
just how clang works. Quoting Nathan:
"Clang performs semantic analysis (i.e., validates assembly) before
dead code elimination, so IS_ENABLED() is not sufficient for avoiding
that error."

> drivers/crypto/hisilicon/qm.c:627:10: error: invalid output constraint '+Q' in asm
>                        "+Q" (*((char __iomem *)fun_base))
>                        ^
> It appears that RISC-V clang is not smart enough to detect
> IS_ENABLED(CONFIG_ARM64) and remove the dead code.

So I think this statement is just not true, it can remove dead code, but
only after it has done the semantic analysis.

The reason that this has not been seen before, again quoting Nathan, is:
"arm64 and x86_64 both support the Q constraint, we cannot build
LoongArch yet (although it does not have support for Q either so same
boat as RISC-V), and ia64 is dead/unsupported in LLVM. Those are the
only architectures that support ACPI, so I guess that explains why we
have seen no issues aside from RISC-V so far."

> As a workaround, move this check to preprocessing stage which works
> with the RISC-V clang tool chain.

I don't think there's much else you can do!
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Perhaps it is also worth adding:
Link: https://github.com/ClangBuiltLinux/linux/issues/999

Cheers,
Conor.

> Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> ---
>  drivers/crypto/hisilicon/qm.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/crypto/hisilicon/qm.c b/drivers/crypto/hisilicon/qm.c
> index e4c84433a88a..a5f521529ab2 100644
> --- a/drivers/crypto/hisilicon/qm.c
> +++ b/drivers/crypto/hisilicon/qm.c
> @@ -611,13 +611,9 @@ EXPORT_SYMBOL_GPL(hisi_qm_wait_mb_ready);
>  static void qm_mb_write(struct hisi_qm *qm, const void *src)
>  {
>  	void __iomem *fun_base = qm->io_base + QM_MB_CMD_SEND_BASE;
> -	unsigned long tmp0 = 0, tmp1 = 0;
>  
> -	if (!IS_ENABLED(CONFIG_ARM64)) {
> -		memcpy_toio(fun_base, src, 16);
> -		dma_wmb();
> -		return;
> -	}
> +#if IS_ENABLED(CONFIG_ARM64)
> +	unsigned long tmp0 = 0, tmp1 = 0;
>  
>  	asm volatile("ldp %0, %1, %3\n"
>  		     "stp %0, %1, %2\n"
> @@ -627,6 +623,11 @@ static void qm_mb_write(struct hisi_qm *qm, const void *src)
>  		       "+Q" (*((char __iomem *)fun_base))
>  		     : "Q" (*((char *)src))
>  		     : "memory");
> +#else
> +	memcpy_toio(fun_base, src, 16);
> +	dma_wmb();
> +#endif
> +
>  }
>  
>  static int qm_mb_nolock(struct hisi_qm *qm, struct qm_mailbox *mailbox)
> -- 
> 2.34.1
> 
> 
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