linux-kernel - Re: [PATCH v2 1/7] powerpc: properly negate error in syscall_set_return

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Message-ID: <Z4Zf4MppsrpoPiC1@example.org>
Date: Tue, 14 Jan 2025 14:00:16 +0100
From: Alexey Gladkov <legion@...nel.org>
To: "Dmitry V. Levin" <ldv@...ace.io>
Cc: Oleg Nesterov <oleg@...hat.com>, Michael Ellerman <mpe@...erman.id.au>,
	Eugene Syromyatnikov <evgsyr@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Renzo Davoli <renzo@...unibo.it>,
	Davide Berardi <berardi.dav@...il.com>,
	strace-devel@...ts.strace.io,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] powerpc: properly negate error in
 syscall_set_return_value()

On Mon, Jan 13, 2025 at 07:10:54PM +0200, Dmitry V. Levin wrote:
> Bring syscall_set_return_value() in sync with syscall_get_error(),
> and let upcoming ptrace/set_syscall_info selftest pass on powerpc.
> 
> This reverts commit 1b1a3702a65c ("powerpc: Don't negate error in
> syscall_set_return_value()").
> 
> Signed-off-by: Dmitry V. Levin <ldv@...ace.io>
> ---
>  arch/powerpc/include/asm/syscall.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index 3dd36c5e334a..422d7735ace6 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -82,7 +82,11 @@ static inline void syscall_set_return_value(struct task_struct *task,
>  		 */
>  		if (error) {
>  			regs->ccr |= 0x10000000L;
> -			regs->gpr[3] = error;
> +			/*
> +			 * In case of an error regs->gpr[3] contains
> +			 * a positive ERRORCODE.
> +			 */
> +			regs->gpr[3] = -error;

After this change the syscall_get_error() will return positive value if
the system call failed. Since syscall_get_error() still believes
regs->gpr[3] is still positive in case !trap_is_scv().

Or am I missing something?

It looks like the selftest you mentioned in the commit message doesn't
check the !trap_is_scv() branch.

>  		} else {
>  			regs->ccr &= ~0x10000000L;
>  			regs->gpr[3] = val;
> -- 
> ldv

-- 
Rgrds, legion