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

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Message-ID: <7e7c7659-5cf7-42e9-81d6-b91963d8c892@csgroup.eu>
Date: Mon, 27 Jan 2025 12:36:53 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Dmitry V. Levin" <ldv@...ace.io>
Cc: Alexey Gladkov <legion@...nel.org>, 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>, 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()

Le 27/01/2025 à 12:20, Dmitry V. Levin a écrit :
> On Thu, Jan 23, 2025 at 11:07:21PM +0100, Christophe Leroy wrote:
> [...]
>> To add a bit more to the confusion,
> 
> Looks like there is no end to it:
> 
> static inline long regs_return_value(struct pt_regs *regs)
> {
>          if (trap_is_scv(regs))
>                  return regs->gpr[3];
> 
>          if (is_syscall_success(regs))
>                  return regs->gpr[3];
>          else
>                  return -regs->gpr[3];
> }
> 
> static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
> {
>          regs->gpr[3] = rc;
> }
> 
> This doesn't look consistent, does it?
> 
> 

That regs_set_return_value() looks pretty similar to 
syscall_get_return_value().

regs_set_return_value() documentation in asm-generic/syscall.h 
explicitely says: This value is meaningless if syscall_get_error() 
returned nonzero

Is it the same with regs_set_return_value(), only meaningfull where 
there is no error ?

By the way, why have two very similar APIs, one in syscall.h one in 
ptrace.h ?