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

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Message-ID: <63aec56f-9ade-48d1-854b-bd72f8313a9f@csgroup.eu>
Date: Mon, 27 Jan 2025 13:04:27 +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 12:44, Dmitry V. Levin a écrit :
> On Mon, Jan 27, 2025 at 12:36:53PM +0100, Christophe Leroy wrote:
>> 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().
> 
> Yes, but here similarities end, and differences begin.
> 
>> 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 ?
> 
> Did you mean syscall_set_return_value?  No, it explicitly has two
> arguments, "int error" and "long val", so it can be used to either
> clear or set the error condition as specified by the caller.

Sorry, I mean syscall_get_return_value() here.

static inline long syscall_get_return_value(struct task_struct *task,
					    struct pt_regs *regs)
{
	return regs->gpr[3];
}

Versus

static inline void regs_set_return_value(struct pt_regs *regs, unsigned 
long rc)
{
	regs->gpr[3] = rc;
}

> 
>> By the way, why have two very similar APIs, one in syscall.h one in
>> ptrace.h ?
> 
> I have no polite answer to this, sorry.
> 
>