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

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Message-ID: <20250127114439.GC29522@strace.io>
Date: Mon, 27 Jan 2025 13:44:39 +0200
From: "Dmitry V. Levin" <ldv@...ace.io>
To: Christophe Leroy <christophe.leroy@...roup.eu>
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()

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.

> 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.


-- 
ldv