Re: [PATCH v2 1/7] powerpc: properly negate error in syscall_set_return_value()

[Christophe Leroy]

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.