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

Dmitry V. Levin
2025-01-27T11:44:40Z

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.

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ldv