linux-kernel - Re: nios2: is the ptrace ABI correct?

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Date:	Wed, 25 Feb 2015 15:07:39 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:	Tobias Klauser <tklauser@...tanz.ch>,
	Chung-Ling Tang <cltang@...esourcery.com>,
	Walter Goossens <waltergoossens@...e.nl>,
	Ley Foon Tan <lftan@...era.com>, linux-arch@...r.kernel.org,
	"nios2-dev@...ts.rocketboards.org" <nios2-dev@...ts.rocketboards.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: nios2: is the ptrace ABI correct?

On Wednesday 25 February 2015 08:33:16 Ezequiel Garcia wrote:
> 
> /me is more confused now
> 
> In arch/nios2/include/asm/ucontext.h
> 
> struct ucontext {
>         unsigned long     uc_flags;
>         struct ucontext  *uc_link;
>         stack_t           uc_stack;
>         struct mcontext   uc_mcontext;
>         sigset_t          uc_sigmask;
> };
> 
> And in include/uapi/asm-generic/ucontext.h:
> 
> struct ucontext {
>         unsigned long     uc_flags;
>         struct ucontext  *uc_link;
>         stack_t           uc_stack;
>         struct sigcontext uc_mcontext;
>         sigset_t          uc_sigmask;
> };
> 
> Which one is the one that userspace sees? And why does the kernel has
> two different structures?

Userspace sees the asm-generic header, which I assume is a bug
in this case.

> Given this oddities, I'm wondering how troublesome would be to just
> re-do this and break the ptrace and signal ABI. For instance, just
> pushing pt_regs in PTRACE_GETREGSET would make things much clearer.

Could you change pt_regs to match the layout you have for PTRACE_GETREGSET
instead? It seems much more intuitive.

> I guess Linus would burn me for even suggesting to breaking users... but
> do we have any users at all? This arch has just been mainlined. Altera's
> out-of-tree is already ABI-incompatible with mainline so that's not an
> issue.
> 
> The only one using this ABI is gdb, which is easily fixed.

You can change anything you like as long as nobody complains about
regressions.

	Arnd
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