linux-kernel - Re: [PATCH] x86/signal: Remove pax argument from restore

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Message-ID: <CAMzpN2gDPej+M=3D_m0-MmtyZ+VYpP=D3GxdP6aEpzH8JeWg9Q@mail.gmail.com>
Date:	Sat, 4 Apr 2015 20:01:14 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/signal: Remove pax argument from restore_sigcontext

On Sat, Apr 4, 2015 at 10:14 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Brian Gerst <brgerst@...il.com> wrote:
>
>> The pax argument is unnecesary.  Instead, store the RAX value directly
>> in regs.
>>
>> Signed-off-by: Brian Gerst <brgerst@...il.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: Andy Lutomirski <luto@...capital.net>
>> Cc: Denys Vlasenko <dvlasenk@...hat.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: x86@...nel.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>  arch/x86/ia32/ia32_signal.c        | 17 ++++++-----------
>>  arch/x86/include/asm/sighandling.h |  4 +---
>>  arch/x86/kernel/signal.c           | 22 ++++++++--------------
>>  3 files changed, 15 insertions(+), 28 deletions(-)
>>
>> diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
>> index 1f5e2b0..c81d35e6 100644
>> --- a/arch/x86/ia32/ia32_signal.c
>> +++ b/arch/x86/ia32/ia32_signal.c
>> @@ -161,8 +161,7 @@ int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
>>  }
>>
>>  static int ia32_restore_sigcontext(struct pt_regs *regs,
>> -                                struct sigcontext_ia32 __user *sc,
>> -                                unsigned int *pax)
>> +                                struct sigcontext_ia32 __user *sc)
>>  {
>>       unsigned int tmpflags, err = 0;
>>       void __user *buf;
>> @@ -184,7 +183,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
>>               RELOAD_SEG(es);
>>
>>               COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx);
>> -             COPY(dx); COPY(cx); COPY(ip);
>> +             COPY(dx); COPY(cx); COPY(ip); COPY(ax);
>>               /* Don't touch extended registers */
>>
>>               COPY_SEG_CPL3(cs);
>> @@ -197,8 +196,6 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
>>
>>               get_user_ex(tmp, &sc->fpstate);
>>               buf = compat_ptr(tmp);
>> -
>> -             get_user_ex(*pax, &sc->ax);
>>       } get_user_catch(err);
>
> Note that arch/x86/kernel/signal.c appears to have a similar pattern -
> and there it could be removed as well?
>
> I'm wondering what the original reason for adding the extra handling
> of regs->ax was. Maybe something changed regs->ax - but I cannot find
> such code path anymore.
>
> It would be nice to try to do a bit of Git archeology to figure out
> the origins of this complication - maybe it's something subtle - or
> it's something that has changed meanwhile.

It goes all the way back to 2.1.106pre1, when restore_sigcontext() was
changed to return an error code instead of EAX directly.

https://git.kernel.org/cgit/linux/kernel/git/history/history.git/diff/arch/i386/kernel/signal.c?id=9a8f8b7ca3f319bd668298d447bdf32730e51174

--
Brian Gerst
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