linux-kernel - Re: [PATCH] Fix get ERESTARTSYS with m32 in x86

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Message-ID: <53613793.6070600@redhat.com>
Date:	Wed, 30 Apr 2014 18:49:07 +0100
From:	Pedro Alves <palves@...hat.com>
To:	Mark Kettenis <mark.kettenis@...all.nl>
CC:	hpa@...or.com, pinskia@...il.com, teawater@...il.com,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	eparis@...hat.com, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, gdb@...rceware.org
Subject: Re: [PATCH] Fix get ERESTARTSYS with m32 in x86_64 when debug by
 GDB

On 04/30/2014 02:35 PM, Mark Kettenis wrote:
>> Date: Tue, 29 Apr 2014 22:10:15 -0700
>> From: "H. Peter Anvin" <hpa@...or.com>
>>
>> On 04/29/2014 10:08 PM, Andrew Pinski wrote:
>>>
>>> restoring the values is hard since even the ptrace interface does not
>>> allow for that.
>>>
>>
>> So that begs the ultimate question, which is: given the fact that there
>> is *state missing* from the state vector (this is the core of the
>> problem), is there a way we can add that state so that gdb will be able
>> to save and restore it?
> 
> Carrying around additional state in GDB is complicated; I'd rather
> avoid it.

Agreed very much.

> arch/x86/kernel/ptrace.c:putreg32() has this bit of code:
> 
>         case offsetof(struct user32, regs.orig_eax):
>                 /*
>                  * A 32-bit debugger setting orig_eax means to restore
>                  * the state of the task restarting a 32-bit syscall.
>                  * Make sure we interpret the -ERESTART* codes correctly
>                  * in case the task is not actually still sitting at the
>                  * exit from a 32-bit syscall with TS_COMPAT still set.
>                  */
>                 regs->orig_ax = value;
>                 if (syscall_get_nr(child, regs) >= 0)
>                         task_thread_info(child)->status |= TS_COMPAT;
>                 break;
> 
> which gets used for 32-bit compat ptrace(2).  Perhaps the same logic
> should be added to putreg() if the child is a 32-bit process?

Sounds like the right fix to me.

-- 
Pedro Alves

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