Date: Mon, 14 Apr 2008 20:18:22 +0400 (MSD) From: Chagin Dmitry <chagin.dmitry@gmail.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-emulation@freebsd.org, Chagin Dmitry <chagin.dmitry@gmail.com> Subject: Re: Call for review && test: linux_kdump-1.6 Message-ID: <20080414194041.Q6842@ora.chd.net> In-Reply-To: <20080414134935.GI18958@deviant.kiev.zoral.com.ua> References: <20080412181712.Y38920@ora.chd.net> <20080412145401.GA4139@freebsd.org> <20080413214624.S7426@ora.chd.net> <20080413183248.GA68642@freebsd.org> <20080413183659.GA18958@deviant.kiev.zoral.com.ua> <20080413231135.K1079@ora.chd.net> <20080413192614.GC18958@deviant.kiev.zoral.com.ua> <20080413234359.H1165@ora.chd.net> <20080414123137.GH18958@deviant.kiev.zoral.com.ua> <20080414134935.GI18958@deviant.kiev.zoral.com.ua>
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On Mon, 14 Apr 2008, Kostik Belousov wrote:
> On Mon, Apr 14, 2008 at 03:31:37PM +0300, Kostik Belousov wrote:
>> On Mon, Apr 14, 2008 at 12:42:29AM +0400, Chagin Dmitry wrote:
>>> On Sun, 13 Apr 2008, Kostik Belousov wrote:
>>>
>>>> On Sun, Apr 13, 2008 at 11:11:55PM +0400, Chagin Dmitry wrote:
>>>>> On Sun, 13 Apr 2008, Kostik Belousov wrote:
>>>>>
>>>>>> On Sun, Apr 13, 2008 at 08:32:48PM +0200, Roman Divacky wrote:
>>>>>>> On Sun, Apr 13, 2008 at 09:58:08PM +0400, Chagin Dmitry wrote:
>>>>>>>> On Sat, 12 Apr 2008, Roman Divacky wrote:
>>>>>>>>
>>>>>>>>>> And question: whether i can add to linuxolator some ktr_struct
>>>>>>>>>> functionality?
>>>>>>>>>
>>>>>>>>> sure... please provide a patch and I'll take care about it.
>>>>>>>>
>>>>>>>> ok, thnx :)
>>>>>>>> what about EJUSTRETURN?
>>>>>>>> i attached simple patch for demo only (not tested).
>>>>>>>
>>>>>>> uh... can you provide diff -u ? I dont understand the diff at all ;)
>>>>>>
>>>>>> Also, please note that the ML software strips your attachments. Either
>>>>>> inline the patch, or use the plain-text content-type for it.
>>>>>>
>>>>>
>>>>> ups... ah google ))
>>>>> i have understood, sorry and thnx.
>>>>> Speech about that in linux_kdump it is impossible to distinguish
>>>>> EJUSTRETURN from a real error. look:
>>>>>
>>>>> --- sys/i386/i386/trap.c.orig 2008-04-13 21:39:18.000000000 +0400
>>>>> +++ sys/i386/i386/trap.c 2008-04-13 22:35:25.000000000 +0400
>>>>> @@ -1091,8 +1091,12 @@
>>>>> td->td_proc->p_pid, td->td_name, code);
>>>>>
>>>>> #ifdef KTRACE
>>>>> - if (KTRPOINT(td, KTR_SYSRET))
>>>>> - ktrsysret(code, error, td->td_retval[0]);
>>>>> + if (KTRPOINT(td, KTR_SYSRET)) {
>>>>> + if (error == EJUSTRETURN)
>>>>> + ktrsysret(code, 0, td->td_retval[0]);
>>>>> + else
>>>>> + ktrsysret(code, error, td->td_retval[0]);
>>>>> + }
>>>>> #endif
>>>>>
>>>>> /*
>>>>> @@ -1104,4 +1108,3 @@
>>>>>
>>>>> PTRACESTOP_SC(p, td, S_PT_SCX);
>>>>> }
>>>>> -
>>>>
>>>> I do not quite understand the intent of this change.
>>>>
>>>> EJUSTRETURN is used for two different purposes in the kernel.
>>>> 1. The sigreturn family of the syscalls use it after the interrupted
>>>> frame is restored to avoid the normal syscall return sequence to modify
>>>> the machine state.
>>>> 2. It is used by the kernel to notify the in-kernel caller code about
>>>> some special condition, that nonetheless shall not be returned to the
>>>> userspace.
>>>>
>>>> Only the first case is applicable to the kdump, and IMHO you actually
>>>> destroy some information, since error == EJUSTRETURN is reported as 0.
>>>>
>>>> Could you, please, provide some more arguments in the support of your
>>>> proposed change ?
>>>>
>>>
>>> Thanks for you informative reply Kostya.
>>> The problem arises only in linux_kdump. Because linux error
>>> codes negative and EJUSTRETURN coincides with ENOENT.
>>> Before a call ktr_sysret we decode return codes of emulators syscalls.
>>
>> Ah, I see. Then, we shall never dump the ERESTART and EJUSTRETURN
>> for the emulated ABIs. At least, this is true for Linux, I am not
>> so sure about iBCS2 and SVR4.
>>
I do not absolutely agree with this statement. If the emulated syscalls
should return native FreeBSD errno, that why to not write them to a
ktrace file without conversion? Current linux_kdump port uses strerror
because expects it. At least, it is convenient :)
Your patch is correct for my version of linux_kdump, but does not solve
a problem with the current port version.
If it's possible, explain please, that is not correct in my last patch?
thnx
>> Could you test the patch below, instead ?
>
>> diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
>> index e7de579..55642d1 100644
>> --- a/sys/i386/i386/trap.c
>> +++ b/sys/i386/i386/trap.c
>
> The patch is obviously wrong, it just prevents the Linux ENOENT to be
> dumped. Please, try this one instead.
>
> diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
> index b6a454d..3b1368a 100644
> --- a/sys/amd64/amd64/trap.c
> +++ b/sys/amd64/amd64/trap.c
> @@ -861,9 +861,18 @@ syscall(struct trapframe *frame)
> frame->tf_rip -= frame->tf_err;
> frame->tf_r10 = frame->tf_rcx;
> td->td_pcb->pcb_flags |= PCB_FULLCTX;
> - break;
> -
> + /* FALLTHROUGH */
> case EJUSTRETURN:
> +#ifdef KTRACE
> + /*
> + * The ABIs that use the negative error codes, like
> + * Linux, would confuse the in-kernel errno values
> + * with proper userspace errno. Clean these values to
> + * avoid a confusion in the kdump.
> + */
> + if (p->p_sysent->sv_errsize)
> + error = 0;
> +#endif
> break;
>
> default:
> diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
> index e7de579..6ec04b0 100644
> --- a/sys/i386/i386/trap.c
> +++ b/sys/i386/i386/trap.c
> @@ -1040,9 +1040,18 @@ syscall(struct trapframe *frame)
> * int 0x80 is 2 bytes. We saved this in tf_err.
> */
> frame->tf_eip -= frame->tf_err;
> - break;
> -
> + /* FALLTHROUGH */
> case EJUSTRETURN:
> +#ifdef KTRACE
> + /*
> + * The ABIs that use the negative error codes, like
> + * Linux, would confuse the in-kernel errno values
> + * with proper userspace errno. Clean these values to
> + * avoid a confusion in the kdump.
> + */
> + if (p->p_sysent->sv_errsize)
> + error = 0;
> +#endif
> break;
>
> default:
>
--
Have fun!
chd
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