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Re: [Qemu-devel] [PATCH] linux-user: fix signal() syscall on x86_64


From: Wirth, Allan
Subject: Re: [Qemu-devel] [PATCH] linux-user: fix signal() syscall on x86_64
Date: Thu, 7 Jul 2016 19:04:04 +0000


On 7/7/16, 3:02 PM, "Laurent Vivier" <address@hidden> wrote:

>
>
>Le 07/07/2016 à 20:49, Riku Voipio a écrit :
>> On Sat, Jul 02, 2016 at 09:12:09PM +0100, Peter Maydell wrote:
>>> On 2 July 2016 at 17:41, Laurent Vivier <address@hidden> wrote:
>>>> Sadly, this can't work:
>>>>
>>>> sparc/sparc64/cris use sys_select for NR_select AND NR_newselect.
>>>
>>>> Not sure all is correct, but it's what I've found:
>>>>
>>>>             | __NR_select    | __NR__newselect
>>>> ------------+----------------+-----------------+
>>>> arm         | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> aarch64     | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> alpha       | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> cris        | sys_select     | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> m68k        | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> microblaze  | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> mips        | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> mips64      | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> openrisc    | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> ppc         | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> s390x       | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> sh4         | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> sparc       | sys_select     | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> sparc64     | sys_select     | sys_select      |
>>>> ------------+----------------+-----------------+
>>>> tilegx      | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> unicore32   | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> x86_64      | sys_select     |        -        |
>>>> ------------+----------------+-----------------+
>>>> i386        | sys_old_select | sys_select      |
>>>> ------------+----------------+-----------------+
>>>
>>> Hmm. Looking at current Linux git master, I get
>>> slightly different results. The only architectures which
>>> define __ARCH_WANT_SYS_OLD_SELECT are:
>>>  arm, m68k, mn10300, x86
>>> and no others use sys_old_select.
>>>
>>> So I think we have the following behaviours:
>>>
>>> (1) Define neither NR_select nor NR__newselect
>>>  (and use pselect6 syscall for select):
>>>  aarch64, openrisc, tilegx, unicore32, presumably any future arch
>>>
>>> (2) only define NR__newselect, it is new select:
>>>  mips, mips64, sh, s390
>>>
>>> (3) Only define NR_select, want that to be new select:
>>>  alpha, x86_64, s390x
>>>
>>> (4) NR__newselect is new select, NR_select is old_select:
>>>  i386, m68k, arm if kernel is not CONFIG_AEABI
>>>
>>> (5) NR__newselect is new select, NR_select is defined but
>>>  if called returns ENOSYS:
>>>  microblaze, arm if CONFIG_AEABI, ppc64
>>>
>>> (6) NR__newselect is new select, NR_select is a bonkers custom
>>>  thing that tries to autodetect the calling convention:
>>> http://lxr.free-electrons.com/source/arch/powerpc/kernel/syscalls.c#L86
>>>  ppc32 (but only native 32-bit; 32-bit compat support
>>>  on a ppc64 kernel is category 5, so I vote for ignoring
>>>  this weirdness and calling ppc category 5)
>>>
>>> (7) NR_select and NR__newselect are different numbers
>>>  but both are new select:
>>>  cris, sparc, sparc64
>>>
>>> which is a pretty confusing mess, but I think it equates to:
>>> (0) if defined, NR__newselect is always new select
>>> (1) if NR_select is defined, the choices are:
>>>  (a) NR_select is old_select:
>>>    i386, m68k, arm
>>>  (b) NR_select is defined but should ENOSYS:
>>>    microblaze, ppc
>>>  (c) NR_select defined and is new select:
>>>    everything else (alpha, x86-64, s390x, cris, sparc, sparc64)
>>>
>>> and I think we should handle that by having the code in syscall.c
>>> be something like:
>>>
>>> #ifdef TARGET_NR_select
>>>     case TARGET_NR_select:
>>> #if defined(TARGET_WANT_NI_OLD_SELECT)
>>>         /* some architectures used to have old_select here
>>>          * but now ENOSYS it.
>>>          */
>>>         ret = -TARGET_ENOSYS;
>>>         break;
>>> #elif defined(TARGET_WANT_OLD_SYS_SELECT)
>>>         /* code for old select here; maybe factored out to
>>>          * its own function: ret = do_old_select() ?
>>>          */
>>> #else
>>>         /* select is new style select */
>>>         ret = do_select(...);
>>> #endif
>>> #endif
>> 
>> I agree, this seems to be the best way to fix select properly.
>
>Ok, if no one is already working on that, I'm going to send a patch
>according to Peter's comments.
>
>Laurent

I was hoping to, but I do not think that I will get around to it anytime soon.

-Allan


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