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


From: Laurent Vivier
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] linux-user: fix signal() syscall on x86_64
Date: Thu, 7 Jul 2016 21:02:51 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1


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



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