Re: [PATCH] target/i386: floatx80: avoid compound literals in static initializers

[Laszlo Ersek <lersek@redhat.com>]

On 07/21/20 18:02, Alex Bennée wrote:
> 
> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
> 
>> On 7/17/20 6:46 PM, Laszlo Ersek wrote:
>>> On 07/17/20 11:26, Laszlo Ersek wrote:
>>>> On 07/16/20 17:09, Philippe Mathieu-Daudé wrote:
>>>>> On 7/16/20 4:42 PM, Laszlo Ersek wrote:
>>>>>> Quoting ISO C99 6.7.8p4, "All the expressions in an initializer for an
>>>>>> object that has static storage duration shall be constant expressions or
>>>>>> string literals".
>>>>>>
>>>>>> The compound literal produced by the make_floatx80() macro is not such a
>>>>>> constant expression, per 6.6p7-9. (An implementation may accept it,
>>>>>> according to 6.6p10, but is not required to.)
>>>>>>
>>>>>> Therefore using "floatx80_zero" and make_floatx80() for initializing
>>>>>> "f2xm1_table" and "fpatan_table" is not portable. And gcc-4.8 in RHEL-7.6
>>>>>> actually chokes on them:
>>>>>>
>>>>>>> target/i386/fpu_helper.c:871:5: error: initializer element is not constant
>>>>>>>      { make_floatx80(0xbfff, 0x8000000000000000ULL),
>>>>>>>      ^
>>>>>
>>>>> This reminds me of:
>>>>>
>>>>> commit 6fa9ba09dbf4eb8b52bcb47d6820957f1b77ee0b
>>>>> Author: Kamil Rytarowski <n54@gmx.com>
>>>>> Date:   Mon Sep 4 23:23:06 2017 +0200
>>>>>
>>>>>     target/m68k: Switch fpu_rom from make_floatx80() to make_floatx80_init()
>>>>>
>>>>>     GCC 4.7.2 on SunOS reports that the values assigned to array members
>>>>> are not
>>>>>     real constants:
>>>>>
>>>>>     target/m68k/fpu_helper.c:32:5: error: initializer element is not
>>>>> constant
>>>>>     target/m68k/fpu_helper.c:32:5: error: (near initialization for
>>>>> 'fpu_rom[0]')
>>>>>     rules.mak:66: recipe for target 'target/m68k/fpu_helper.o' failed
>>>>>
>>>>>     Convert the array to make_floatx80_init() to fix it.
>>>>>     Replace floatx80_pi-like constants with make_floatx80_init() as they are
>>>>>     defined as make_floatx80().
>>>>>
>>>>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>>
>>>>>>
>>>>>> We've had the make_floatx80_init() macro for this purpose since commit
>>>>>> 3bf7e40ab914 ("softfloat: fix for C99", 2012-03-17), so let's use that
>>>>>> macro again.
>>>>>>
>>>>>> Fixes: eca30647fc07
>>>>>> Fixes: ff57bb7b6326
>>>>>> Link: https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg06566.html
>>>>>> Link: https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg04714.html
>>>>>> Cc: Alex Bennée <alex.bennee@linaro.org>
>>>>>> Cc: Aurelien Jarno <aurelien@aurel32.net>
>>>>>> Cc: Eduardo Habkost <ehabkost@redhat.com>
>>>>>> Cc: Joseph Myers <joseph@codesourcery.com>
>>>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>>>> Cc: Peter Maydell <peter.maydell@linaro.org>
>>>>>> Cc: Richard Henderson <rth@twiddle.net>
>>>>>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>>>>>> ---
>>>>>>
>>>>>> Notes:
>>>>>>     I can see that there are test cases under "tests/tcg/i386", but I don't
>>>>>>     know how to run them.
>>>>>
>>>>> Yeah it is not easy to figure...
>>>>>
>>>>> Try 'make run-tcg-tests-i386-softmmu'
>>>>> but you need docker :^)
>>>>
>>>> That worked, thanks! Even without Docker: I just had to add
>>>>
>>>>   --cross-cc-i386=gcc
>>>>
>>>> to my ./configure flags.
>>>>
>>>
>>> Also -- I meant to, but I forgot to put "for-5.1" in the subject prefix;
>>> sorry about that.
>>
>> Alex, as Paolo is not available, can this go via your tree?
> 
> Ok queued to for-5.1/fixes-for-rc1-v2, thanks.

Many thanks!
Laszlo