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

["Alex Bennée" <alex.bennee@linaro.org>]

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.

>
>> 
>> Laszlo
>> 


-- 
Alex Bennée