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

[Laszlo Ersek]

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.

Laszlo