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

[Laszlo Ersek]

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.

Thanks,
Laszlo

> 
> (There is also 'make check-softfloat', listed in 'make check-help')
> 
>>
>>  include/fpu/softfloat.h  |   1 +
>>  target/i386/fpu_helper.c | 426 +++++++++++++++++++--------------------
>>  2 files changed, 214 insertions(+), 213 deletions(-)
>>
>> diff --git a/include/fpu/softfloat.h b/include/fpu/softfloat.h
>> index f1a19df066b7..659218b5c787 100644
>> --- a/include/fpu/softfloat.h
>> +++ b/include/fpu/softfloat.h
>> @@ -822,6 +822,7 @@ static inline bool floatx80_invalid_encoding(floatx80 a)
>>  }
>>  
>>  #define floatx80_zero make_floatx80(0x0000, 0x0000000000000000LL)
>> +#define floatx80_zero_init make_floatx80_init(0x0000, 0x0000000000000000LL)
>>  #define floatx80_one make_floatx80(0x3fff, 0x8000000000000000LL)
>>  #define floatx80_ln2 make_floatx80(0x3ffe, 0xb17217f7d1cf79acLL)
>>  #define floatx80_pi make_floatx80(0x4000, 0xc90fdaa22168c235LL)
>> diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
>> index f5e6c4b88d4e..4ea73874d836 100644
>> --- a/target/i386/fpu_helper.c
>> +++ b/target/i386/fpu_helper.c
>> @@ -868,201 +868,201 @@ struct f2xm1_data {
>>  };
> ...
>