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

[Philippe Mathieu-Daudé]

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 :^)

(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 {
>  };
...