Re: [Qemu-trivial] [PATCH v2] libvixl: a64: Skip "-Wunused-variable" for gcc 5.0.0 or higher

[Peter Maydell]

On 11 October 2014 15:13, Chen Gang <address@hidden> wrote:

MJT: please don't put this in -trivial, it will clash with
the update to libvixl 1.6 currently on the list.


> On 10/11/14 22:07, Chen Gang wrote:
>> 'instructions-a64.h' has unused variables for qemu which can be found by
>> gcc 5.0.0 or higher. and qemu needs "-Werror", and cause building break.
>> But they may be used by another projects (not qemu).
>>
>> So for gcc 5.0.0 or higher, need still keep them, but ignore diagnostic
>> (still print warning, but not break building). The related warnings:
>>
>>     CXX   disas/arm-a64.o
>>   In file included from /upstream/qemu/disas/libvixl/a64/disasm-a64.h:32:0,
>>                    from disas/arm-a64.cc:20:
>>   disas/libvixl/a64/instructions-a64.h:98:13: error: 
>> 'vixl::kFP32PositiveInfinity' defined but not used [-Werror=unused-variable]
>>    const float kFP32PositiveInfinity = rawbits_to_float(0x7f800000);
>>                ^
>>   disas/libvixl/a64/instructions-a64.h:99:13: error: 
>> 'vixl::kFP32NegativeInfinity' defined but not used [-Werror=unused-variable]

So, several questions here:

(1) Does anybody know how the header in question should be
providing constant floats and doubles to its users in a way
that doesn't cause gcc to complain? If so, I can pass the
answer along so at least the next version of the library
is OK...

(2) Bonus question, anybody know why gcc is perfectly happy
with the unused integer constants in the .h file but doesn't
like the float and doubles?

(3) Does gcc 5 emit these warnings for all the .cc files
that pull in this header, or only for the arm-a64.cc one?

Some other approaches to this that would confine the
fix to the makefiles rather than requiring us to modify
the vixl source itself:
 a) add a -Wno- option for the affected .o files
 b) use -isystem rather than -I to include the libvixl
    directory on the include path

(a)'s probably better I guess.

thanks
-- PMM