[gdb/build] Fix C inclusion of nat/x86-cpuid.h

  When running test-case gdb.arch/i386-avx512.exp, I run into:
...
 gdb compile failed, In file included from gdb.arch/i386-avx512.c:20:0:
 src/gdb/nat/x86-cpuid.h: In function 'x86_cpuid_count':
 src/gdb/nat/x86-cpuid.h:63:16: error: \
   'nullptr' undeclared (first use in this function)
    if (__eax == nullptr)
                 ^~~~~~~
 src/gdb/nat/x86-cpuid.h:63:16: note: each \
   undeclared identifier is reported only once for each function it appears in

                  === gdb Summary ===

 # of untested testcases         1
...

This is due to commit e85aad4ae76 ("nat/x86-cpuid.h: Add x86_cpuid_count
wrapper around __get_cpuid_count"), which introduced the nullptr check.

The header file gdb/nat/x86-cpuid.h is a file that is included in the build
and compiled as a C++ file, but also in the testsuite and compiled as a C
file.

Fix this by replacing nullptr with (void *)0.

Tested on x86_64-linux.
---
 gdb/nat/x86-cpuid.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)


base-commit: 8468e03688622f265529699e2efd355a4c122cc6
  

On 8/29/23 8:38 AM, Tom de Vries via Gdb-patches wrote:
> When running test-case gdb.arch/i386-avx512.exp, I run into:
> ...
>   gdb compile failed, In file included from gdb.arch/i386-avx512.c:20:0:
>   src/gdb/nat/x86-cpuid.h: In function 'x86_cpuid_count':
>   src/gdb/nat/x86-cpuid.h:63:16: error: \
>     'nullptr' undeclared (first use in this function)
>      if (__eax == nullptr)
>                   ^~~~~~~
>   src/gdb/nat/x86-cpuid.h:63:16: note: each \
>     undeclared identifier is reported only once for each function it appears in
> 
>                    === gdb Summary ===
> 
>   # of untested testcases         1
> ...
> 
> This is due to commit e85aad4ae76 ("nat/x86-cpuid.h: Add x86_cpuid_count
> wrapper around __get_cpuid_count"), which introduced the nullptr check.
> 
> The header file gdb/nat/x86-cpuid.h is a file that is included in the build
> and compiled as a C++ file, but also in the testsuite and compiled as a C
> file.
> 
> Fix this by replacing nullptr with (void *)0.
> 
> Tested on x86_64-linux.

This seems obvious to me, please push.
  

On Tue, 29 Aug 2023 17:38:57 +0200
Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> wrote:

> When running test-case gdb.arch/i386-avx512.exp, I run into:
> ...
>  gdb compile failed, In file included from gdb.arch/i386-avx512.c:20:0:
>  src/gdb/nat/x86-cpuid.h: In function 'x86_cpuid_count':
>  src/gdb/nat/x86-cpuid.h:63:16: error: \
>    'nullptr' undeclared (first use in this function)
>     if (__eax == nullptr)
>                  ^~~~~~~
>  src/gdb/nat/x86-cpuid.h:63:16: note: each \
>    undeclared identifier is reported only once for each function it appears in
[...]
> This is due to commit e85aad4ae76 ("nat/x86-cpuid.h: Add x86_cpuid_count
> wrapper around __get_cpuid_count"), which introduced the nullptr check.
> 
> The header file gdb/nat/x86-cpuid.h is a file that is included in the build
> and compiled as a C++ file, but also in the testsuite and compiled as a C
> file.
> 
> Fix this by replacing nullptr with (void *)0.
[...]

> -  if (__eax == nullptr)
> +  if (__eax == (void *)0)
>      __eax = &__scratch;
> -  if (__ebx == nullptr)
> +  if (__ebx == (void *)0)
>      __ebx = &__scratch;
> -  if (__ecx == nullptr)
> +  if (__ecx == (void *)0)
>      __ecx = &__scratch;
> -  if (__edx == nullptr)
> +  if (__edx == (void *)0)
>      __edx = &__scratch;

Maybe leave nullptr in place and instead do something like this...

/* This header file is also used in C code for the gdb.arch/i386-avx512.exp
   test, so define nullptr to avoid a compile error during testing.  */
#ifndef __cplusplus
#define nullptr (void *) 0)
#endif

Kevin
  

On 8/29/23 18:03, Kevin Buettner wrote:
> On Tue, 29 Aug 2023 17:38:57 +0200
> Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> wrote:
> 
>> When running test-case gdb.arch/i386-avx512.exp, I run into:
>> ...
>>   gdb compile failed, In file included from gdb.arch/i386-avx512.c:20:0:
>>   src/gdb/nat/x86-cpuid.h: In function 'x86_cpuid_count':
>>   src/gdb/nat/x86-cpuid.h:63:16: error: \
>>     'nullptr' undeclared (first use in this function)
>>      if (__eax == nullptr)
>>                   ^~~~~~~
>>   src/gdb/nat/x86-cpuid.h:63:16: note: each \
>>     undeclared identifier is reported only once for each function it appears in
> [...]
>> This is due to commit e85aad4ae76 ("nat/x86-cpuid.h: Add x86_cpuid_count
>> wrapper around __get_cpuid_count"), which introduced the nullptr check.
>>
>> The header file gdb/nat/x86-cpuid.h is a file that is included in the build
>> and compiled as a C++ file, but also in the testsuite and compiled as a C
>> file.
>>
>> Fix this by replacing nullptr with (void *)0.
> [...]
> 
>> -  if (__eax == nullptr)
>> +  if (__eax == (void *)0)
>>       __eax = &__scratch;
>> -  if (__ebx == nullptr)
>> +  if (__ebx == (void *)0)
>>       __ebx = &__scratch;
>> -  if (__ecx == nullptr)
>> +  if (__ecx == (void *)0)
>>       __ecx = &__scratch;
>> -  if (__edx == nullptr)
>> +  if (__edx == (void *)0)
>>       __edx = &__scratch;
> 
> Maybe leave nullptr in place and instead do something like this...
> 
> /* This header file is also used in C code for the gdb.arch/i386-avx512.exp
>     test, so define nullptr to avoid a compile error during testing.  */
> #ifndef __cplusplus
> #define nullptr (void *) 0)
> #endif
> 

Hi Kevin,

thanks for the review.

I'll commit this v2 tomorrow, unless there are further comments.

Thanks,
- Tom
  

On Tue, 29 Aug 2023 19:59:28 +0200
Tom de Vries <tdevries@suse.de> wrote:

> I'll commit this v2 tomorrow, unless there are further comments.

The new version LGTM.

Approved-by: Kevin Buettner <kevinb@redhat.com>

Kevin