Re: [PATCH v4] Always define __USE_TIME_BITS64 when 64 bit time_t is used

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 15/03/24 18:33, DJ Delorie wrote:
> 
> Fun stuff first...
> 
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>> diff --git a/manual/maint.texi b/manual/maint.texi
>>  
>> +When @code{__TIMESIZE == 64} is set, @theglibc{} will also define the
>> +@code{__USE_TIME_BITS64}.  It is used by the Linux kernel ABI to set the
>> +expected @code{time_t} size used on some syscalls.
> 
> This part seems OK.
> 
>> +Also, to define whether
>> +the declarations are expanded to 64-bit @code{time_t} symbols (since not
>> +all ABIs do require such expansion), @theglibc{} will also define
>> +@code{__USE_TIME64_REDIRECTS}.
> 
> This part doesn't match the code, because it's in the __TIMESIZE==64
> section, and the code only sets it when __TIMESIZE==32:
> 
> #if defined __USE_TIME_BITS64 && __TIMESIZE == 32
> # define __USE_TIME64_REDIRECTS 1
> #endif
> 
> Perhaps you were thinking of _TIME_BITS==64, which is defined elsewhere?
> 
> _TIME_BITS is defined in creature.texi as a user-defined feature test macro...

Right, I will move it to creature.texi.  It makes more sense, since it
should be a user-visible macro (albeit in the implementation-defined
namespace).

> 
>> diff --git a/sysdeps/unix/sysv/linux/features-time64.h b/sysdeps/unix/sysv/linux/features-time64.h
> 
>>  # if _TIME_BITS == 64
>>  #  if ! defined (_FILE_OFFSET_BITS) || _FILE_OFFSET_BITS != 64
>>  #   error "_TIME_BITS=64 is allowed only with _FILE_OFFSET_BITS=64"
>> -#  elif __TIMESIZE == 32
>> -#   define __USE_TIME_BITS64	1
>>  #  endif
>> +#  define __USE_TIME_BITS64	1
> 
> If the user asks for 64-bit time, we honor it, whether __TIMESIZE is 32
> or 64.  Ok.
> 
> If the user asks for 32-bit time, we allow it, but need do nothing.  Ok.
> 
>>  # elif _TIME_BITS == 32
>>  #  if __TIMESIZE > 32
>>  #   error "_TIME_BITS=32 is not compatible with __TIMESIZE > 32"
>> @@ -34,4 +33,10 @@
>>  # else
>>  #  error Invalid _TIME_BITS value (can only be 32 or 64-bit)
>>  # endif
> 
> This is for when _TIME_BITS is not set:
> 
>> +#elif __TIMESIZE == 64
>> +# define __USE_TIME_BITS64      1
>> +#endif
> 
> So if the user does not specify _TIME_BITS, we default to 64-bit kabi
> for 64-bit time_t.  OK.
> 
>> +#if defined __USE_TIME_BITS64 && __TIMESIZE == 32
>> +# define __USE_TIME64_REDIRECTS 1
>>  #endif
> 
> If we want 64-bit time_t (for any reason) but the default time_t is 32
> bits, we need the redirected functions et al.  Ok.
> 
>> diff --git a/sysdeps/generic/features-time64.h b/sysdeps/generic/features-time64.h
>>  /* The generic configuration only support _TIME_BITS=32.  */
>> +#define __USE_TIME_BITS64       0
>> +/* The following macro defines whether the 64 time_t redirects will be
>> +   used for 64 bit aware symbols.  */
>> +#define __USE_TIME64_REDIRECTS  0
> 
> So the default for non-linux platforms is to not do any of the linux
> magic.  Ok.
> 
> And now for the mechanical part...
> 
>> diff --git a/io/bits/poll2.h b/io/bits/poll2.h
>> . . .
>> diff --git a/time/time.h b/time/time.h
> 
> They're all good :-)
>