Re: [PATCH v7 0/3] y2038: Linux: Introduce __clock_settime64 function

[Alistair Francis <alistair23 at gmail dot com>]

On Fri, Sep 6, 2019 at 2:28 PM Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Fri, 6 Sep 2019, Alistair Francis wrote:
>
> > Which I can fix with this diff:
>
> This diff is not the right way to fix this build failure.
>
> One of the design principles in the Y2038 support is that is __TIMESIZE ==
> 64, the time functions *aren't* trivial wrappers of time64 functions;
> rather, the time64 function definitions are remapped (via macros) so they
> define the function name with no "64".  For each case where there is a
> pair of functions (for different time_t types) in the __TIMESIZE == 32
> case, there should just be the one function when __TIMESIZE == 64.
>
> This ensures that the Y2038 changes don't add any overhead at all in the
> glibc binaries on existing platforms with __TIMESIZE == 64.
>
> You should look at exactly what the types in question are, that are being
> reported as conflicting in your build (probably by looking at preprocessed
> source).  __timespec64 and timespec are supposed to be the same type (via
> #define) when __TIMESIZE == 64, to avoid such incompatibilities.

Looking at the place where the__timespec64 is defined they aren't the
same for __TIMESIZE == 64 on a 32-bit system.

The code is below:

#if __WORDSIZE == 64 \
  || (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64)
# define __timespec64 timespec
#else
/* The glibc Y2038-proof struct __timespec64 structure for a time value.
   To keep things Posix-ish, we keep the nanoseconds field a 32-bit
   signed long, but since the Linux field is a 64-bit signed int, we
   pad our tv_nsec with a 32-bit int.

   As a general rule the Linux kernel is ignoring upper 32 bits of
   tv_nsec field.  */
struct __timespec64
{
  __time64_t tv_sec;         /* Seconds */
# if BYTE_ORDER == BIG_ENDIAN
  __int32_t tv_pad;          /* Padding */
  __int32_t tv_nsec;         /* Nanoseconds */
# else
  __int32_t tv_nsec;         /* Nanoseconds */
  __int32_t tv_pad;          /* Padding */
# endif
};
#endif

So looking at that with __TIMESIZE == 64 but __WORDSIZE == 32 (as on
RV32) we will specify a __timespec64 struct that is different to the
timespec struct.

Would the correct fix be to add __TIMESIZE == 64 to the #if mentioned above?

This diff fixes the build for me:

diff --git a/include/time.h b/include/time.h
index 5f7529f10e9..ff5f18ec56c 100644
--- a/include/time.h
+++ b/include/time.h
@@ -51,7 +51,8 @@ extern void __tz_compute (__time64_t timer, struct
tm *tm, int use_localtime)
   __THROW attribute_hidden;

 #if __WORDSIZE == 64 \
-  || (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64)
+  || (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64) || \
+  __TIMESIZE == 64
 # define __timespec64 timespec
 #else
 /* The glibc Y2038-proof struct __timespec64 structure for a time value.

Alistair

>
> --
> Joseph S. Myers
> joseph@codesourcery.com