libstdc++: Revert changes for SYS_clock_gettime64 [PR 93421]

As discussed in the PR, it's incredibly unlikely that a system that
needs to use the SYS_clock_gettime syscall (e.g. glibc 2.16 or older) is
going to define the SYS_clock_gettime64 macro. Ancient systems that need
to use the syscall aren't going to have time64 support.

This reverts the recent changes to try and make clock_gettime syscalls
be compatible with systems that have been updated for time64 (those
changes were wrong anyway as they misspelled the SYS_clock_gettime64
macro). The changes for futex syscalls are retained, because we still
use them on modern systems that might be using time64.

To ensure that the clock_gettime syscalls are safe, configure will fail
if SYS_clock_gettime is needed, and SYS_clock_gettime64 is also defined
(but to a distinct value from SYS_clock_gettime), and the tv_sec member
of timespec is larger than long. This means we will be unable to build
on a hypothetical system where we need the time32 version of
SYS_clock_gettime but where userspace is using a time64 struct timespec.
In the unlikely event that this failure is triggered on any real
systems, we can fix it later. But we probably won't need to.

libstdc++-v3/ChangeLog:

	PR libstdc++/93421
	* acinclude.m4 (GLIBCXX_ENABLE_LIBSTDCXX_TIME): Fail if struct
	timespec isn't compatible with SYS_clock_gettime.
	* configure: Regenerate.
	* src/c++11/chrono.cc: Revert changes for time64 compatibility.
	Add static_assert instead.
	* src/c++11/futex.cc (_M_futex_wait_until_steady): Assume
	SYS_clock_gettime can use struct timespec.

2 files changed, 5 insertions, 19 deletions

diff --git a/libstdc++-v3/src/c++11/chrono.cc b/libstdc++-v3/src/c++11/chrono.cc
index f10be7d..723f300 100644
--- a/libstdc++-v3/src/c++11/chrono.cc
+++ b/libstdc++-v3/src/c++11/chrono.cc
@@ -35,17 +35,6 @@
 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
 #include <unistd.h>
 #include <sys/syscall.h>
-
-# if defined(SYS_clock_gettime_time64) \
-  && SYS_clock_gettime_time64 != SYS_clock_gettime
-  // Userspace knows about the new time64 syscalls, so it's possible that
-  // userspace has also updated timespec to use a 64-bit tv_sec.
-  // The SYS_clock_gettime syscall still uses the old definition
-  // of timespec where tv_sec is 32 bits, so define a type that matches that.
-  struct syscall_timespec { long tv_sec; long tv_nsec; };
-# else
-  using syscall_timespec = ::timespec;
-# endif
 #endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
@@ -63,12 +52,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     system_clock::now() noexcept
     {
 #ifdef _GLIBCXX_USE_CLOCK_REALTIME
+      timespec tp;
       // -EINVAL, -EFAULT
 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
-      syscall_timespec tp;
       syscall(SYS_clock_gettime, CLOCK_REALTIME, &tp);
 #else
-      timespec tp;
       clock_gettime(CLOCK_REALTIME, &tp);
 #endif
       return time_point(duration(chrono::seconds(tp.tv_sec)
@@ -92,12 +80,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     steady_clock::now() noexcept
     {
 #ifdef _GLIBCXX_USE_CLOCK_MONOTONIC
+      timespec tp;
       // -EINVAL, -EFAULT
 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
-      syscall_timespec tp;
       syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &tp);
 #else
-      timespec tp;
       clock_gettime(CLOCK_MONOTONIC, &tp);
 #endif
       return time_point(duration(chrono::seconds(tp.tv_sec)
diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index 9adfb89..33e2097 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -61,8 +61,8 @@ namespace
 #if defined(SYS_futex_time64) && SYS_futex_time64 != SYS_futex
   // Userspace knows about the new time64 syscalls, so it's possible that
   // userspace has also updated timespec to use a 64-bit tv_sec.
-  // The SYS_futex and SYS_clock_gettime syscalls still use the old definition
-  // of timespec where tv_sec is 32 bits, so define a type that matches that.
+  // The SYS_futex syscall still uses the old definition of timespec
+  // where tv_sec is 32 bits, so define a type that matches that.
   struct syscall_timespec { long tv_sec; long tv_nsec; };
 #else
   using syscall_timespec = ::timespec;
@@ -234,11 +234,10 @@ namespace
 
 	// We only get to here if futex_clock_monotonic_unavailable was
 	// true or has just been set to true.
+	struct timespec ts;
 #ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
-	syscall_timespec ts;
 	syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts);
 #else
-	struct timespec ts;
 	clock_gettime(CLOCK_MONOTONIC, &ts);
 #endif