[gcc r11-5167] libstdc++: Fix overflow checks to use the correct "time_t" [PR 93456]

[gcc r11-5167] libstdc++: Fix overflow checks to use the correct "time_t" [PR 93456]

[Jonathan Wakely]

https://gcc.gnu.org/g:b108faa9400e13a3d00dd7f71cff0ac45e29c5c9

commit r11-5167-gb108faa9400e13a3d00dd7f71cff0ac45e29c5c9
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 19 13:33:11 2020 +0000

    libstdc++: Fix overflow checks to use the correct "time_t" [PR 93456]
    
    I recently added overflow checks to src/c++11/futex.cc for PR 93456, but
    then changed the type of the timespec for PR 93421. This meant the
    overflow checks were no longer using the right range, because the
    variable being written to might be smaller than time_t.
    
    This introduces new typedef that corresponds to the tv_sec member of the
    struct being passed to the syscall, and uses that typedef in the range
    checks.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/93421
            PR libstdc++/93456
            * src/c++11/futex.cc (syscall_time_t): New typedef for
            the type of the syscall_timespec::tv_sec member.
            (relative_timespec, _M_futex_wait_until)
            (_M_futex_wait_until_steady): Use syscall_time_t in overflow
            checks, not time_t.

Diff:
---
 libstdc++-v3/src/c++11/futex.cc | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index 33e2097e19c..290201ae254 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -64,8 +64,10 @@ namespace
   // 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; };
+  using syscall_time_t = long;
 #else
   using syscall_timespec = ::timespec;
+  using syscall_time_t = time_t;
 #endif
 
   // Return the relative duration from (now_s + now_ns) to (abs_s + abs_ns)
@@ -86,9 +88,9 @@ namespace
     const auto rel_s = abs_s.count() - now_s;
 
     // Convert the absolute timeout to a relative timeout, without overflow.
-    if (rel_s > __int_traits<time_t>::__max) [[unlikely]]
+    if (rel_s > __int_traits<syscall_time_t>::__max) [[unlikely]]
       {
-	rt.tv_sec = __int_traits<time_t>::__max;
+	rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	rt.tv_nsec = 999999999;
       }
     else
@@ -130,8 +132,8 @@ namespace
 	      return false;
 
 	    syscall_timespec rt;
-	    if (__s.count() > __int_traits<time_t>::__max) [[unlikely]]
-	      rt.tv_sec = __int_traits<time_t>::__max;
+	    if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
+	      rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	    else
 	      rt.tv_sec = __s.count();
 	    rt.tv_nsec = __ns.count();
@@ -206,8 +208,8 @@ namespace
 	      return false;
 
 	    syscall_timespec rt;
-	    if (__s.count() > __int_traits<time_t>::__max) [[unlikely]]
-	      rt.tv_sec = __int_traits<time_t>::__max;
+	    if (__s.count() > __int_traits<syscall_time_t>::__max) [[unlikely]]
+	      rt.tv_sec = __int_traits<syscall_time_t>::__max;
 	    else
 	      rt.tv_sec = __s.count();
 	    rt.tv_nsec = __ns.count();