[libc-commits] [libc] [libc] Fix alarm layout mismatch on 32-bit time64 (PR #201276)

[Eli Friedman via libc-commits]

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@@ -30,16 +30,29 @@ LLVM_LIBC_FUNCTION(unsigned int, alarm, (unsigned int seconds)) {
   return static_cast<unsigned int>(
       LIBC_NAMESPACE::syscall_impl<long>(SYS_alarm, seconds));
 #elif defined(SYS_setitimer)
-  struct itimerval itv, old_itv;
-  itv.it_interval.tv_sec = 0;
-  itv.it_interval.tv_usec = 0;
-  itv.it_value.tv_sec = seconds;
-  itv.it_value.tv_usec = 0;
-  if (LIBC_NAMESPACE::syscall_impl<int>(SYS_setitimer, 0 /* ITIMER_REAL */,
-                                        &itv, &old_itv) < 0)
-    return 0;
-  return static_cast<unsigned int>(old_itv.it_value.tv_sec +
-                                   (old_itv.it_value.tv_usec > 0 ? 1 : 0));
+  // On 32-bit architectures with 64-bit time_t, SYS_setitimer still expects
+  // 32-bit fields. We must convert itimerval to use 32-bit fields.
+  if constexpr (sizeof(time_t) > sizeof(long)) {
+    long itv32[4] = {0, 0, static_cast<long>(seconds), 0};
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efriedma-quic wrote:

Do we need to handle overflow?  (The API takes an unsigned 32-bit integer, and this casts it to a signed 32-bit integer.)

https://github.com/llvm/llvm-project/pull/201276