Add a configure test for gettid.

* configure.ac (HAVE_GETTID,HAVE_SYS_GETTID): New test.
* src/debug.c: Include syscall.h if needed.
(tid_log_callback) [HAVE_SYS_GETTID]: Use SYS_gettid
--

Linux introduced the gettid syscall with 2.4.11 but glibc only with
its version 2.30.  This patch allows building on older platforms.

Co-authored-by: lgh1

configure.ac

@@ -919,6 +919,25 @@ fi
 # Check for getgid etc
 AC_CHECK_FUNCS(getgid getegid closefrom nanosleep)
 
+# Check for gettid - test taken from strongswan git
+AC_CHECK_FUNC(gettid,
+       [AC_DEFINE(HAVE_GETTID, 1, [Defined if gettid is available.])],
+       [AC_MSG_CHECKING([for SYS_gettid])
+        AC_COMPILE_IFELSE(
+               [AC_LANG_PROGRAM(
+                       [[#define _GNU_SOURCE
+                         #include <unistd.h>
+                         #include <sys/syscall.h>
+                       ]],
+                       [[int main() {
+                         return syscall(SYS_gettid);}]])],
+               [AC_MSG_RESULT([yes])
+                AC_DEFINE(HAVE_SYS_GETTID,1,
+                         [Defined is the system call gettid is available])],
+               [AC_MSG_RESULT([no])]
+       )]
+)
+
 
 # Replacement functions.
 AC_REPLACE_FUNCS(stpcpy)

src/debug.c

@@ -29,6 +29,9 @@
 #ifdef HAVE_UNISTD_H
 # include <unistd.h>
 #endif
+#if defined(__linux) && defined(HAVE_SYS_GETTID)
+# include <syscall.h>
+#endif
 #include <ctype.h>
 #include <errno.h>
 #include <time.h>
@@ -147,12 +150,16 @@ static int
 tid_log_callback (unsigned long *rvalue)
 {
   int len = sizeof (*rvalue);
-  uintptr_t thread;
+  uintptr_t thread = 0;
 
 #ifdef HAVE_W32_SYSTEM
   thread = (uintptr_t)GetCurrentThreadId ();
 #elif defined(__linux)
-  thread = (uintptr_t)gettid ();
+#  ifdef HAVE_GETTID
+     thread = (uintptr_t)gettid ();
+#  elif defined(HAVE_SYS_GETTID)
+     thread = (uintptr_t)syscall(SYS_gettid);
+#  endif
 #endif
   if (sizeof (thread) < len)
     {