Use strerror_r in safe_strerror if available

Also stores the result in a thread-local static variable and
changes the return value to a const char*.

This is already important because Guile creates threads and
Python can create threads, but with the patch series here:
https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/176
GDB itself will create threads, too.

gdb/ChangeLog:

2019-10-31  Christian Biesinger  <cbiesinger@google.com>

	* configure: Regenerate.
	* configure.ac: Check for strerror_r.
	* gdbsupport/common-utils.h (safe_strerror): Change return value
	to const char * and document that this function is now threadsafe.
	* gdbsupport/posix-strerror.c (safe_strerror): Make buf
	thread_local and call strerror_r, if available.
	* utils.c (perror_string): Update.
	(print_sys_errmsg): Update.

Change-Id: I81048fbaf148035c221c528727f7efe58ba528eb

2 files changed, 17 insertions, 7 deletions

diff --git a/gdb/gdbsupport/common-utils.h b/gdb/gdbsupport/common-utils.h
index 23bf354..89868fc 100644
--- a/gdb/gdbsupport/common-utils.h
+++ b/gdb/gdbsupport/common-utils.h
@@ -108,9 +108,9 @@ std::string extract_string_maybe_quoted (const char **arg);
 
 /* The strerror() function can return NULL for errno values that are
    out of range.  Provide a "safe" version that always returns a
-   printable string.  */
+   printable string.  This version is also thread-safe.  */
 
-extern char *safe_strerror (int);
+extern const char *safe_strerror (int);
 
 /* Return true if the start of STRING matches PATTERN, false otherwise.  */
 
diff --git a/gdb/gdbsupport/posix-strerror.c b/gdb/gdbsupport/posix-strerror.c
index a8651b7..34420cf 100644
--- a/gdb/gdbsupport/posix-strerror.c
+++ b/gdb/gdbsupport/posix-strerror.c
@@ -21,15 +21,25 @@
 
 /* Implementation of safe_strerror as defined in common-utils.h.  */
 
-char *
+const char *
 safe_strerror (int errnum)
 {
-  char *msg;
-
+  static thread_local char buf[1024];
+
+  char *msg = nullptr;
+#ifdef HAVE_STRERROR_R
+#  if !__GLIBC__ || ((_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE)
+  /* Glibc has two different, incompatible versions of strerror_r.  */
+  if (strerror_r (errnum, buf, sizeof (buf)) == 0)
+    msg = buf;
+#  else
+  msg = strerror_r (errnum, buf, sizeof (buf));
+#  endif
+#else
   msg = strerror (errnum);
-  if (msg == NULL)
+#endif
+  if (msg == nullptr)
     {
-      static char buf[32];
 
       xsnprintf (buf, sizeof buf, "(undocumented errno %d)", errnum);
       msg = buf;