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

gdb/ChangeLog

@@ -1,3 +1,14 @@
+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.
+
 2019-10-31  Luis Machado  <luis.machado@linaro.org>
 
 	* arm-tdep.c (arm_exidx_data_key): Use bfd_key instead of

gdb/configure

@@ -13073,7 +13073,7 @@ for ac_func in getauxval getrusage getuid getgid \
 		sigaction sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid \
-		ptrace64 sigaltstack setns use_default_colors
+		ptrace64 sigaltstack setns use_default_colors strerror_r
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

gdb/configure.ac

@@ -1318,7 +1318,7 @@ AC_CHECK_FUNCS([getauxval getrusage getuid getgid \
 		sigaction sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid \
-		ptrace64 sigaltstack setns use_default_colors])
+		ptrace64 sigaltstack setns use_default_colors strerror_r])
 AM_LANGINFO_CODESET
 GDB_AC_COMMON
 

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.  */
 

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;

gdb/utils.c

@@ -582,9 +582,7 @@ add_internal_problem_command (struct internal_problem *problem)
 static std::string
 perror_string (const char *prefix)
 {
-  char *err;
-
-  err = safe_strerror (errno);
+  const char *err = safe_strerror (errno);
   return std::string (prefix) + ": " + err;
 }
 
@@ -630,11 +628,8 @@ perror_warning_with_name (const char *string)
 void
 print_sys_errmsg (const char *string, int errcode)
 {
-  char *err;
-  char *combined;
-
-  err = safe_strerror (errcode);
-  combined = (char *) alloca (strlen (err) + strlen (string) + 3);
+  const char *err = safe_strerror (errcode);
+  char *combined = (char *) alloca (strlen (err) + strlen (string) + 3);
   strcpy (combined, string);
   strcat (combined, ": ");
   strcat (combined, err);