use sys_errlist[] in signal handler instead

of non Async-Signal-Safe strerror_r()

auto/unix

@@ -133,6 +133,16 @@ ngx_feature_test="char buf[1024]; long n; n = strerror_r(1, buf, 1024);
 . auto/feature
 
 
+ngx_feature="sys_errlist[]"
+ngx_feature_name="NGX_HAVE_SYS_ERRLIST"
+ngx_feature_run=yes
+ngx_feature_incs="#include <stdio.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="int n = sys_nerr; const char *p = sys_errlist[1];"
+. auto/feature
+
+
 ngx_feature="localtime_r()"
 ngx_feature_name="NGX_HAVE_LOCALTIME_R"
 ngx_feature_run=no

src/os/unix/ngx_errno.h

@@ -64,10 +64,22 @@ u_char *ngx_strerror_r(int err, u_char *errstr, size_t size);
 
 /* Solaris and Tru64 UNIX have thread-safe strerror() */
 
-#define ngx_strerror_r(err, errstr, size)  \
+#define ngx_strerror_r(err, errstr, size)                                    \
     ngx_cpystrn(errstr, (u_char *) strerror(err), size)
 
 #endif
 
 
+#if (NGX_HAVE_SYS_ERRLIST)
+
+#define ngx_sigsafe_strerror(err)                                            \
+    (err > 0 && err < sys_nerr) ? sys_errlist[err] : "Unknown error"
+
+#else
+
+#define ngx_sigsafe_strerror(err)  ""
+
+#endif
+
+
 #endif /* _NGX_ERRNO_H_INCLUDED_ */

src/os/unix/ngx_process.c

@@ -479,16 +479,17 @@ ngx_process_get_status(void)
              */
 
             if (err == NGX_ECHILD) {
-                ngx_log_error(NGX_LOG_INFO, ngx_cycle->log, errno,
+                ngx_log_error(NGX_LOG_INFO, ngx_cycle->log, 0,
-                              "waitpid() failed");
+                              "waitpid() failed (%d: %s)",
+                              err, ngx_sigsafe_strerror(err));
                 return;
             }
 
 #endif
 
-            ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, errno,
+            ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, 0,
-                          "waitpid() failed");
+                          "waitpid() failed (%d: %s)",
-
+                          err, ngx_sigsafe_strerror(err));
             return;
         }