Modernize our code for looking up descriptive strings for Unix signals.

At least as far back as the 2008 spec, POSIX has defined strsignal(3)
for looking up descriptive strings for signal numbers.  We hadn't gotten
the word though, and were still using the crufty old sys_siglist array,
which is in no standard even though most Unixen provide it.

Aside from not being formally standards-compliant, this was just plain
ugly because it involved #ifdef's at every place using the code.

To eliminate the #ifdef's, create a portability function pg_strsignal,
which wraps strsignal(3) if available and otherwise falls back to
sys_siglist[] if available.  The set of Unixen with neither API is
probably empty these days, but on any platform with neither, you'll
just get "unrecognized signal".  All extant callers print the numeric
signal number too, so no need to work harder than that.

Along the way, upgrade pg_basebackup's child-error-exit reporting
to match the rest of the system.

Discussion: https://postgr.es/m/25758.1544983503@sss.pgh.pa.us

configure

@@ -15230,7 +15230,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in cbrt clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul symlink sync_file_range utime utimes wcstombs_l
+for ac_func in cbrt clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range utime utimes wcstombs_l
 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"

configure.in

@@ -1621,6 +1621,7 @@ AC_CHECK_FUNCS(m4_normalize([
 	setsid
 	shm_open
 	strchrnul
+	strsignal
 	symlink
 	sync_file_range
 	utime

src/backend/postmaster/pgarch.c

@@ -650,17 +650,10 @@ pgarch_archiveXlog(char *xlog)
 					 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
 					 errdetail("The failed archive command was: %s",
 							   xlogarchcmd)));
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
-			ereport(lev,
-					(errmsg("archive command was terminated by signal %d: %s",
-							WTERMSIG(rc),
-							WTERMSIG(rc) < NSIG ? sys_siglist[WTERMSIG(rc)] : "(unknown)"),
-					 errdetail("The failed archive command was: %s",
-							   xlogarchcmd)));
 #else
 			ereport(lev,
-					(errmsg("archive command was terminated by signal %d",
-							WTERMSIG(rc)),
+					(errmsg("archive command was terminated by signal %d: %s",
+							WTERMSIG(rc), pg_strsignal(WTERMSIG(rc))),
 					 errdetail("The failed archive command was: %s",
 							   xlogarchcmd)));
 #endif

src/backend/postmaster/postmaster.c

@@ -3612,6 +3612,7 @@ LogChildExit(int lev, const char *procname, int pid, int exitstatus)
 						procname, pid, WEXITSTATUS(exitstatus)),
 				 activity ? errdetail("Failed process was running: %s", activity) : 0));
 	else if (WIFSIGNALED(exitstatus))
+	{
 #if defined(WIN32)
 		ereport(lev,
 
@@ -3622,7 +3623,7 @@ LogChildExit(int lev, const char *procname, int pid, int exitstatus)
 						procname, pid, WTERMSIG(exitstatus)),
 				 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
 				 activity ? errdetail("Failed process was running: %s", activity) : 0));
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
+#else
 		ereport(lev,
 
 		/*------
@@ -3630,19 +3631,10 @@ LogChildExit(int lev, const char *procname, int pid, int exitstatus)
 		  "server process" */
 				(errmsg("%s (PID %d) was terminated by signal %d: %s",
 						procname, pid, WTERMSIG(exitstatus),
-						WTERMSIG(exitstatus) < NSIG ?
-						sys_siglist[WTERMSIG(exitstatus)] : "(unknown)"),
-				 activity ? errdetail("Failed process was running: %s", activity) : 0));
-#else
-		ereport(lev,
-
-		/*------
-		  translator: %s is a noun phrase describing a child process, such as
-		  "server process" */
-				(errmsg("%s (PID %d) was terminated by signal %d",
-						procname, pid, WTERMSIG(exitstatus)),
+						pg_strsignal(WTERMSIG(exitstatus))),
 				 activity ? errdetail("Failed process was running: %s", activity) : 0));
 #endif
+	}
 	else
 		ereport(lev,
 

src/bin/pg_basebackup/pg_basebackup.c

@@ -2066,7 +2066,7 @@ BaseBackup(void)
 	{
 #ifndef WIN32
 		int			status;
-		int			r;
+		pid_t		r;
 #else
 		DWORD		status;
 
@@ -2094,7 +2094,7 @@ BaseBackup(void)
 
 		/* Just wait for the background process to exit */
 		r = waitpid(bgchild, &status, 0);
-		if (r == -1)
+		if (r == (pid_t) -1)
 		{
 			fprintf(stderr, _("%s: could not wait for child process: %s\n"),
 					progname, strerror(errno));
@@ -2103,19 +2103,13 @@ BaseBackup(void)
 		if (r != bgchild)
 		{
 			fprintf(stderr, _("%s: child %d died, expected %d\n"),
-					progname, r, (int) bgchild);
+					progname, (int) r, (int) bgchild);
 			disconnect_and_exit(1);
 		}
-		if (!WIFEXITED(status))
-		{
-			fprintf(stderr, _("%s: child process did not exit normally\n"),
-					progname);
-			disconnect_and_exit(1);
-		}
-		if (WEXITSTATUS(status) != 0)
+		if (status != 0)
 		{
-			fprintf(stderr, _("%s: child process exited with error %d\n"),
-					progname, WEXITSTATUS(status));
+			fprintf(stderr, "%s: %s\n",
+					progname, wait_result_to_str(status));
 			disconnect_and_exit(1);
 		}
 		/* Exited normally, we're happy! */

src/common/wait_error.c

@@ -56,25 +56,17 @@ wait_result_to_str(int exitstatus)
 		}
 	}
 	else if (WIFSIGNALED(exitstatus))
+	{
 #if defined(WIN32)
 		snprintf(str, sizeof(str),
 				 _("child process was terminated by exception 0x%X"),
 				 WTERMSIG(exitstatus));
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
-	{
-		char		str2[256];
-
-		snprintf(str2, sizeof(str2), "%d: %s", WTERMSIG(exitstatus),
-				 WTERMSIG(exitstatus) < NSIG ?
-				 sys_siglist[WTERMSIG(exitstatus)] : "(unknown)");
-		snprintf(str, sizeof(str),
-				 _("child process was terminated by signal %s"), str2);
-	}
 #else
 		snprintf(str, sizeof(str),
-				 _("child process was terminated by signal %d"),
-				 WTERMSIG(exitstatus));
+				 _("child process was terminated by signal %d: %s"),
+				 WTERMSIG(exitstatus), pg_strsignal(WTERMSIG(exitstatus)));
 #endif
+	}
 	else
 		snprintf(str, sizeof(str),
 				 _("child process exited with unrecognized status %d"),

src/include/pg_config.h.in

@@ -559,6 +559,9 @@
 /* Define to use have a strong random number source */
 #undef HAVE_STRONG_RANDOM
 
+/* Define to 1 if you have the `strsignal' function. */
+#undef HAVE_STRSIGNAL
+
 /* Define to 1 if you have the `strtoll' function. */
 #undef HAVE_STRTOLL
 

src/include/pg_config.h.win32

@@ -415,6 +415,9 @@
 /* Define to use have a strong random number source */
 #define HAVE_STRONG_RANDOM 1
 
+/* Define to 1 if you have the `strsignal' function. */
+/* #undef HAVE_STRSIGNAL */
+
 /* Define to 1 if you have the `strtoll' function. */
 #ifdef HAVE_LONG_LONG_INT_64
 #define HAVE_STRTOLL 1

src/include/port.h

@@ -209,6 +209,9 @@ extern char *pg_strerror_r(int errnum, char *buf, size_t buflen);
 #define strerror_r pg_strerror_r
 #define PG_STRERROR_R_BUFLEN 256	/* Recommended buffer size for strerror_r */
 
+/* Wrap strsignal(), or provide our own version if necessary */
+extern const char *pg_strsignal(int signum);
+
 /* Portable prompt handling */
 extern void simple_prompt(const char *prompt, char *destination, size_t destlen,
 			  bool echo);

src/port/Makefile

@@ -37,7 +37,7 @@ LIBS += $(PTHREAD_LIBS)
 
 OBJS = $(LIBOBJS) $(PG_CRC32C_OBJS) chklocale.o erand48.o inet_net_ntop.o \
 	noblock.o path.o pgcheckdir.o pgmkdirp.o pgsleep.o \
-	pgstrcasecmp.o pqsignal.o \
+	pgstrcasecmp.o pgstrsignal.o pqsignal.o \
 	qsort.o qsort_arg.o quotes.o snprintf.o sprompt.o strerror.o \
 	tar.o thread.o
 

src/port/pgstrsignal.c

+/*-------------------------------------------------------------------------
+ *
+ * pgstrsignal.c
+ *	  Identify a Unix signal number
+ *
+ * On platforms compliant with modern POSIX, this just wraps strsignal(3).
+ * Elsewhere, we do the best we can.
+ *
+ * This file is not currently built in MSVC builds, since it's useless
+ * on non-Unix platforms.
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/port/pgstrsignal.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+
+/*
+ * pg_strsignal
+ *
+ * Return a string identifying the given Unix signal number.
+ *
+ * The result is declared "const char *" because callers should not
+ * modify the string.  Note, however, that POSIX does not promise that
+ * the string will remain valid across later calls to strsignal().
+ *
+ * This version guarantees to return a non-NULL pointer, although
+ * some platforms' versions of strsignal() do not.
+ */
+const char *
+pg_strsignal(int signum)
+{
+	const char *result;
+
+	/*
+	 * If we have strsignal(3), use that --- but check its result for NULL.
+	 * Otherwise, if we have sys_siglist[], use that; just out of paranoia,
+	 * check for NULL there too.  (We assume there is no point in trying both
+	 * APIs.)
+	 */
+#if defined(HAVE_STRSIGNAL)
+	result = strsignal(signum);
+	if (result)
+		return result;
+#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
+	if (signum > 0 && signum < NSIG)
+	{
+		result = sys_siglist[signum];
+		if (result)
+			return result;
+	}
+#endif
+
+	/*
+	 * Fallback case: just return "unrecognized signal".  Project style is for
+	 * callers to print the numeric signal value along with the result of this
+	 * function, so there's no need to work harder than this.
+	 */
+	result = "unrecognized signal";
+	return result;
+}

src/test/regress/pg_regress.c

@@ -1560,14 +1560,9 @@ log_child_failure(int exitstatus)
 #if defined(WIN32)
 		status(_(" (test process was terminated by exception 0x%X)"),
 			   WTERMSIG(exitstatus));
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
-		status(_(" (test process was terminated by signal %d: %s)"),
-			   WTERMSIG(exitstatus),
-			   WTERMSIG(exitstatus) < NSIG ?
-			   sys_siglist[WTERMSIG(exitstatus)] : "(unknown))");
 #else
-		status(_(" (test process was terminated by signal %d)"),
-			   WTERMSIG(exitstatus));
+		status(_(" (test process was terminated by signal %d: %s)"),
+			   WTERMSIG(exitstatus), pg_strsignal(WTERMSIG(exitstatus)));
 #endif
 	}
 	else