From 4e7bd2d06bd42686dcfbb8b4549c8535aaa50b00 Mon Sep 17 00:00:00 2001
From: Alejandro Colomar <alx.manpages@gmail.com>
Date: Sun, 8 Aug 2021 10:41:13 +0200
Subject: [PATCH] sigaction.2: Minor tweaks to Peter's patch

- Move example program to a new EXAMPLES section
- Invert logic in the handler to have the failure in the
  conditional path, and the success out of any conditionals.
- Use NULL, EXIT_SUCCESS, and EXIT_FAILURE instead of magic numbers
- Separate declarations from code
- Put function return type on its own line
- Put function opening brace on its line

Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
---
 man2/sigaction.2 | 76 +++++++++++++++++++++++++++---------------------
 1 file changed, 43 insertions(+), 33 deletions(-)

diff --git a/man2/sigaction.2 b/man2/sigaction.2
index 4bf6f095e..18404dde1 100644
--- a/man2/sigaction.2
+++ b/man2/sigaction.2
@@ -936,39 +936,6 @@ because they were introduced before Linux 5.11.
 However, in general, programs may assume that these flags are supported,
 since they have all been supported since Linux 2.6,
 which was released in the year 2003.
-.PP
-The following example program exits with status 0 if
-.B SA_EXPOSE_TAGBITS
-is determined to be supported, and 1 otherwise.
-.PP
-.EX
-#include <signal.h>
-#include <stdio.h>
-#include <unistd.h>
-
-void handler(int signo, siginfo_t *info, void *context) {
-    struct sigaction oldact;
-    if (sigaction(SIGSEGV, 0, &oldact) == 0 &&
-        !(oldact.sa_flags & SA_UNSUPPORTED) &&
-        (oldact.sa_flags & SA_EXPOSE_TAGBITS)) {
-        _exit(0);
-    } else {
-        _exit(1);
-    }
-}
-
-int main(void) {
-    struct sigaction act = {0};
-    act.sa_flags = SA_SIGINFO | SA_UNSUPPORTED | SA_EXPOSE_TAGBITS;
-    act.sa_sigaction = handler;
-    if (sigaction(SIGSEGV, &act, 0) != 0) {
-        perror("sigaction");
-        return 1;
-    }
-
-    raise(SIGSEGV);
-}
-.EE
 .SH RETURN VALUE
 .BR sigaction ()
 returns 0 on success; on error, \-1 is returned, and
@@ -1174,6 +1141,49 @@ This bug was fixed in kernel 2.6.14.
 .SH EXAMPLES
 See
 .BR mprotect (2).
+.PP
+The following example program exits with status
+.B EXIT_SUCCESS
+if
+.B SA_EXPOSE_TAGBITS
+is determined to be supported, and
+.B EXIT_FAILURE
+otherwise.
+.PP
+.EX
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+void
+handler(int signo, siginfo_t *info, void *context)
+{
+    struct sigaction oldact;
+
+    if (sigaction(SIGSEGV, NULL, &oldact) != 0 ||
+        (oldact.sa_flags & SA_UNSUPPORTED) ||
+        !(oldact.sa_flags & SA_EXPOSE_TAGBITS)) {
+        _exit(EXIT_FAILURE);
+    }
+    _exit(EXIT_SUCCESS);
+}
+
+int
+main(void)
+{
+    struct sigaction act = {0};
+
+    act.sa_flags = SA_SIGINFO | SA_UNSUPPORTED | SA_EXPOSE_TAGBITS;
+    act.sa_sigaction = &handler;
+    if (sigaction(SIGSEGV, &act, NULL) != 0) {
+        perror("sigaction");
+        exit(EXIT_FAILURE);
+    }
+
+    raise(SIGSEGV);
+}
+.EE
 .SH SEE ALSO
 .BR kill (1),
 .BR kill (2),