gh-96652: Fix faulthandler chained signal without sigaction() (#96666)

vstinner · web-flow · commit c580a81af91a · 2022-09-08T12:20:22.000+02:00
Fix the faulthandler implementation of faulthandler.register(signal,
chain=True) if the sigaction() function is not available: don't call
the previous signal handler if it's NULL.
diff --git a/Misc/NEWS.d/next/Library/2022-09-07-22-49-37.gh-issue-96652.YqOKxI.rst b/Misc/NEWS.d/next/Library/2022-09-07-22-49-37.gh-issue-96652.YqOKxI.rst
@@ -0,0 +1,3 @@
+Fix the faulthandler implementation of ``faulthandler.register(signal,
+chain=True)`` if the ``sigaction()`` function is not available: don't call
+the previous signal handler if it's NULL. Patch by Victor Stinner.
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
@@ -862,7 +862,7 @@ faulthandler_user(int signum)
         errno = save_errno;
     }
 #else
-    if (user->chain) {
+    if (user->chain && user->previous != NULL) {
         errno = save_errno;
         /* call the previous signal handler */
         user->previous(signum);

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fix the faulthandler implementation of ``faulthandler.register(signal,
	`2`	+chain=True)`` if the ``sigaction()`` function is not available: don't call
	`3`	`+the previous signal handler if it's NULL. Patch by Victor Stinner.`
Original file line number	Diff line number	Diff line change
`@@ -862,7 +862,7 @@ faulthandler_user(int signum)`
`862`	`862`	`errno = save_errno;`
`863`	`863`	`}`
`864`	`864`	`#else`
`865`		`- if (user->chain) {`
	`865`	`+ if (user->chain && user->previous != NULL) {`
`866`	`866`	`errno = save_errno;`
`867`	`867`	`/* call the previous signal handler */`
`868`	`868`	`user->previous(signum);`