[issue21131] test_faulthandler.test_register_chain fails on 64bit ppc/arm with kernel >= 3.10

[STINNER Victor]

STINNER Victor <vstinner at redhat.com> added the comment:

I dislike PR 13649 because it touch the thread module, only to fix a faulthandler unit test. The relationship between thread stack size and faulthandler is not obvious to me. Currently, faulthandler uses SIGSTKSZ, not the thread stack size. faulthandler usage of the stack should be quite low: it should need less than 1 MiB for example.

"When faulthandler.c uses sigaltstack(2), the stack size is set up with a buffer of size SIGSTKSZ. That is, sadly, only 8k."

"A chained signal handler that needs to invoke dynamic linking will therefore consume more than the default stack space allocated in faulthandler.c, just in machine-state saves alone. So, the failing test is failing because its scribbling on random memory before the allocated stack space."

Aha, that's interesting: SIGSTKSZ should be enough for 1 signal handler, but test_register_chain calls 2 signal handlers using the same stack. Can you please try the following patch?

diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index 2331051f79..e7d13f2b2d 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -1325,7 +1325,7 @@ _PyFaulthandler_Init(int enable)
      * be able to allocate memory on the stack, even on a stack overflow. If it
      * fails, ignore the error. */
     stack.ss_flags = 0;
-    stack.ss_size = SIGSTKSZ;
+    stack.ss_size = SIGSTKSZ * 2;
     stack.ss_sp = PyMem_Malloc(stack.ss_size);
     if (stack.ss_sp != NULL) {
         err = sigaltstack(&stack, &old_stack);

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