simplify altstack and enable reuse with thread cache

Instead of allocating and registering the altstack in different
places, do it together to reduce code and improve readability.
When thread cache is enabled, storing altstack in rb_thread_t
is wasteful and we may reuse altstack in the same pthread.

This also lets us clearly allow use of xmalloc to allow GC to
recover from ENOMEM.

[ruby-core:85621] [Feature #14487]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63213 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 10 deletions

diff --git a/signal.c b/signal.c
index 694661457b..5803f8f0b9 100644
--- a/signal.c
+++ b/signal.c
@@ -554,7 +554,7 @@ typedef RETSIGTYPE ruby_sigaction_t(int);
 #endif
 
 #ifdef USE_SIGALTSTACK
-int
+static int
 rb_sigaltstack_size(void)
 {
     /* XXX: BSD_vfprintf() uses >1500KiB stack and x86-64 need >5KiB stack. */
@@ -577,19 +577,18 @@ rb_sigaltstack_size(void)
 }
 
 /* alternate stack for SIGSEGV */
-void
-rb_register_sigaltstack(rb_thread_t *th)
+void *
+rb_register_sigaltstack(void)
 {
     stack_t newSS, oldSS;
 
-    if (!th->altstack)
-	rb_bug("rb_register_sigaltstack: th->altstack not initialized\n");
-
-    newSS.ss_sp = th->altstack;
     newSS.ss_size = rb_sigaltstack_size();
+    newSS.ss_sp = xmalloc(newSS.ss_size);
     newSS.ss_flags = 0;
 
     sigaltstack(&newSS, &oldSS); /* ignore error. */
+
+    return newSS.ss_sp;
 }
 #endif /* USE_SIGALTSTACK */
 
@@ -1532,9 +1531,7 @@ Init_signal(void)
 	install_sighandler(SIGILL, (sighandler_t)sigill);
 #endif
 #ifdef SIGSEGV
-# ifdef USE_SIGALTSTACK
-	rb_register_sigaltstack(GET_THREAD());
-# endif
+	RB_ALTSTACK_INIT(GET_VM()->main_altstack);
 	install_sighandler(SIGSEGV, (sighandler_t)sigsegv);
 #endif
     }