merge revision(s) f336a3eb6c76890f3d8f878725b3d328c8fdcf33: [Backport #18126]

	Use free instead of xfree to free altstack

	The altstack memory of a thread may be free'ed even after the VM is
	destructed. After that, GC is no longer available, so calling xfree
	may lead to a segfault.

	This changeset uses the bare free function to free the altstack memory
	instead of xfree. [Bug #18126]
	---
	 signal.c  | 5 ++++-
	 vm_core.h | 2 +-
	 2 files changed, 5 insertions(+), 2 deletions(-)

1 files changed, 4 insertions, 1 deletions

diff --git a/signal.c b/signal.c
index 6eea6aabe2..c13bc19f1c 100644
--- a/signal.c
+++ b/signal.c
@@ -557,10 +557,13 @@ static int rb_sigaltstack_size_value = 0;
 void *
 rb_allocate_sigaltstack(void)
 {
+    void *altstack;
     if (!rb_sigaltstack_size_value) {
 	rb_sigaltstack_size_value = rb_sigaltstack_size();
     }
-    return xmalloc(rb_sigaltstack_size_value);
+    altstack = malloc(rb_sigaltstack_size_value);
+    if (!altstack) rb_memerror();
+    return altstack;
 }
 
 /* alternate stack for SIGSEGV */