Changeset 14692 for trunk/source

Timestamp:

Mar 22, 2011, 9:40:43 PM (10 years ago)

Author:

gb

Message:

Try to reserve a little more space at the bottom of the altstack
on Linux to avoid SIGBUS on newer Linux kernels.

File:

• trunk/source/lisp-kernel/x86-exceptions.c (modified) (1 diff)

trunk/source/lisp-kernel/x86-exceptions.c

@@ -2373 +2373 @@
   stack.ss_flags = 0;
   mmap(stack.ss_sp,stack.ss_size, PROT_READ|PROT_WRITE|PROT_EXEC,MAP_FIXED|MAP_ANON|MAP_PRIVATE,-1,0);
+#ifdef LINUX
+  /* The ucontext pushed on the altstack may not contain the (largish)
+     __fpregs_mem field; copy_ucontext() wants to copy what it thinks
+     is a pointer to a full ucontext.  That'll touch a page beyond the
+     bottom of the altstack, and when this happens on the initial
+     thread's stack on a recent (2.6.32+?) kernel, we'll SIGBUS instead
+     of mapping that page.
+     It's easier to just reserve that page here than it would be to
+     change copy_ucontext().
+  */
+  stack.ss_size -= sizeof(struct ucontext);
+#endif
   if (sigaltstack(&stack, NULL) != 0) {
     perror("sigaltstack");