Don't scrub the C stack from C.

[sbcl.git] / src / runtime / x86-assem.S

diff --git a/src/runtime/x86-assem.S b/src/runtime/x86-assem.S
index 2945f77..d6dd52b 100644 (file)
--- a/src/runtime/x86-assem.S
+++ b/src/runtime/x86-assem.S
@@ -881,6 +881,81 @@ Lend_base:
         pop %eax
        ret
        SIZE(GNAME(fast_bzero_base))
-        
-\f      
+
+\f
+/* When LISP_FEATURE_C_STACK_IS_CONTROL_STACK, we cannot safely scrub
+ * the control stack from C, largely due to not knowing where the
+ * active stack frame ends.  On such platforms, we reimplement the
+ * core scrubbing logic in assembly, in this case here:
+ */
+       .text
+       .align  align_16byte,0x90
+       .globl GNAME(arch_scrub_control_stack)
+       TYPE(GNAME(arch_scrub_control_stack))
+GNAME(arch_scrub_control_stack):
+       /* We are passed three parameters:
+        * A (struct thread *) at [ESP+4],
+        * the address of the guard page at [ESP+8], and
+        * the address of the hard guard page at [ESP+12].
+        * We may trash EAX, ECX, and EDX with impunity.
+        * [ESP] is our return address, [ESP-4] is the first
+        * stack slot to scrub. */
+
+       /* We start by setting up our scrub pointer in EAX, our
+        * guard page upper bound in ECX, and our hard guard
+        * page upper bound in EDX. */
+       lea     -4(%esp), %eax
+       mov     GNAME(os_vm_page_size),%edx
+       mov     %edx, %ecx
+       add     8(%esp), %ecx
+       add     12(%esp), %edx
+
+       /* We need to do a memory operation relative to the
+        * thread pointer, so put it in %ecx and our guard
+        * page upper bound in 4(%esp). */
+       xchg    4(%esp), %ecx
+
+       /* Now we begin our main scrub loop. */
+ascs_outer_loop:
+
+       /* If we're about to scrub the hard guard page, exit. */
+       cmp     %edx, %eax
+       jae     ascs_check_guard_page
+       cmp     12(%esp), %eax
+       ja      ascs_finished
+
+ascs_check_guard_page:
+       /* If we're about to scrub the guard page, and the guard
+        * page is protected, exit. */
+       cmp     4(%esp), %eax
+       jae     ascs_clear_loop
+       cmp     8(%esp), %eax
+       jbe     ascs_clear_loop
+       cmpl    $(NIL), THREAD_CONTROL_STACK_GUARD_PAGE_PROTECTED_OFFSET(%ecx)
+       jne     ascs_finished
+
+       /* Clear memory backwards to the start of the (4KiB) page */
+ascs_clear_loop:
+       movl    $0, (%eax)
+       test    $0xfff, %eax
+       lea     -4(%eax), %eax
+       jnz     ascs_clear_loop
+
+       /* If we're about to hit the hard guard page, exit. */
+       cmp     %edx, %eax
+       jae     ascs_finished
+
+       /* If the next (previous?) 4KiB page contains a non-zero
+        * word, continue scrubbing. */
+ascs_check_loop:
+       testl   $-1, (%eax)
+       jnz     ascs_outer_loop
+       test    $0xfff, %eax
+       lea     -4(%eax), %eax
+       jnz     ascs_check_loop
+
+ascs_finished:
+       ret
+       SIZE(GNAME(arch_scrub_control_stack))
+\f
         END()