Don't scrub the C stack from C.

[sbcl.git] / src / runtime / x86-64-assem.S

diff --git a/src/runtime/x86-64-assem.S b/src/runtime/x86-64-assem.S
index c4f5435..1fb7b00 100644 (file)
--- a/src/runtime/x86-64-assem.S
+++ b/src/runtime/x86-64-assem.S
@@ -458,4 +458,78 @@ Lend:
        ret
        SIZE(GNAME(fast_bzero))
 
+\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 *) in RDI,
+        * the address of the guard page in RSI, and
+        * the address of the hard guard page in RDX.
+        * We may trash RAX, RCX, and R8-R11 with impunity.
+        * [RSP] is our return address, [RSP-8] is the first
+        * stack slot to scrub. */
+
+       /* We start by setting up our scrub pointer in RAX, our
+        * guard page upper bound in R8, and our hard guard
+        * page upper bound in R9. */
+       lea     -8(%rsp), %rax
+#ifdef LISP_FEATURE_DARWIN
+       mov     GSYM(GNAME(os_vm_page_size)),%r9
+#else
+       mov     os_vm_page_size,%r9
+#endif
+       lea     (%rsi,%r9), %r8
+       lea     (%rdx,%r9), %r9
+
+       /* Now we begin our main scrub loop. */
+ascs_outer_loop:
+
+       /* If we're about to scrub the hard guard page, exit. */
+       cmp     %r9, %rax
+       jae     ascs_check_guard_page
+       cmp     %rax, %rdx
+       jbe     ascs_finished
+
+ascs_check_guard_page:
+       /* If we're about to scrub the guard page, and the guard
+        * page is protected, exit. */
+       cmp     %r8, %rax
+       jae     ascs_clear_loop
+       cmp     %rax, %rsi
+       ja      ascs_clear_loop
+       cmpq    $(NIL), THREAD_CONTROL_STACK_GUARD_PAGE_PROTECTED_OFFSET(%rdi)
+       jne     ascs_finished
+
+       /* Clear memory backwards to the start of the (4KiB) page */
+ascs_clear_loop:
+       movq    $0, (%rax)
+       test    $0xfff, %rax
+       lea     -8(%rax), %rax
+       jnz     ascs_clear_loop
+
+       /* If we're about to hit the hard guard page, exit. */
+       cmp     %r9, %rax
+       jae     ascs_finished
+
+       /* If the next (previous?) 4KiB page contains a non-zero
+        * word, continue scrubbing. */
+ascs_check_loop:
+       testq   $-1, (%rax)
+       jnz     ascs_outer_loop
+       test    $0xfff, %rax
+       lea     -8(%rax), %rax
+       jnz     ascs_check_loop
+
+ascs_finished:
+       ret
+       SIZE(GNAME(arch_scrub_control_stack))
+\f
         END()