Changeset 11414

Timestamp:

Nov 19, 2008, 6:25:17 AM (11 years ago)

Author:

rme

Message:

In ALLOC-C-FRAME and ALLOC-VARIABLE-C-FRAME, enforce a minimum frame
size of 24 bytes. GCC on Darwin seems to do this (a non-leaf C
function with no locals seems to reserve 24 bytes). If this is
part of the ABI, it's not mentioned anywhere...

This issue came up in the context of this call: (#_open pathname
#$O_RDONLY). On entry to the C library routine, the stack contains
the return address, pathname, and flags. The routine sets a bit
in the (nominally optional) third argument (the file mode). This
clobbers the C frame link, since we only passed two args.

Since open(2) has a variadic prototype, I suppose that in C, this would
result in there always being a 0 on the stack in the position of
the mode argument (with two-arg open), so that would make _open safe, too.
(In the three-arg case, there'd be a 0 after the third arg, of course.)

File:

• trunk/source/compiler/X86/X8632/x8632-vinsns.lisp (modified) (2 diffs)

trunk/source/compiler/X86/X8632/x8632-vinsns.lisp

@@ -3686 +3686 @@
                                    ((temp :imm)))
   (movd (:@ (:%seg :rcontext) x8632::tcr.foreign-sp) (:%mmx x8632::stack-temp))
-  (subl (:$l (:apply ash nwords x8632::word-shift))
+  ;; make frame at least 24 bytes long
+  (subl (:$l (:apply ash (:apply max 6 nwords) x8632::word-shift))
         (:@ (:%seg :rcontext) x8632::tcr.foreign-sp))
   ;; align stack to 16-byte boundary
@@ -3699 +3700 @@
                                             ((temp :imm)))
   (movd (:@ (:%seg :rcontext) x8632::tcr.foreign-sp) (:%mmx x8632::stack-temp))
-  (subl (:%l nwords) (:@ (:%seg :rcontext) x8632::tcr.foreign-sp))
+  ;; make frame at least 24 bytes long (note that nwords is a fixnum)
+  (movl (:$l 24) (:%l temp))
+  (rcmpl (:%l nwords) (:%l temp))
+  (cmoval (:%l nwords) (:%l temp))
+  (subl (:%l temp) (:@ (:%seg :rcontext) x8632::tcr.foreign-sp))
   ;; align stack to 16-byte boundary
   (andb (:$b -16) (:@ (:%seg :rcontext) x8632::tcr.foreign-sp))