[PATCH] uml skas0: stop gcc's insanity

With Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

UML skas0 stub has been miscompiling for many people (incidentally not
the authors), depending on the used GCC versions.

I think (and testing on some GCC versions shows) this patch avoids the
fundamental issue which is behind this, namely gcc using the stack when
we have just replaced it, behind gcc's back.  The remapping and storage
of the return value is hidden in a blob of asm, hopefully giving gcc no
room for creativity.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 13 insertions, 10 deletions

diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index cb37ce9124a6..47b812b3bca8 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -18,11 +18,10 @@
  * on some systems.
  */
 
-#define STUB_DATA(field) (((struct stub_data *) UML_CONFIG_STUB_DATA)->field)
-
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_clone_handler(void)
 {
+        struct stub_data *data = (struct stub_data *) UML_CONFIG_STUB_DATA;
         long err;
 
         err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
@@ -35,17 +34,21 @@ stub_clone_handler(void)
         if(err)
                 goto out;
 
-        err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL,
-                            (long) &STUB_DATA(timer), 0);
+        err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL, 
+                            (long) &data->timer, 0);
         if(err)
                 goto out;
 
-        err = stub_syscall6(STUB_MMAP_NR, UML_CONFIG_STUB_DATA,
-                            UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
-                            MAP_FIXED | MAP_SHARED, STUB_DATA(fd),
-                            STUB_DATA(offset));
+        remap_stack(data->fd, data->offset);
+        goto done;
+
  out:
-        /* save current result. Parent: pid; child: retcode of mmap */
-        STUB_DATA(err) = err;
+        /* save current result. 
+         * Parent: pid; 
+         * child: retcode of mmap already saved and it jumps around this 
+         * assignment
+         */
+        data->err = err;
+ done:
         trap_myself();
 }