[PATCH] uml: implement {get,set}_thread_area for i386

Implement sys_[gs]et_thread_area and the corresponding ptrace operations for
UML.  This is the main chunk, additional parts follow.  This implementation is
now well tested and has run reliably for some time, and we've understood all
the previously existing problems.

Their implementation saves the new GDT content and then forwards the call to
the host when appropriate, i.e.  immediately when the target process is
running or on context switch otherwise (i.e.  on fork and on ptrace() calls).

In SKAS mode, we must switch registers on each context switch (because SKAS
does not switches tls_array together with current->mm).

Also, added get_cpu() locking; this has been done for SKAS mode, since TT does
not need it (it does not use smp_processor_id()).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/um/sys-i386/syscalls.c b/arch/um/sys-i386/syscalls.c
index 1845123ed1249..749dd1bfe60f9 100644
--- a/arch/um/sys-i386/syscalls.c
+++ b/arch/um/sys-i386/syscalls.c
@@ -61,21 +61,27 @@ long old_select(struct sel_arg_struct __user *arg)
 	return sys_select(a.n, a.inp, a.outp, a.exp, a.tvp);
 }
 
-/* The i386 version skips reading from %esi, the fourth argument. So we must do
- * this, too.
+/*
+ * The prototype on i386 is:
+ *
+ *     int clone(int flags, void * child_stack, int * parent_tidptr, struct user_desc * newtls, int * child_tidptr)
+ *
+ * and the "newtls" arg. on i386 is read by copy_thread directly from the
+ * register saved on the stack.
  */
 long sys_clone(unsigned long clone_flags, unsigned long newsp,
-	       int __user *parent_tid, int unused, int __user *child_tid)
+	       int __user *parent_tid, void *newtls, int __user *child_tid)
 {
 	long ret;
 
 	if (!newsp)
 		newsp = UPT_SP(&current->thread.regs.regs);
+
 	current->thread.forking = 1;
 	ret = do_fork(clone_flags, newsp, &current->thread.regs, 0, parent_tid,
 		      child_tid);
 	current->thread.forking = 0;
-	return(ret);
+	return ret;
 }
 
 /*