microblaze: fix clone syscall

Fix inadvertent breakage in the clone syscall ABI for Microblaze that
was introduced in commit f3268edbe6fe ("microblaze: switch to generic
fork/vfork/clone").

The Microblaze syscall ABI for clone takes the parent tid address in the
4th argument; the third argument slot is used for the stack size.  The
incorrectly-used CLONE_BACKWARDS type assigned parent tid to the 3rd
slot.

This commit restores the original ABI so that existing userspace libc
code will work correctly.

All kernel versions from v3.8-rc1 were affected.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 7 insertions, 1 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 8d2ae24b9f4a..1feb169274fe 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -407,6 +407,12 @@ config CLONE_BACKWARDS2
         help
           Architecture has the first two arguments of clone(2) swapped.
 
+config CLONE_BACKWARDS3
+        bool
+        help
+          Architecture has tls passed as the 3rd argument of clone(2),
+          not the 5th one.
+
 config ODD_RT_SIGACTION
         bool
         help
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index d22a4ecffff4..4fab52294d98 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -28,7 +28,7 @@ config MICROBLAZE
         select GENERIC_CLOCKEVENTS
         select GENERIC_IDLE_POLL_SETUP
         select MODULES_USE_ELF_RELA
-        select CLONE_BACKWARDS
+        select CLONE_BACKWARDS3
 
 config SWAP
         def_bool n