[PATCH v4] microblaze: Fix clone syscall

[Michal Simek]

Fix inadvertent breakage in the clone syscall ABI for Microblaze
that was introduced in this patch:
"microblaze: switch to generic fork/vfork/clone"
(sha1: f3268edbe6fe0ce56e62c6d6b14640aeb04864b7)

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@xxxxxxxxxx>

---
Changes in v4:
 - use ifdef in syscalls.h instead of simple if (it is breaking  make ARCH=x86_64 allnoconfig)
 - Compilation passed by kbuild robot

Changes in v3:
 - Change patch description based on Rich comments.

Changes in v2:
 - Add information about the first broken patch - Suggested by Andrew

 arch/Kconfig             | 6 ++++++
 arch/microblaze/Kconfig  | 2 +-
 include/linux/syscalls.h | 5 +++++
 kernel/fork.c            | 6 ++++++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8d2ae24..1feb169 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 d22a4ec..4fab522 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
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 4147d70..84662ec 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -802,9 +802,14 @@ asmlinkage long sys_vfork(void);
 asmlinkage long sys_clone(unsigned long, unsigned long, int __user *, int,
 	       int __user *);
 #else
+#ifdef CONFIG_CLONE_BACKWARDS3
+asmlinkage long sys_clone(unsigned long, unsigned long, int, int __user *,
+			  int __user *, int);
+#else
 asmlinkage long sys_clone(unsigned long, unsigned long, int __user *,
 	       int __user *, int);
 #endif
+#endif

 asmlinkage long sys_execve(const char __user *filename,
 		const char __user *const __user *argv,
diff --git a/kernel/fork.c b/kernel/fork.c
index 403d2bb..e23bb19 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1679,6 +1679,12 @@ SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
 		 int __user *, parent_tidptr,
 		 int __user *, child_tidptr,
 		 int, tls_val)
+#elif defined(CONFIG_CLONE_BACKWARDS3)
+SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
+		int, stack_size,
+		int __user *, parent_tidptr,
+		int __user *, child_tidptr,
+		int, tls_val)
 #else
 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 		 int __user *, parent_tidptr,
--
1.8.2.3

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