x86: don't clobber r8 nor use rcx.

There's really no reason to clobber r8 or pass the address in rcx.
We can safely use only two registers (which we already have to touch anyway)
to do the job.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 22 insertions, 23 deletions

diff --git a/arch/x86/lib/getuser_64.S b/arch/x86/lib/getuser_64.S
index 5448876261f8..2b003d313480 100644
--- a/arch/x86/lib/getuser_64.S
+++ b/arch/x86/lib/getuser_64.S
@@ -36,10 +36,10 @@
         .text
 ENTRY(__get_user_1)
         CFI_STARTPROC
-        GET_THREAD_INFO(%r8)
-        cmpq threadinfo_addr_limit(%r8),%rcx
+        GET_THREAD_INFO(%rdx)
+        cmpq threadinfo_addr_limit(%rdx),%rax
         jae bad_get_user
-1:      movzb (%rcx),%edx
+1:      movzb (%rax),%edx
         xorl %eax,%eax
         ret
         CFI_ENDPROC
@@ -47,48 +47,48 @@ ENDPROC(__get_user_1)
 
 ENTRY(__get_user_2)
         CFI_STARTPROC
-        GET_THREAD_INFO(%r8)
-        addq $1,%rcx
+        GET_THREAD_INFO(%rdx)
+        addq $1,%rax
         jc 20f
-        cmpq threadinfo_addr_limit(%r8),%rcx
+        cmpq threadinfo_addr_limit(%rdx),%rax
         jae 20f
-        decq   %rcx
-2:      movzwl (%rcx),%edx
+        decq   %rax
+2:      movzwl (%rax),%edx
         xorl %eax,%eax
         ret
-20:     decq    %rcx
+20:     decq    %rax
         jmp     bad_get_user
         CFI_ENDPROC
 ENDPROC(__get_user_2)
 
 ENTRY(__get_user_4)
         CFI_STARTPROC
-        GET_THREAD_INFO(%r8)
-        addq $3,%rcx
+        GET_THREAD_INFO(%rdx)
+        addq $3,%rax
         jc 30f
-        cmpq threadinfo_addr_limit(%r8),%rcx
+        cmpq threadinfo_addr_limit(%rdx),%rax
         jae 30f
-        subq $3,%rcx
-3:      movl (%rcx),%edx
+        subq $3,%rax
+3:      movl (%rax),%edx
         xorl %eax,%eax
         ret
-30:     subq $3,%rcx
+30:     subq $3,%rax
         jmp bad_get_user
         CFI_ENDPROC
 ENDPROC(__get_user_4)
 
 ENTRY(__get_user_8)
         CFI_STARTPROC
-        GET_THREAD_INFO(%r8)
-        addq $7,%rcx
+        GET_THREAD_INFO(%rdx)
+        addq $7,%rax
         jc 40f
-        cmpq threadinfo_addr_limit(%r8),%rcx
+        cmpq threadinfo_addr_limit(%rdx),%rax
         jae     40f
-        subq    $7,%rcx
-4:      movq (%rcx),%rdx
+        subq    $7,%rax
+4:      movq (%rax),%rdx
         xorl %eax,%eax
         ret
-40:     subq $7,%rcx
+40:     subq $7,%rax
         jmp bad_get_user
         CFI_ENDPROC
 ENDPROC(__get_user_8)
diff --git a/include/asm-x86/uaccess_64.h b/include/asm-x86/uaccess_64.h
index b8a2f4339903..a2d49078e19c 100644
--- a/include/asm-x86/uaccess_64.h
+++ b/include/asm-x86/uaccess_64.h
@@ -90,8 +90,7 @@ extern int fixup_exception(struct pt_regs *regs);
 #define __get_user_x(size, ret, x, ptr)               \
         asm volatile("call __get_user_" #size         \
                      : "=a" (ret),"=d" (x)            \
-                     : "c" (ptr)                      \
-                     : "r8")
+                     : "0" (ptr))                     \
 
 /* Careful: we have to cast the result to the type of the pointer
  * for sign reasons */