s390/current: Implement current with inline assembly

Implement current with an inline assembly, which makes use of the
ALTERNATIVE macro, to read current from lowcore. Provide an alternative
instruction with a different offset in case lowcore is relocated.

This replaces sequences of two instructions with one instruction.

Before:
 100076:       a5 1e 00 00             llilh   %r1,0
 10007a:       e3 40 13 40 00 04       lg      %r4,832(%r1)

After:
 100076:       e3 10 03 40 00 04       lg      %r1,832

Kernel image size change:
add/remove: 3/17 grow/shrink: 166/2204 up/down: 7122/-24594 (-17472)

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/include/asm/current.h b/arch/s390/include/asm/current.h
index d03a922c641e2247f072f295b19eb9f0713dd0cb..f9529f7cf62cf51a469d796097c808bbbd5d681c 100644 (file)
--- a/arch/s390/include/asm/current.h
+++ b/arch/s390/include/asm/current.h
@@ -11,9 +11,25 @@
 #define _S390_CURRENT_H
 
 #include <asm/lowcore.h>
+#include <asm/machine.h>
 
 struct task_struct;
 
-#define current ((struct task_struct *const)get_lowcore()->current_task)
+static __always_inline struct task_struct *get_current(void)
+{
+       unsigned long ptr, lc_current;
+
+       lc_current = offsetof(struct lowcore, current_task);
+       asm_inline(
+               ALTERNATIVE("   lg      %[ptr],%[offzero](%%r0)\n",
+                           "   lg      %[ptr],%[offalt](%%r0)\n",
+                           ALT_FEATURE(MFEATURE_LOWCORE))
+               : [ptr] "=d" (ptr)
+               : [offzero] "i" (lc_current),
+                 [offalt] "i" (lc_current + LOWCORE_ALT_ADDRESS));
+       return (struct task_struct *)ptr;
+}
+
+#define current get_current()
 
 #endif /* !(_S390_CURRENT_H) */