[PATCH] s390/jump_label: Use "jdd" constraint on gcc9

[Ilya Leoshkevich <iii@linux.ibm.com>]

> Ah okay, I didn't realize there was more needed, I was just looking at
> the clean cherry-pick. I'm not sure how to do the backport, if you
> give me the patch I can verify.

Please find the cherry-picked 146448524bdd below.

I also had to cherry-pick 159491f3b509 to fix an unrelated compilation
error and make the build fully work.

Best regards,
Ilya

----

[heiko.carstens@de.ibm.com]:
-----
Laura Abbott reported that the kernel doesn't build anymore with gcc 9,
due to the "X" constraint. Ilya provided the gcc 9 patch "S/390:
Introduce jdd constraint" which introduces the new "jdd" constraint
which fixes this.
-----

The support for section anchors on S/390 introduced in gcc9 has changed
the behavior of "X" constraint, which can now produce register
references. Since existing constraints, in particular, "i", do not fit
the intended use case on S/390, the new machine-specific "jdd"
constraint was introduced. This patch makes jump labels use "jdd"
constraint when building with gcc9.

Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/include/asm/jump_label.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
index 40f651292aa7..9c7dc970e966 100644
--- a/arch/s390/include/asm/jump_label.h
+++ b/arch/s390/include/asm/jump_label.h
@@ -10,6 +10,12 @@
 #define JUMP_LABEL_NOP_SIZE 6
 #define JUMP_LABEL_NOP_OFFSET 2
 
+#if __GNUC__ < 9
+#define JUMP_LABEL_STATIC_KEY_CONSTRAINT "X"
+#else
+#define JUMP_LABEL_STATIC_KEY_CONSTRAINT "jdd"
+#endif
+
 /*
  * We use a brcl 0,2 instruction for jump labels at compile time so it
  * can be easily distinguished from a hotpatch generated instruction.
@@ -19,9 +25,9 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 	asm_volatile_goto("0:	brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
 		".pushsection __jump_table, \"aw\"\n"
 		".balign 8\n"
-		".quad 0b, %l[label], %0\n"
+		".quad 0b, %l[label], %0+%1\n"
 		".popsection\n"
-		: : "X" (&((char *)key)[branch]) : : label);
+		: : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
 
 	return false;
 label:
@@ -33,9 +39,9 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 	asm_volatile_goto("0:	brcl 15, %l[label]\n"
 		".pushsection __jump_table, \"aw\"\n"
 		".balign 8\n"
-		".quad 0b, %l[label], %0\n"
+		".quad 0b, %l[label], %0+%1\n"
 		".popsection\n"
-		: : "X" (&((char *)key)[branch]) : : label);
+		: : JUMP_LABEL_STATIC_KEY_CONSTRAINT (key), "i" (branch) : : label);
 
 	return false;
 label:
-- 
2.21.0