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authorHeiko Carstens <heiko.carstens@de.ibm.com>2015-01-29 14:10:22 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2015-01-29 16:33:34 +0100
commitd5caa4dbf9bd2ad8cd7f6be0ca76722be947182b (patch)
tree6d58cdd140333e17c881667e9691b17f7dcd6e4d /arch/s390
parent5c6497c50f8d809eac6d01512c291a1f67382abd (diff)
s390/jump label: use different nop instruction
Use a brcl 0,2 instruction for jump label nops during compile time, so we don't mix up the different nops during mcount/hotpatch call site detection. The initial jump label code instruction replacement will exchange these instructions with either a branch or a brcl 0,0 instruction. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/include/asm/jump_label.h7
-rw-r--r--arch/s390/kernel/jump_label.c19
2 files changed, 19 insertions, 7 deletions
diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
index 346b1c85ffb4..58642fd29c87 100644
--- a/arch/s390/include/asm/jump_label.h
+++ b/arch/s390/include/asm/jump_label.h
@@ -4,6 +4,7 @@
#include <linux/types.h>
#define JUMP_LABEL_NOP_SIZE 6
+#define JUMP_LABEL_NOP_OFFSET 2
#ifdef CONFIG_64BIT
#define ASM_PTR ".quad"
@@ -13,9 +14,13 @@
#define ASM_ALIGN ".balign 4"
#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.
+ */
static __always_inline bool arch_static_branch(struct static_key *key)
{
- asm_volatile_goto("0: brcl 0,0\n"
+ asm_volatile_goto("0: brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
".pushsection __jump_table, \"aw\"\n"
ASM_ALIGN "\n"
ASM_PTR " 0b, %l[label], %0\n"
diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
index 25aef40584f7..cb2d51e779df 100644
--- a/arch/s390/kernel/jump_label.c
+++ b/arch/s390/kernel/jump_label.c
@@ -49,6 +49,11 @@ static void jump_label_bug(struct jump_entry *entry, struct insn *insn)
panic("Corrupted kernel text");
}
+static struct insn orignop = {
+ .opcode = 0xc004,
+ .offset = JUMP_LABEL_NOP_OFFSET >> 1,
+};
+
static void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
int init)
@@ -59,14 +64,16 @@ static void __jump_label_transform(struct jump_entry *entry,
jump_label_make_nop(entry, &old);
jump_label_make_branch(entry, &new);
} else {
- if (init)
- jump_label_make_nop(entry, &old);
- else
- jump_label_make_branch(entry, &old);
+ jump_label_make_branch(entry, &old);
jump_label_make_nop(entry, &new);
}
- if (memcmp((void *)entry->code, &old, sizeof(old)))
- jump_label_bug(entry, &old);
+ if (init) {
+ if (memcmp((void *)entry->code, &orignop, sizeof(orignop)))
+ jump_label_bug(entry, &old);
+ } else {
+ if (memcmp((void *)entry->code, &old, sizeof(old)))
+ jump_label_bug(entry, &old);
+ }
probe_kernel_write((void *)entry->code, &new, sizeof(new));
}