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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>
This commit is contained in:
Heiko Carstens 2015-01-29 14:10:22 +01:00 committed by Martin Schwidefsky
parent 5c6497c50f
commit d5caa4dbf9
2 changed files with 19 additions and 7 deletions
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7
arch/s390/include/asm/jump_label.h
View File

@ -4,6 +4,7 @@
#include <linux/types.h> #include <linux/types.h>
#define JUMP_LABEL_NOP_SIZE 6 #define JUMP_LABEL_NOP_SIZE 6
#define JUMP_LABEL_NOP_OFFSET 2
#ifdef CONFIG_64BIT #ifdef CONFIG_64BIT
#define ASM_PTR ".quad" #define ASM_PTR ".quad"
@ -13,9 +14,13 @@
#define ASM_ALIGN ".balign 4" #define ASM_ALIGN ".balign 4"
#endif #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) 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" ".pushsection __jump_table, \"aw\"\n"
ASM_ALIGN "\n" ASM_ALIGN "\n"
ASM_PTR " 0b, %l[label], %0\n" ASM_PTR " 0b, %l[label], %0\n"

19
arch/s390/kernel/jump_label.c
View File

@ -49,6 +49,11 @@ static void jump_label_bug(struct jump_entry *entry, struct insn *insn)
panic("Corrupted kernel text"); 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, static void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type, enum jump_label_type type,
int init) int init)
@ -59,14 +64,16 @@ static void __jump_label_transform(struct jump_entry *entry,
jump_label_make_nop(entry, &old); jump_label_make_nop(entry, &old);
jump_label_make_branch(entry, &new); jump_label_make_branch(entry, &new);
} else { } else {
if (init) jump_label_make_branch(entry, &old);
jump_label_make_nop(entry, &old);
else
jump_label_make_branch(entry, &old);
jump_label_make_nop(entry, &new); jump_label_make_nop(entry, &new);
} }
if (memcmp((void *)entry->code, &old, sizeof(old))) if (init) {
jump_label_bug(entry, &old); 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)); probe_kernel_write((void *)entry->code, &new, sizeof(new));
} }