diff options
Diffstat (limited to 'arch/arm')
| -rw-r--r-- | arch/arm/kernel/entry-ftrace.S | 2 | ||||
| -rw-r--r-- | arch/arm/kernel/ftrace.c | 15 |
2 files changed, 14 insertions, 3 deletions
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index f4886fb6e9ba..dca12a09322a 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -27,7 +27,7 @@ * allows it to be clobbered in subroutines and doesn't use it to hold * parameters.) * - * When using dynamic ftrace, we patch out the mcount call by a "pop {lr}" + * When using dynamic ftrace, we patch out the mcount call by a "add sp, #4" * instead of the __gnu_mcount_nc call (see arch/arm/kernel/ftrace.c). */ diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c index a006585e1c09..811cadf7eefc 100644 --- a/arch/arm/kernel/ftrace.c +++ b/arch/arm/kernel/ftrace.c @@ -24,10 +24,21 @@ #include <asm/set_memory.h> #include <asm/patch.h> +/* + * The compiler emitted profiling hook consists of + * + * PUSH {LR} + * BL __gnu_mcount_nc + * + * To turn this combined sequence into a NOP, we need to restore the value of + * SP before the PUSH. Let's use an ADD rather than a POP into LR, as LR is not + * modified anyway, and reloading LR from memory is highly likely to be less + * efficient. + */ #ifdef CONFIG_THUMB2_KERNEL -#define NOP 0xf85deb04 /* pop.w {lr} */ +#define NOP 0xf10d0d04 /* add.w sp, sp, #4 */ #else -#define NOP 0xe8bd4000 /* pop {lr} */ +#define NOP 0xe28dd004 /* add sp, sp, #4 */ #endif #ifdef CONFIG_DYNAMIC_FTRACE |