diff options
| -rw-r--r-- | arch/arm/include/asm/spinlock.h | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h index da1af5240159..fdd3820edff8 100644 --- a/arch/arm/include/asm/spinlock.h +++ b/arch/arm/include/asm/spinlock.h @@ -18,7 +18,23 @@ #ifdef CONFIG_THUMB2_KERNEL #define SEV ALT_SMP("sev.w", "nop.w") -#define WFE(cond) ALT_SMP("wfe" cond ".w", "nop.w") +/* + * For Thumb-2, special care is needed to ensure that the conditional WFE + * instruction really does assemble to exactly 4 bytes (as required by + * the SMP_ON_UP fixup code). By itself "wfene" might cause the + * assembler to insert a extra (16-bit) IT instruction, depending on the + * presence or absence of neighbouring conditional instructions. + * + * To avoid this unpredictableness, an approprite IT is inserted explicitly: + * the assembler won't change IT instructions which are explicitly present + * in the input. + */ +#define WFE(cond) ALT_SMP( \ + "it " cond "\n\t" \ + "wfe" cond ".n", \ + \ + "nop.w" \ +) #else #define SEV ALT_SMP("sev", "nop") #define WFE(cond) ALT_SMP("wfe" cond, "nop") |