Skip to content

Commit

Permalink
i#3956 arm locks: Use release-acquire atomics for ARM (#4262)
Browse files Browse the repository at this point in the history 
Adds a "dmb ish" barrier prior to the "ldrex..strex" loops in the
atomics used to implement mutexes and other operations on 32-bit ARM
where we need release-acquire semantics.

Issue: #3956
  • Loading branch information
@derekbruening
derekbruening authored Apr 20, 2020
1 parent 4f9b460 commit a072799
Showing 1 changed file with 12 additions and 6 deletions.
18 changes: 12 additions & 6 deletions core/arch/arch_exports.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -857,7 +857,8 @@ atomic_dec_becomes_zero(volatile int *var)
*/
/* FIXME i#1551: should we allow infinite loops for those ATOMIC ops */
# define ATOMIC_INC_suffix(suffix, var) \
__asm__ __volatile__("1: ldrex" suffix " r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"1: ldrex" suffix " r2, %0 \n\t" \
" add" suffix " r2, r2, #1 \n\t" \
" strex" suffix " r3, r2, %0 \n\t" \
" cmp r3, #0 \n\t" \
Expand All @@ -870,7 +871,8 @@ atomic_dec_becomes_zero(volatile int *var)
# define ATOMIC_INC_int64(var) ATOMIC_INC_suffix("d", var)
# define ATOMIC_INC(type, var) ATOMIC_INC_##type(var)
# define ATOMIC_DEC_suffix(suffix, var) \
__asm__ __volatile__("1: ldrex" suffix " r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"1: ldrex" suffix " r2, %0 \n\t" \
" sub" suffix " r2, r2, #1 \n\t" \
" strex" suffix " r3, r2, %0 \n\t" \
" cmp r3, #0 \n\t" \
Expand All @@ -883,7 +885,8 @@ atomic_dec_becomes_zero(volatile int *var)
# define ATOMIC_DEC_int64(var) ATOMIC_DEC_suffix("d", var)
# define ATOMIC_DEC(type, var) ATOMIC_DEC_##type(var)
# define ATOMIC_ADD_suffix(suffix, var, value) \
__asm__ __volatile__("1: ldrex" suffix " r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"1: ldrex" suffix " r2, %0 \n\t" \
" add" suffix " r2, r2, %1 \n\t" \
" strex" suffix " r3, r2, %0 \n\t" \
" cmp r3, #0 \n\t" \
Expand All @@ -897,7 +900,8 @@ atomic_dec_becomes_zero(volatile int *var)
# define ATOMIC_ADD(type, var, val) ATOMIC_ADD_##type(var, val)
/* Not safe for general use, just for atomic_add_exchange(), undefed below */
# define ATOMIC_ADD_EXCHANGE_suffix(suffix, var, value, result) \
__asm__ __volatile__("1: ldrex" suffix " r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"1: ldrex" suffix " r2, %0 \n\t" \
" add" suffix " r2, r2, %2 \n\t" \
" strex" suffix " r3, r2, %0 \n\t" \
" cmp r3, #0 \n\t" \
Expand All @@ -912,7 +916,8 @@ atomic_dec_becomes_zero(volatile int *var)
# define ATOMIC_ADD_EXCHANGE_int64(var, val, res) \
ATOMIC_ADD_EXCHANGE_suffix("d", var, val, res)
# define ATOMIC_COMPARE_EXCHANGE_suffix(suffix, var, compare, exchange) \
__asm__ __volatile__("2: ldrex" suffix " r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"2: ldrex" suffix " r2, %0 \n\t" \
" cmp" suffix " r2, %1 \n\t" \
" bne 1f \n\t" \
" strex" suffix " r3, %2, %0 \n\t" \
Expand All @@ -928,7 +933,8 @@ atomic_dec_becomes_zero(volatile int *var)
# define ATOMIC_COMPARE_EXCHANGE_int64(var, compare, exchange) \
ATOMIC_COMPARE_EXCHANGE_suffix("d", var, compare, exchange)
# define ATOMIC_EXCHANGE(var, newval, result) \
__asm__ __volatile__("1: ldrex r2, %0 \n\t" \
__asm__ __volatile__(" dmb ish \n\t" \
"1: ldrex r2, %0 \n\t" \
" strex r3, %2, %0 \n\t" \
" cmp r3, #0 \n\t" \
" bne 1b \n\t" \
Expand Down

0 comments on commit a072799

Please sign in to comment.