When the tool runs with compat mode on Arm platform, the kernel is in 64-bit mode and user space is in 32-bit mode; the user space can use instructions "ldrd" and "strd" for 64-bit value atomicity.
This patch adds compat_auxtrace_mmap__{read_head|write_tail} for arm building, it uses "ldrd" and "strd" instructions to ensure accessing atomicity for aux head and tail. The file arch/arm/util/auxtrace.c is built for arm and arm64 building, these two functions are not needed for arm64, so check the compiler macro "__arm__" to only include them for arm building.
Signed-off-by: Leo Yan leo.yan@linaro.org --- tools/perf/arch/arm/util/auxtrace.c | 32 +++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
diff --git a/tools/perf/arch/arm/util/auxtrace.c b/tools/perf/arch/arm/util/auxtrace.c index b187bddbd01a..c7c7ec0812d5 100644 --- a/tools/perf/arch/arm/util/auxtrace.c +++ b/tools/perf/arch/arm/util/auxtrace.c @@ -107,3 +107,35 @@ struct auxtrace_record *err = 0; return NULL; } + +#if defined(__arm__) +u64 compat_auxtrace_mmap__read_head(struct auxtrace_mmap *mm) +{ + struct perf_event_mmap_page *pc = mm->userpg; + u64 result; + + __asm__ __volatile__( +" ldrd %0, %H0, [%1]" + : "=&r" (result) + : "r" (&pc->aux_head), "Qo" (pc->aux_head) + ); + + return result; +} + +int compat_auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail) +{ + struct perf_event_mmap_page *pc = mm->userpg; + + /* Ensure all reads are done before we write the tail out */ + smp_mb(); + + __asm__ __volatile__( +" strd %2, %H2, [%1]" + : "=Qo" (pc->aux_tail) + : "r" (&pc->aux_tail), "r" (tail) + ); + + return 0; +} +#endif