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SubjectRe: [PATCH v2 4/4] perf tools: arm64: Add support for VG register
On Tue, May 17, 2022 at 11:20:05AM +0100, James Clark wrote:
> Add the name of the VG register so it can be used in --user-regs
>
> The event will fail to open if the register is requested but not
> available so only add it to the mask if the kernel supports sve and also
> if it supports that specific register.
>
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
> tools/perf/arch/arm64/util/perf_regs.c | 34 ++++++++++++++++++++++++++
> tools/perf/util/perf_regs.c | 2 ++
> 2 files changed, 36 insertions(+)
>
> diff --git a/tools/perf/arch/arm64/util/perf_regs.c b/tools/perf/arch/arm64/util/perf_regs.c
> index 476b037eea1c..c0a921512a90 100644
> --- a/tools/perf/arch/arm64/util/perf_regs.c
> +++ b/tools/perf/arch/arm64/util/perf_regs.c
> @@ -2,9 +2,11 @@
> #include <errno.h>
> #include <regex.h>
> #include <string.h>
> +#include <sys/auxv.h>
> #include <linux/kernel.h>
> #include <linux/zalloc.h>
>
> +#include "../../../perf-sys.h"
> #include "../../../util/debug.h"
> #include "../../../util/event.h"
> #include "../../../util/perf_regs.h"
> @@ -43,6 +45,7 @@ const struct sample_reg sample_reg_masks[] = {
> SMPL_REG(lr, PERF_REG_ARM64_LR),
> SMPL_REG(sp, PERF_REG_ARM64_SP),
> SMPL_REG(pc, PERF_REG_ARM64_PC),
> + SMPL_REG(vg, PERF_REG_ARM64_VG),
> SMPL_REG_END
> };
>
> @@ -131,3 +134,34 @@ int arch_sdt_arg_parse_op(char *old_op, char **new_op)
>
> return SDT_ARG_VALID;
> }
> +
> +uint64_t arch__user_reg_mask(void)
> +{
> + struct perf_event_attr attr = {
> + .type = PERF_TYPE_HARDWARE,
> + .config = PERF_COUNT_HW_CPU_CYCLES,
> + .sample_type = PERF_SAMPLE_REGS_USER,
> + .disabled = 1,
> + .exclude_kernel = 1,
> + .sample_period = 1,
> + .sample_regs_user = PERF_REGS_MASK
> + };
> + int fd;
> +
> + if (getauxval(AT_HWCAP) & HWCAP_SVE)
> + attr.sample_regs_user |= SMPL_REG_MASK(PERF_REG_ARM64_VG);
> +
> + /*
> + * Check if the pmu supports perf extended regs, before
> + * returning the register mask to sample.
> + */
> + if (attr.sample_regs_user != PERF_REGS_MASK) {
> + event_attr_init(&attr);
> + fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
> + if (fd != -1) {
> + close(fd);
> + return attr.sample_regs_user;
> + }
> + }

Just curious, since we can know SVE is supported from reading
auxiliary value, can we directly return the register mask as below?

PERF_REGS_MASK | SMPL_REG_MASK(PERF_REG_ARM64_VG);

Except this question, this patch looks good to me.

Thanks,
Leo

> + return PERF_REGS_MASK;
> +}
> diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c
> index a982e40ee5a9..872dd3d38782 100644
> --- a/tools/perf/util/perf_regs.c
> +++ b/tools/perf/util/perf_regs.c
> @@ -103,6 +103,8 @@ static const char *__perf_reg_name_arm64(int id)
> return "lr";
> case PERF_REG_ARM64_PC:
> return "pc";
> + case PERF_REG_ARM64_VG:
> + return "vg";
> default:
> return NULL;
> }
> --
> 2.28.0
>

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