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SubjectRe: [PATCH 02/17] perf: Add ability to attach registers dump to sample
On Wed, May 02, 2012 at 01:37:03PM +0200, Jiri Olsa wrote:
> Introducing new sample_type bit PERF_SAMPLE_REGS. Once set,
> the sample_regs value determines the kind of registers going
> to be attached to the sample.
>
> Currently only user level registers are supported, specified by
> PERF_SAMPLE_REGS_USER sample_regs value. Meaning the register
> values of the user space context as it was before the user entered
> the kernel for whatever reason (syscall, irq, exception, or a PMI
> happening in userspace).
>
> When PERF_SAMPLE_REGS and PERF_SAMPLE_REGS_USER are set, the
> sample_regs_user bitmap lets a user choose a set of registers
> to dump for the sample. The layout of this bitmap is described
> in asm/perf_regs.h for archs that support register dump.
>
> This is going to be useful to bring Dwarf CFI based stack
> unwinding on top of samples.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> ---
> include/linux/perf_event.h | 25 ++++++++++-
> kernel/events/core.c | 98 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 121 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index ddbb6a9..6a8c974 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -130,8 +130,9 @@ enum perf_event_sample_format {
> PERF_SAMPLE_STREAM_ID = 1U << 9,
> PERF_SAMPLE_RAW = 1U << 10,
> PERF_SAMPLE_BRANCH_STACK = 1U << 11,
> + PERF_SAMPLE_REGS = 1U << 12,

Given that we have to provide a reg mask anyway, is this sample type
necessary? Zeroed mask means we don't want to record regs.

>
> - PERF_SAMPLE_MAX = 1U << 12, /* non-ABI */
> + PERF_SAMPLE_MAX = 1U << 13, /* non-ABI */
> };
>
> /*
> @@ -163,6 +164,15 @@ enum perf_branch_sample_type {
> PERF_SAMPLE_BRANCH_HV)
>
> /*
> + * Values for sample_regs when PERF_SAMPLE_REGS is set.
> + * Defines register set to be attached to the sample.
> + */
> +enum perf_sample_regs {
> + PERF_SAMPLE_REGS_USER = 1U << 0, /* user registers */
> + PERF_SAMPLE_REGS_MAX = 1U << 1, /* non-ABI */
> +};

If this is an enum, we won't be able to record multiple types of regs
(eg: user regs and event live regs) in a single sample.

> +
> +/*
> * The format of the data returned by read() on a perf event fd,
> * as specified by attr.read_format:
> *
> @@ -271,7 +281,16 @@ struct perf_event_attr {
> __u64 bp_len;
> __u64 config2; /* extension of config1 */
> };
> - __u64 branch_sample_type; /* enum branch_sample_type */
> + __u64 branch_sample_type; /* enum perf_branch_sample_type */
> +
> + __u64 sample_regs; /* enum perf_sample_regs */
> +
> + /*
> + * Arch specific mask for PERF_SAMPLE_REGS_USER setup.
> + * Defines set of user regs to dump on samples.
> + * See asm/perf_regs.h for details.
> + */
> + __u64 sample_regs_user;

We need to sort that out now. How do we handle normal/compat regs?
Do we want sample_regs_user_64 and sample_regs_user_32? Or can we
make it possible with a single field like above? Should we
expect more modes than just a simple native and compat? I don't
know much the world outside x86.

Would be nice to have the opinion of other people on this. Ingo, Peter, others?

Thanks.


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