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Message-ID: <CABPqkBSupk4vizQ0t2CsgbNUtZLrQtKbSaLicO+hiXOfK52zQA@mail.gmail.com>
Date: Mon, 23 Apr 2012 12:15:25 +0200
From: Stephane Eranian <eranian@...gle.com>
To: Jiri Olsa <jolsa@...hat.com>
Cc: acme@...hat.com, a.p.zijlstra@...llo.nl, mingo@...e.hu,
paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
rostedt@...dmis.org, robert.richter@....com, fche@...hat.com,
linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
drepper@...il.com
Subject: Re: [PATCH 03/16] perf: Add ability to dump user regs
On Tue, Apr 17, 2012 at 1:17 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> Add new attr->user_regs bitmap that lets a user choose a set
> of user registers to dump to the sample. The layout of this
> bitmap is described in asm/perf_regs.h for archs that
> support register dump.
>
> The perf syscall will fail if attr->user_regs is non zero.
>
> The register value here are those 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).
>
> This is going to be useful to bring Dwarf CFI based stack unwinding
> on top of samples.
>
> TODO handle compat tasks
>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> ---
> include/linux/perf_event.h | 8 +++++
> kernel/events/core.c | 63 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 71 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index ddbb6a9..c63b807 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -272,6 +272,12 @@ struct perf_event_attr {
> __u64 config2; /* extension of config1 */
> };
> __u64 branch_sample_type; /* enum branch_sample_type */
> +
> + /*
> + * Arch specific mask that defines a set of user regs to dump on
> + * samples. See asm/perf_regs.h for details.
> + */
> + __u64 user_regs;
> };
>
Don't like the name of the field too much. You be more explicit.
Something like user_sample_regs.
> /*
> @@ -608,6 +614,7 @@ struct perf_guest_info_callbacks {
> #include <linux/atomic.h>
> #include <linux/sysfs.h>
> #include <asm/local.h>
> +#include <asm/perf_regs.h>
>
> #define PERF_MAX_STACK_DEPTH 255
>
> @@ -1130,6 +1137,7 @@ struct perf_sample_data {
> struct perf_callchain_entry *callchain;
> struct perf_raw_record *raw;
> struct perf_branch_stack *br_stack;
> + struct pt_regs *uregs;
> };
>
> static inline void perf_sample_data_init(struct perf_sample_data *data, u64 addr)
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index a6a9ec4..9f29fc3 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3751,6 +3751,37 @@ int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
> }
> EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
>
> +static void
> +perf_output_sample_regs(struct perf_output_handle *handle,
> + struct pt_regs *regs, u64 mask)
> +{
> + int i = 0;
> +
> + do {
> + u64 val;
> +
> + if (mask & 1) {
> + val = perf_reg_value(regs, i);
> + perf_output_put(handle, val);
> + }
> +
> + mask >>= 1;
> + i++;
> + } while (mask);
> +}
> +
> +static struct pt_regs *perf_sample_uregs(struct pt_regs *regs)
> +{
> + if (!user_mode(regs)) {
> + if (current->mm)
> + regs = task_pt_regs(current);
> + else
> + regs = NULL;
> + }
> +
> + return regs;
> +}
> +
You are assuming the user app is running the same ABI than that of the
kernel. That's not correct on X86 and possibly other architectures.
> static void __perf_event_header__init_id(struct perf_event_header *header,
> struct perf_sample_data *data,
> struct perf_event *event)
> @@ -4011,6 +4042,21 @@ void perf_output_sample(struct perf_output_handle *handle,
> perf_output_put(handle, nr);
> }
> }
> +
> + if (event->attr.user_regs) {
> + u64 id;
> +
> + /*
> + * If there are no regs to dump, notice it through a
> + * PERF_REGS_VERSION_NONE version.
> + */
> + id = data->uregs ? perf_reg_version() : PERF_REGS_VERSION_NONE;
> + perf_output_put(handle, id);
> +
> + if (id)
> + perf_output_sample_regs(handle, data->uregs,
> + event->attr.user_regs);
> + }
> }
>
> void perf_prepare_sample(struct perf_event_header *header,
> @@ -4062,6 +4108,16 @@ void perf_prepare_sample(struct perf_event_header *header,
> }
> header->size += size;
> }
> +
> + if (event->attr.user_regs) {
> + int size = sizeof(u64); /* the version size */
> +
> + data->uregs = perf_sample_uregs(regs);
> + if (data->uregs)
> + size += hweight64(event->attr.user_regs) * sizeof(u64);
> +
> + header->size += size;
> + }
> }
>
> static void perf_event_output(struct perf_event *event,
> @@ -6112,6 +6168,13 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
> attr->branch_sample_type = mask;
> }
> }
> +
> + /*
> + * Don't let throught invalid register mask (i.e. the architecture
> + * does not support register dump at all).
> + */
> + ret = perf_reg_validate(attr->user_regs);
> +
Again, how do you deal with 32-bit apps vs. 64-bit kernel?
> out:
> return ret;
>
> --
> 1.7.7.6
>
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