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    Subject[PATCH 04/17] perf: Add ability to attach user stack dump to sample
    Date
    Introducing new sample_type bit PERF_SAMPLE_STACK. Once set,
    the sample_stack value determines the stack which is going
    to be attached.

    Currently only user level stack is supported, specified by
    PERF_SAMPLE_STACK_USER bit in sample_stack value. When set,
    the sample_stack_user value determines the size of the
    stack dump.

    Beeing able to dump parts of the user stack, starting from the
    stack pointer, will be useful to make a post mortem dwarf CFI
    based stack unwinding.

    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Signed-off-by: Jiri Olsa <jolsa@redhat.com>
    ---
    include/linux/perf_event.h | 20 ++++++++-
    kernel/events/core.c | 103 ++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 122 insertions(+), 1 deletions(-)

    diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    index dcda0f16..2e5f486 100644
    --- a/include/linux/perf_event.h
    +++ b/include/linux/perf_event.h
    @@ -131,8 +131,9 @@ enum perf_event_sample_format {
    PERF_SAMPLE_RAW = 1U << 10,
    PERF_SAMPLE_BRANCH_STACK = 1U << 11,
    PERF_SAMPLE_REGS = 1U << 12,
    + PERF_SAMPLE_STACK = 1U << 13,

    - PERF_SAMPLE_MAX = 1U << 13, /* non-ABI */
    + PERF_SAMPLE_MAX = 1U << 14, /* non-ABI */
    };

    /*
    @@ -173,6 +174,15 @@ enum perf_sample_regs {
    };

    /*
    + * Values for sample_stack when PERF_SAMPLE_STACK is set.
    + * Defines stack dump to be attached to the sample.
    + */
    +enum perf_sample_stack {
    + PERF_SAMPLE_STACK_USER = 1U << 0, /* user stack */
    + PERF_SAMPLE_STACK_MAX = 1U << 1, /* non-ABI */
    +};
    +
    +/*
    * The format of the data returned by read() on a perf event fd,
    * as specified by attr.read_format:
    *
    @@ -291,6 +301,14 @@ struct perf_event_attr {
    * See asm/perf_regs.h for details.
    */
    __u64 sample_regs_user;
    +
    + __u64 sample_stack; /* enum perf_sample_stack */
    +
    + /*
    + * Defines size of the user stack to dump on samples,
    + * for sample_stack PERF_SAMPLE_STACK_USER settings.
    + */
    + __u64 sample_stack_user;
    };

    /*
    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index dd99718..b9206c4 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -3770,6 +3770,45 @@ perf_output_sample_regs(struct perf_output_handle *handle,
    } while (mask);
    }

    +static void
    +perf_output_sample_ustack(struct perf_output_handle *handle, u64 dump_size,
    + struct pt_regs *regs)
    +{
    + u64 size;
    +
    + /* Case of a kernel thread, nothing to dump */
    + if (!regs) {
    + size = 0;
    + perf_output_put(handle, size);
    + } else {
    + unsigned long sp;
    + unsigned int rem;
    + u64 dyn_size;
    +
    + /*
    + * Static size: we always dump the size
    + * requested by the user because most of the
    + * time, the top of the user stack is not
    + * paged out.
    + */
    + size = round_up(dump_size, sizeof(u64));
    + perf_output_put(handle, size);
    +
    + sp = user_stack_pointer(regs);
    + rem = __output_copy_user(handle, (void *)sp, size);
    + dyn_size = size - rem;
    +
    + /* What couldn't be dumped is zero padded */
    + while (rem--) {
    + char zero = 0;
    + perf_output_put(handle, zero);
    + }
    +
    + /* Dynamic size: whole dump - padding */
    + perf_output_put(handle, dyn_size);
    + }
    +}
    +
    static struct pt_regs *perf_sample_regs_user(struct pt_regs *regs)
    {
    if (!user_mode(regs)) {
    @@ -4066,6 +4105,17 @@ void perf_output_sample(struct perf_output_handle *handle,
    }
    }
    }
    +
    + if (sample_type & PERF_SAMPLE_STACK) {
    + u64 mode = event->attr.sample_stack;
    +
    + if (mode & PERF_SAMPLE_STACK_USER) {
    + u64 dump_size = event->attr.sample_stack_user;
    +
    + perf_output_sample_ustack(handle, dump_size,
    + data->regs_user);
    + }
    + }
    }

    void perf_prepare_sample(struct perf_event_header *header,
    @@ -4135,6 +4185,39 @@ void perf_prepare_sample(struct perf_event_header *header,

    header->size += size;
    }
    +
    + if (sample_type & PERF_SAMPLE_STACK) {
    + u64 mode = event->attr.sample_stack;
    + int size = 0;
    +
    + if (mode & PERF_SAMPLE_STACK_USER) {
    + if (!data->regs_user)
    + data->regs_user = perf_sample_regs_user(regs);
    +
    + /*
    + * A first field that tells the _static_ size of the
    + * dump. 0 if there is nothing to dump (ie: we are in
    + * a kernel thread) otherwise the requested size.
    + */
    + size += sizeof(u64);
    +
    + /*
    + * If there is something to dump, add space for the
    + * dump itself and for the field that tells the
    + * dynamic size, which is how many have been actually
    + * dumped. What couldn't be dumped will be zero-padded.
    + */
    + if (data->regs_user) {
    + u64 user_size = event->attr.sample_stack_user;
    +
    + user_size = round_up(user_size, sizeof(u64));
    + size += user_size;
    + size += sizeof(u64);
    + }
    + }
    +
    + header->size += size;
    + }
    }

    static void perf_event_output(struct perf_event *event,
    @@ -6210,6 +6293,26 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
    return -EINVAL;
    }

    + if (attr->sample_type & PERF_SAMPLE_STACK) {
    + /* Mode must be specified. */
    + if (attr->sample_stack & ~(PERF_SAMPLE_STACK_MAX-1))
    + return -EINVAL;
    +
    + /* Validate registers mask for user mode. */
    + if ((attr->sample_stack & PERF_SAMPLE_STACK_USER) &&
    + (!attr->sample_stack_user))
    + return -EINVAL;
    + } else {
    + /*
    + * Stack dump not required in sample, all stack
    + * settings should be zero.
    + */
    + if (attr->sample_stack)
    + return -EINVAL;
    + if (attr->sample_stack_user)
    + return -EINVAL;
    + }
    +
    out:
    return ret;

    --
    1.7.7.6


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