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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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