tools/perf/Documentation/perf-dlfilter.txt

perf-dlfilter(1)
================

NAME
----
perf-dlfilter - Filter sample events using a dynamically loaded shared
object file

SYNOPSIS
--------
[verse]
'perf script' [--dlfilter file.so ] [ --dlarg arg ]...

DESCRIPTION
-----------

This option is used to process data through a custom filter provided by a
dynamically loaded shared object file. Arguments can be passed using --dlarg
and retrieved using perf_dlfilter_fns.args().

If 'file.so' does not contain "/", then it will be found either in the current
directory, or perf tools exec path which is ~/libexec/perf-core/dlfilters for
a local build and install (refer perf --exec-path), or the dynamic linker
paths.

API
---

The API for filtering consists of the following:

[source,c]
----
#include <perf/perf_dlfilter.h>

const struct perf_dlfilter_fns perf_dlfilter_fns;

int start(void **data, void *ctx);
int stop(void *data, void *ctx);
int filter_event(void *data, const struct perf_dlfilter_sample *sample, void *ctx);
int filter_event_early(void *data, const struct perf_dlfilter_sample *sample, void *ctx);
const char *filter_description(const char **long_description);
----

If implemented, 'start' will be called at the beginning, before any
calls to 'filter_event' or 'filter_event_early'. Return 0 to indicate success,
or return a negative error code. '*data' can be assigned for use by other
functions. 'ctx' is needed for calls to perf_dlfilter_fns, but most
perf_dlfilter_fns are not valid when called from 'start'.

If implemented, 'stop' will be called at the end, after any calls to
'filter_event' or 'filter_event_early'. Return 0 to indicate success, or
return a negative error code. 'data' is set by 'start'. 'ctx' is needed
for calls to perf_dlfilter_fns, but most perf_dlfilter_fns are not valid
when called from 'stop'.

If implemented, 'filter_event' will be called for each sample event.
Return 0 to keep the sample event, 1 to filter it out, or return a negative
error code. 'data' is set by 'start'. 'ctx' is needed for calls to
'perf_dlfilter_fns'.

'filter_event_early' is the same as 'filter_event' except it is called before
internal filtering.

If implemented, 'filter_description' should return a one-line description
of the filter, and optionally a longer description.

The perf_dlfilter_sample structure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

'filter_event' and 'filter_event_early' are passed a perf_dlfilter_sample
structure, which contains the following fields:
[source,c]
----
/*
 * perf sample event information (as per perf script and <linux/perf_event.h>)
 */
struct perf_dlfilter_sample {
	__u32 size; /* Size of this structure (for compatibility checking) */
	__u16 ins_lat;		/* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
	__u16 p_stage_cyc;	/* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
	__u64 ip;
	__s32 pid;
	__s32 tid;
	__u64 time;
	__u64 addr;
	__u64 id;
	__u64 stream_id;
	__u64 period;
	__u64 weight;		/* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
	__u64 transaction;	/* Refer PERF_SAMPLE_TRANSACTION in <linux/perf_event.h> */
	__u64 insn_cnt;	/* For instructions-per-cycle (IPC) */
	__u64 cyc_cnt;		/* For instructions-per-cycle (IPC) */
	__s32 cpu;
	__u32 flags;		/* Refer PERF_DLFILTER_FLAG_* above */
	__u64 data_src;		/* Refer PERF_SAMPLE_DATA_SRC in <linux/perf_event.h> */
	__u64 phys_addr;	/* Refer PERF_SAMPLE_PHYS_ADDR in <linux/perf_event.h> */
	__u64 data_page_size;	/* Refer PERF_SAMPLE_DATA_PAGE_SIZE in <linux/perf_event.h> */
	__u64 code_page_size;	/* Refer PERF_SAMPLE_CODE_PAGE_SIZE in <linux/perf_event.h> */
	__u64 cgroup;		/* Refer PERF_SAMPLE_CGROUP in <linux/perf_event.h> */
	__u8  cpumode;		/* Refer CPUMODE_MASK etc in <linux/perf_event.h> */
	__u8  addr_correlates_sym; /* True => resolve_addr() can be called */
	__u16 misc;		/* Refer perf_event_header in <linux/perf_event.h> */
	__u32 raw_size;		/* Refer PERF_SAMPLE_RAW in <linux/perf_event.h> */
	const void *raw_data;	/* Refer PERF_SAMPLE_RAW in <linux/perf_event.h> */
	__u64 brstack_nr;	/* Number of brstack entries */
	const struct perf_branch_entry *brstack; /* Refer <linux/perf_event.h> */
	__u64 raw_callchain_nr;	/* Number of raw_callchain entries */
	const __u64 *raw_callchain; /* Refer <linux/perf_event.h> */
	const char *event;
};
----

The perf_dlfilter_fns structure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The 'perf_dlfilter_fns' structure is populated with function pointers when the
file is loaded. The functions can be called by 'filter_event' or
'filter_event_early'.

[source,c]
----
struct perf_dlfilter_fns {
	const struct perf_dlfilter_al *(*resolve_ip)(void *ctx);
	const struct perf_dlfilter_al *(*resolve_addr)(void *ctx);
	char **(*args)(void *ctx, int *dlargc);
	__s32 (*resolve_address)(void *ctx, __u64 address, struct perf_dlfilter_al *al);
	const __u8 *(*insn)(void *ctx, __u32 *length);
	const char *(*srcline)(void *ctx, __u32 *line_number);
	struct perf_event_attr *(*attr)(void *ctx);
	__s32 (*object_code)(void *ctx, __u64 ip, void *buf, __u32 len);
	void *(*reserved[120])(void *);
};
----

'resolve_ip' returns information about ip.

'resolve_addr' returns information about addr (if addr_correlates_sym).

'args' returns arguments from --dlarg options.

'resolve_address' provides information about 'address'. al->size must be set
before calling. Returns 0 on success, -1 otherwise.

'insn' returns instruction bytes and length.

'srcline' return source file name and line number.

'attr' returns perf_event_attr, refer <linux/perf_event.h>.

'object_code' reads object code and returns the number of bytes read.

The perf_dlfilter_al structure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The 'perf_dlfilter_al' structure contains information about an address.

[source,c]
----
/*
 * Address location (as per perf script)
 */
struct perf_dlfilter_al {
	__u32 size; /* Size of this structure (for compatibility checking) */
	__u32 symoff;
	const char *sym;
	__u64 addr; /* Mapped address (from dso) */
	__u64 sym_start;
	__u64 sym_end;
	const char *dso;
	__u8  sym_binding; /* STB_LOCAL, STB_GLOBAL or STB_WEAK, refer <elf.h> */
	__u8  is_64_bit; /* Only valid if dso is not NULL */
	__u8  is_kernel_ip; /* True if in kernel space */
	__u32 buildid_size;
	__u8 *buildid;
	/* Below members are only populated by resolve_ip() */
	__u8 filtered; /* true if this sample event will be filtered out */
	const char *comm;
};
----

perf_dlfilter_sample flags
~~~~~~~~~~~~~~~~~~~~~~~~~~

The 'flags' member of 'perf_dlfilter_sample' corresponds with the flags field
of perf script. The bits of the flags are as follows:

[source,c]
----
/* Definitions for perf_dlfilter_sample flags */
enum {
	PERF_DLFILTER_FLAG_BRANCH	= 1ULL << 0,
	PERF_DLFILTER_FLAG_CALL		= 1ULL << 1,
	PERF_DLFILTER_FLAG_RETURN	= 1ULL << 2,
	PERF_DLFILTER_FLAG_CONDITIONAL	= 1ULL << 3,
	PERF_DLFILTER_FLAG_SYSCALLRET	= 1ULL << 4,
	PERF_DLFILTER_FLAG_ASYNC	= 1ULL << 5,
	PERF_DLFILTER_FLAG_INTERRUPT	= 1ULL << 6,
	PERF_DLFILTER_FLAG_TX_ABORT	= 1ULL << 7,
	PERF_DLFILTER_FLAG_TRACE_BEGIN	= 1ULL << 8,
	PERF_DLFILTER_FLAG_TRACE_END	= 1ULL << 9,
	PERF_DLFILTER_FLAG_IN_TX	= 1ULL << 10,
	PERF_DLFILTER_FLAG_VMENTRY	= 1ULL << 11,
	PERF_DLFILTER_FLAG_VMEXIT	= 1ULL << 12,
};
----

EXAMPLE
-------

Filter out everything except branches from "foo" to "bar":

[source,c]
----
#include <perf/perf_dlfilter.h>
#include <string.h>

const struct perf_dlfilter_fns perf_dlfilter_fns;

int filter_event(void *data, const struct perf_dlfilter_sample *sample, void *ctx)
{
	const struct perf_dlfilter_al *al;
	const struct perf_dlfilter_al *addr_al;

	if (!sample->ip || !sample->addr_correlates_sym)
		return 1;

	al = perf_dlfilter_fns.resolve_ip(ctx);
	if (!al || !al->sym || strcmp(al->sym, "foo"))
		return 1;

	addr_al = perf_dlfilter_fns.resolve_addr(ctx);
	if (!addr_al || !addr_al->sym || strcmp(addr_al->sym, "bar"))
		return 1;

	return 0;
}
----

To build the shared object, assuming perf has been installed for the local user
i.e. perf_dlfilter.h is in ~/include/perf :

	gcc -c -I ~/include -fpic dlfilter-example.c
	gcc -shared -o dlfilter-example.so dlfilter-example.o

To use the filter with perf script:

	perf script --dlfilter dlfilter-example.so

SEE ALSO
--------
linkperf:perf-script[1]