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>

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.

Do not assume the 'sample' argument is valid (dereferenceable)
after 'filter_event' and 'filter_event_early' return.

Do not assume data referenced by pointers in struct perf_dlfilter_sample
is valid (dereferenceable) after 'filter_event' and 'filter_event_early' return.

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;
	__s32 machine_pid;
	__s32 vcpu;
};
----

Note: 'machine_pid' and 'vcpu' are not original members, but were added together later.
'size' can be used to determine their presence at run time.
PERF_DLFILTER_HAS_MACHINE_PID will be defined if they are present at compile time.
For example:
[source,c]
----
#include <perf/perf_dlfilter.h>
#include <stddef.h>
#include <stdbool.h>

static inline bool have_machine_pid(const struct perf_dlfilter_sample *sample)
{
#ifdef PERF_DLFILTER_HAS_MACHINE_PID
	return sample->size >= offsetof(struct perf_dlfilter_sample, vcpu) + sizeof(sample->vcpu);
#else
	return false;
#endif
}
----

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 (*al_cleanup)(void *ctx, struct perf_dlfilter_al *al);
	void *(*reserved[119])(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. Call al_cleanup() (if present,
see below) when 'al' data is no longer needed.

'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.

'al_cleanup' must be called (if present, so check perf_dlfilter_fns.al_cleanup != NULL)
after resolve_address() to free any associated resources.

Do not assume pointers obtained via perf_dlfilter_fns are valid (dereferenceable)
after 'filter_event' and 'filter_event_early' return.

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;
	void *priv; /* Private data. Do not change */
};
----

Do not assume data referenced by pointers in struct perf_dlfilter_al
is valid (dereferenceable) after 'filter_event' and 'filter_event_early' return.

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>

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

NOTES
-----

The dlfilter .so file will be dependent on shared libraries. If those change,
it may be necessary to rebuild the .so. Also there may be unexpected results
if the .so uses different versions of the shared libraries that perf uses.
Versions can be checked using the ldd command.

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