2021-06-27 13:18:09 +00:00
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perf-dlfilter(1)
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================
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NAME
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----
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perf-dlfilter - Filter sample events using a dynamically loaded shared
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object file
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SYNOPSIS
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--------
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[verse]
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2021-06-27 13:18:12 +00:00
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'perf script' [--dlfilter file.so ] [ --dlarg arg ]...
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2021-06-27 13:18:09 +00:00
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DESCRIPTION
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-----------
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This option is used to process data through a custom filter provided by a
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2021-06-27 13:18:12 +00:00
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dynamically loaded shared object file. Arguments can be passed using --dlarg
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and retrieved using perf_dlfilter_fns.args().
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2021-06-27 13:18:09 +00:00
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If 'file.so' does not contain "/", then it will be found either in the current
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directory, or perf tools exec path which is ~/libexec/perf-core/dlfilters for
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a local build and install (refer perf --exec-path), or the dynamic linker
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paths.
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API
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---
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The API for filtering consists of the following:
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[source,c]
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----
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#include <perf/perf_dlfilter.h>
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const struct perf_dlfilter_fns perf_dlfilter_fns;
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int start(void **data, void *ctx);
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int stop(void *data, void *ctx);
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int filter_event(void *data, const struct perf_dlfilter_sample *sample, void *ctx);
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int filter_event_early(void *data, const struct perf_dlfilter_sample *sample, void *ctx);
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const char *filter_description(const char **long_description);
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----
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If implemented, 'start' will be called at the beginning, before any
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calls to 'filter_event' or 'filter_event_early'. Return 0 to indicate success,
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or return a negative error code. '*data' can be assigned for use by other
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functions. 'ctx' is needed for calls to perf_dlfilter_fns, but most
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perf_dlfilter_fns are not valid when called from 'start'.
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If implemented, 'stop' will be called at the end, after any calls to
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'filter_event' or 'filter_event_early'. Return 0 to indicate success, or
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return a negative error code. 'data' is set by 'start'. 'ctx' is needed
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for calls to perf_dlfilter_fns, but most perf_dlfilter_fns are not valid
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when called from 'stop'.
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If implemented, 'filter_event' will be called for each sample event.
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Return 0 to keep the sample event, 1 to filter it out, or return a negative
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error code. 'data' is set by 'start'. 'ctx' is needed for calls to
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'perf_dlfilter_fns'.
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'filter_event_early' is the same as 'filter_event' except it is called before
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internal filtering.
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2021-06-27 13:18:11 +00:00
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If implemented, 'filter_description' should return a one-line description
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of the filter, and optionally a longer description.
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2021-06-27 13:18:09 +00:00
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The perf_dlfilter_sample structure
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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'filter_event' and 'filter_event_early' are passed a perf_dlfilter_sample
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structure, which contains the following fields:
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[source,c]
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----
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/*
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* perf sample event information (as per perf script and <linux/perf_event.h>)
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*/
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struct perf_dlfilter_sample {
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__u32 size; /* Size of this structure (for compatibility checking) */
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__u16 ins_lat; /* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
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__u16 p_stage_cyc; /* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
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__u64 ip;
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__s32 pid;
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__s32 tid;
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__u64 time;
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__u64 addr;
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__u64 id;
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__u64 stream_id;
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__u64 period;
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__u64 weight; /* Refer PERF_SAMPLE_WEIGHT_TYPE in <linux/perf_event.h> */
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__u64 transaction; /* Refer PERF_SAMPLE_TRANSACTION in <linux/perf_event.h> */
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__u64 insn_cnt; /* For instructions-per-cycle (IPC) */
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__u64 cyc_cnt; /* For instructions-per-cycle (IPC) */
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__s32 cpu;
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__u32 flags; /* Refer PERF_DLFILTER_FLAG_* above */
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__u64 data_src; /* Refer PERF_SAMPLE_DATA_SRC in <linux/perf_event.h> */
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__u64 phys_addr; /* Refer PERF_SAMPLE_PHYS_ADDR in <linux/perf_event.h> */
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__u64 data_page_size; /* Refer PERF_SAMPLE_DATA_PAGE_SIZE in <linux/perf_event.h> */
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__u64 code_page_size; /* Refer PERF_SAMPLE_CODE_PAGE_SIZE in <linux/perf_event.h> */
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__u64 cgroup; /* Refer PERF_SAMPLE_CGROUP in <linux/perf_event.h> */
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__u8 cpumode; /* Refer CPUMODE_MASK etc in <linux/perf_event.h> */
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__u8 addr_correlates_sym; /* True => resolve_addr() can be called */
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__u16 misc; /* Refer perf_event_header in <linux/perf_event.h> */
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__u32 raw_size; /* Refer PERF_SAMPLE_RAW in <linux/perf_event.h> */
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const void *raw_data; /* Refer PERF_SAMPLE_RAW in <linux/perf_event.h> */
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__u64 brstack_nr; /* Number of brstack entries */
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const struct perf_branch_entry *brstack; /* Refer <linux/perf_event.h> */
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__u64 raw_callchain_nr; /* Number of raw_callchain entries */
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const __u64 *raw_callchain; /* Refer <linux/perf_event.h> */
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const char *event;
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};
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----
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The perf_dlfilter_fns structure
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'perf_dlfilter_fns' structure is populated with function pointers when the
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file is loaded. The functions can be called by 'filter_event' or
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'filter_event_early'.
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[source,c]
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----
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struct perf_dlfilter_fns {
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const struct perf_dlfilter_al *(*resolve_ip)(void *ctx);
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const struct perf_dlfilter_al *(*resolve_addr)(void *ctx);
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char **(*args)(void *ctx, int *dlargc);
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__s32 (*resolve_address)(void *ctx, __u64 address, struct perf_dlfilter_al *al);
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const __u8 *(*insn)(void *ctx, __u32 *length);
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const char *(*srcline)(void *ctx, __u32 *line_number);
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void *(*reserved[122])(void *);
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};
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----
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'resolve_ip' returns information about ip.
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'resolve_addr' returns information about addr (if addr_correlates_sym).
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'args' returns arguments from --dlarg options.
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'resolve_address' provides information about 'address'. al->size must be set
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before calling. Returns 0 on success, -1 otherwise.
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'insn' returns instruction bytes and length.
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'srcline' return source file name and line number.
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The perf_dlfilter_al structure
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'perf_dlfilter_al' structure contains information about an address.
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[source,c]
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----
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/*
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* Address location (as per perf script)
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*/
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struct perf_dlfilter_al {
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__u32 size; /* Size of this structure (for compatibility checking) */
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__u32 symoff;
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const char *sym;
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__u64 addr; /* Mapped address (from dso) */
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__u64 sym_start;
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__u64 sym_end;
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const char *dso;
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__u8 sym_binding; /* STB_LOCAL, STB_GLOBAL or STB_WEAK, refer <elf.h> */
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__u8 is_64_bit; /* Only valid if dso is not NULL */
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__u8 is_kernel_ip; /* True if in kernel space */
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__u32 buildid_size;
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__u8 *buildid;
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/* Below members are only populated by resolve_ip() */
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__u8 filtered; /* true if this sample event will be filtered out */
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const char *comm;
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};
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----
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perf_dlfilter_sample flags
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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The 'flags' member of 'perf_dlfilter_sample' corresponds with the flags field
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of perf script. The bits of the flags are as follows:
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[source,c]
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----
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/* Definitions for perf_dlfilter_sample flags */
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enum {
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PERF_DLFILTER_FLAG_BRANCH = 1ULL << 0,
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PERF_DLFILTER_FLAG_CALL = 1ULL << 1,
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PERF_DLFILTER_FLAG_RETURN = 1ULL << 2,
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PERF_DLFILTER_FLAG_CONDITIONAL = 1ULL << 3,
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PERF_DLFILTER_FLAG_SYSCALLRET = 1ULL << 4,
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PERF_DLFILTER_FLAG_ASYNC = 1ULL << 5,
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PERF_DLFILTER_FLAG_INTERRUPT = 1ULL << 6,
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PERF_DLFILTER_FLAG_TX_ABORT = 1ULL << 7,
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PERF_DLFILTER_FLAG_TRACE_BEGIN = 1ULL << 8,
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PERF_DLFILTER_FLAG_TRACE_END = 1ULL << 9,
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PERF_DLFILTER_FLAG_IN_TX = 1ULL << 10,
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PERF_DLFILTER_FLAG_VMENTRY = 1ULL << 11,
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PERF_DLFILTER_FLAG_VMEXIT = 1ULL << 12,
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};
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----
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EXAMPLE
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-------
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Filter out everything except branches from "foo" to "bar":
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[source,c]
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----
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#include <perf/perf_dlfilter.h>
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#include <string.h>
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const struct perf_dlfilter_fns perf_dlfilter_fns;
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int filter_event(void *data, const struct perf_dlfilter_sample *sample, void *ctx)
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{
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const struct perf_dlfilter_al *al;
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const struct perf_dlfilter_al *addr_al;
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if (!sample->ip || !sample->addr_correlates_sym)
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return 1;
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al = perf_dlfilter_fns.resolve_ip(ctx);
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if (!al || !al->sym || strcmp(al->sym, "foo"))
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return 1;
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addr_al = perf_dlfilter_fns.resolve_addr(ctx);
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if (!addr_al || !addr_al->sym || strcmp(addr_al->sym, "bar"))
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return 1;
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return 0;
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}
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----
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To build the shared object, assuming perf has been installed for the local user
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i.e. perf_dlfilter.h is in ~/include/perf :
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gcc -c -I ~/include -fpic dlfilter-example.c
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gcc -shared -o dlfilter-example.so dlfilter-example.o
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To use the filter with perf script:
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perf script --dlfilter dlfilter-example.so
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SEE ALSO
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--------
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linkperf:perf-script[1]
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