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Commit a08357d8 authored by Wang Nan's avatar Wang Nan Committed by Arnaldo Carvalho de Melo
Browse files

perf bpf: Generate prologue for BPF programs 



This patch generates a prologue for each 'struct probe_trace_event' for
fetching arguments for BPF programs.

After bpf__probe(), iterate over each program to check whether prologues are
required. If none of the 'struct perf_probe_event' programs will attach to have
at least one argument, simply skip preprocessor hooking. For those who a
prologue is required, call bpf__gen_prologue() and paste the original
instruction after the prologue.

Signed-off-by: default avatarWang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1447675815-166222-12-git-send-email-wangnan0@huawei.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent bfc077b4

tools/perf/util/bpf-loader.c

+119 −1
Original line number Diff line number Diff line
@@ -5,12 +5,15 @@ 
 * Copyright (C) 2015 Huawei Inc.

 */



#include <linux/bpf.h>

#include <bpf/libbpf.h>

#include <linux/err.h>

#include <linux/string.h>

#include "perf.h"

#include "debug.h"

#include "bpf-loader.h"

#include "bpf-prologue.h"

#include "llvm-utils.h"

#include "probe-event.h"

#include "probe-finder.h" // for MAX_PROBES

#include "llvm-utils.h"
@@ -33,6 +36,8 @@ DEFINE_PRINT_FN(debug, 1) 


struct bpf_prog_priv {

	struct perf_probe_event pev;

	bool need_prologue;

	struct bpf_insn *insns_buf;

};



static bool libbpf_initialized;
@@ -107,6 +112,7 @@ bpf_prog_priv__clear(struct bpf_program *prog __maybe_unused, 
	struct bpf_prog_priv *priv = _priv;



	cleanup_perf_probe_events(&priv->pev, 1);

	zfree(&priv->insns_buf);

	free(priv);

}
@@ -365,6 +371,102 @@ static int bpf__prepare_probe(void) 
	return err;

}



static int

preproc_gen_prologue(struct bpf_program *prog, int n,

		     struct bpf_insn *orig_insns, int orig_insns_cnt,

		     struct bpf_prog_prep_result *res)

{

	struct probe_trace_event *tev;

	struct perf_probe_event *pev;

	struct bpf_prog_priv *priv;

	struct bpf_insn *buf;

	size_t prologue_cnt = 0;

	int err;



	err = bpf_program__get_private(prog, (void **)&priv);

	if (err || !priv)

		goto errout;



	pev = &priv->pev;



	if (n < 0 || n >= pev->ntevs)

		goto errout;



	tev = &pev->tevs[n];



	buf = priv->insns_buf;

	err = bpf__gen_prologue(tev->args, tev->nargs,

				buf, &prologue_cnt,

				BPF_MAXINSNS - orig_insns_cnt);

	if (err) {

		const char *title;



		title = bpf_program__title(prog, false);

		if (!title)

			title = "[unknown]";



		pr_debug("Failed to generate prologue for program %s\n",

			 title);

		return err;

	}



	memcpy(&buf[prologue_cnt], orig_insns,

	       sizeof(struct bpf_insn) * orig_insns_cnt);



	res->new_insn_ptr = buf;

	res->new_insn_cnt = prologue_cnt + orig_insns_cnt;

	res->pfd = NULL;

	return 0;



errout:

	pr_debug("Internal error in preproc_gen_prologue\n");

	return -BPF_LOADER_ERRNO__PROLOGUE;

}



static int hook_load_preprocessor(struct bpf_program *prog)

{

	struct perf_probe_event *pev;

	struct bpf_prog_priv *priv;

	bool need_prologue = false;

	int err, i;



	err = bpf_program__get_private(prog, (void **)&priv);

	if (err || !priv) {

		pr_debug("Internal error when hook preprocessor\n");

		return -BPF_LOADER_ERRNO__INTERNAL;

	}



	pev = &priv->pev;

	for (i = 0; i < pev->ntevs; i++) {

		struct probe_trace_event *tev = &pev->tevs[i];



		if (tev->nargs > 0) {

			need_prologue = true;

			break;

		}

	}



	/*

	 * Since all tevs don't have argument, we don't need generate

	 * prologue.

	 */

	if (!need_prologue) {

		priv->need_prologue = false;

		return 0;

	}



	priv->need_prologue = true;

	priv->insns_buf = malloc(sizeof(struct bpf_insn) * BPF_MAXINSNS);

	if (!priv->insns_buf) {

		pr_debug("No enough memory: alloc insns_buf failed\n");

		return -ENOMEM;

	}



	err = bpf_program__set_prep(prog, pev->ntevs,

				    preproc_gen_prologue);

	return err;

}



int bpf__probe(struct bpf_object *obj)

{

	int err = 0;
@@ -399,6 +501,18 @@ int bpf__probe(struct bpf_object *obj) 
			pr_debug("bpf_probe: failed to apply perf probe events");

			goto out;

		}



		/*

		 * After probing, let's consider prologue, which

		 * adds program fetcher to BPF programs.

		 *

		 * hook_load_preprocessorr() hooks pre-processor

		 * to bpf_program, let it generate prologue

		 * dynamically during loading.

		 */

		err = hook_load_preprocessor(prog);

		if (err)

			goto out;

	}

out:

	return err < 0 ? err : 0;
@@ -482,7 +596,11 @@ int bpf__foreach_tev(struct bpf_object *obj, 
		for (i = 0; i < pev->ntevs; i++) {

			tev = &pev->tevs[i];



			if (priv->need_prologue)

				fd = bpf_program__nth_fd(prog, i);

			else

				fd = bpf_program__fd(prog);



			if (fd < 0) {

				pr_debug("bpf: failed to get file descriptor\n");

				return fd;