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    Subject[PATCH 17/22] perf tools: Generate prologue for BPF programs
    Date
    This patch generates prologue for each 'struct probe_trace_event' for
    fetching arguments for BPF programs.

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

    Signed-off-by: Wang Nan <wangnan0@huawei.com>
    Cc: Alexei Starovoitov <ast@plumgrid.com>
    Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
    Cc: Daniel Borkmann <daniel@iogearbox.net>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: He Kuang <hekuang@huawei.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Kaixu Xia <xiakaixu@huawei.com>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Zefan Li <lizefan@huawei.com>
    Cc: pi3orama@163.com
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Link: http://lkml.kernel.org/n/ebpf-6yw9eg0ej3l4jnqhinngkw86@git.kernel.org
    ---
    tools/perf/util/bpf-loader.c | 120 ++++++++++++++++++++++++++++++++++++++++++-
    1 file changed, 119 insertions(+), 1 deletion(-)

    diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
    index f4c690f..c363907 100644
    --- a/tools/perf/util/bpf-loader.c
    +++ b/tools/perf/util/bpf-loader.c
    @@ -5,11 +5,14 @@
    * Copyright (C) 2015 Huawei Inc.
    */

    +#include <linux/bpf.h>
    #include <bpf/libbpf.h>
    #include <linux/err.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"
    @@ -32,6 +35,8 @@ DEFINE_PRINT_FN(debug, 1)

    struct bpf_prog_priv {
    struct perf_probe_event pev;
    + bool need_prologue;
    + struct bpf_insn *insns_buf;
    };

    struct bpf_object *
    @@ -98,6 +103,7 @@ 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);
    }

    @@ -189,6 +195,102 @@ 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 -EINVAL;
    +}
    +
    +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 -EINVAL;
    + }
    +
    + 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 tev doesn'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;
    @@ -223,6 +325,18 @@ 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;
    @@ -306,7 +420,11 @@ int bpf__foreach_tev(struct bpf_object *obj,
    for (i = 0; i < pev->ntevs; i++) {
    tev = &pev->tevs[i];

    - fd = bpf_program__fd(prog);
    + 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;
    --
    1.8.3.4


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