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: Wang 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: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 119 insertions, 1 deletions

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index bd14be438cda..190a1c7f0649 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -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];
 
-                        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;