From 5f4e821c6c90dd6d471981735cec456f669f0e59 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Thu, 16 Jun 2022 22:22:14 +0200 Subject: [PATCH] perf tools: Rework prologue generation code Some functions we use for bpf prologue generation are going to be deprecated. This change reworks current code not to use them. We need to replace following functions/struct: bpf_program__set_prep bpf_program__nth_fd struct bpf_prog_prep_result Currently we use bpf_program__set_prep to hook perf callback before program is loaded and provide new instructions with the prologue. We replace this function/ality by taking instructions for specific program, attaching prologue to them and load such new ebpf programs with prologue using separate bpf_prog_load calls (outside libbpf load machinery). Before we can take and use program instructions, we need libbpf to actually load it. This way we get the final shape of its instructions with all relocations and verifier adjustments). There's one glitch though.. perf kprobe program already assumes generated prologue code with proper values in argument registers, so loading such program directly will fail in the verifier. That's where the fallback pre-load handler fits in and prepends the initialization code to the program. Once such program is loaded we take its instructions, cut off the initialization code and prepend the prologue. I know.. sorry ;-) To have access to the program when loading this patch adds support to register 'fallback' section handler to take care of perf kprobe programs. The fallback means that it handles any section definition besides the ones that libbpf handles. The handler serves two purposes: - allows perf programs to have special arguments in section name - allows perf to use pre-load callback where we can attach init code (zeroing all argument registers) to each perf program Suggested-by: Andrii Nakryiko Signed-off-by: Jiri Olsa Tested-by: Arnaldo Carvalho de Melo Acked-by: Arnaldo Carvalho de Melo Cc: Alexander Shishkin Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: Ian Rogers Cc: Ingo Molnar Cc: John Fastabend Cc: Martin KaFai Lau Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Song Liu Cc: Yonghong Song Cc: bpf@vger.kernel.org Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/20220616202214.70359-2-jolsa@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/bpf-loader.c | 204 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 175 insertions(+), 29 deletions(-) diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c index cdd6463..d2c9b09 100644 --- a/tools/perf/util/bpf-loader.c +++ b/tools/perf/util/bpf-loader.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -49,6 +50,7 @@ struct bpf_prog_priv { struct bpf_insn *insns_buf; int nr_types; int *type_mapping; + int *prologue_fds; }; struct bpf_perf_object { @@ -56,6 +58,11 @@ struct bpf_perf_object { struct bpf_object *obj; }; +struct bpf_preproc_result { + struct bpf_insn *new_insn_ptr; + int new_insn_cnt; +}; + static LIST_HEAD(bpf_objects_list); static struct hashmap *bpf_program_hash; static struct hashmap *bpf_map_hash; @@ -82,6 +89,7 @@ bpf_perf_object__next(struct bpf_perf_object *prev) (perf_obj) = (tmp), (tmp) = bpf_perf_object__next(tmp)) static bool libbpf_initialized; +static int libbpf_sec_handler; static int bpf_perf_object__add(struct bpf_object *obj) { @@ -95,12 +103,76 @@ static int bpf_perf_object__add(struct bpf_object *obj) return perf_obj ? 0 : -ENOMEM; } +static void *program_priv(const struct bpf_program *prog) +{ + void *priv; + + if (IS_ERR_OR_NULL(bpf_program_hash)) + return NULL; + if (!hashmap__find(bpf_program_hash, prog, &priv)) + return NULL; + return priv; +} + +static struct bpf_insn prologue_init_insn[] = { + BPF_MOV64_IMM(BPF_REG_2, 0), + BPF_MOV64_IMM(BPF_REG_3, 0), + BPF_MOV64_IMM(BPF_REG_4, 0), + BPF_MOV64_IMM(BPF_REG_5, 0), +}; + +static int libbpf_prog_prepare_load_fn(struct bpf_program *prog, + struct bpf_prog_load_opts *opts __maybe_unused, + long cookie __maybe_unused) +{ + size_t init_size_cnt = ARRAY_SIZE(prologue_init_insn); + size_t orig_insn_cnt, insn_cnt, init_size, orig_size; + struct bpf_prog_priv *priv = program_priv(prog); + const struct bpf_insn *orig_insn; + struct bpf_insn *insn; + + if (IS_ERR_OR_NULL(priv)) { + pr_debug("bpf: failed to get private field\n"); + return -BPF_LOADER_ERRNO__INTERNAL; + } + + if (!priv->need_prologue) + return 0; + + /* prepend initialization code to program instructions */ + orig_insn = bpf_program__insns(prog); + orig_insn_cnt = bpf_program__insn_cnt(prog); + init_size = init_size_cnt * sizeof(*insn); + orig_size = orig_insn_cnt * sizeof(*insn); + + insn_cnt = orig_insn_cnt + init_size_cnt; + insn = malloc(insn_cnt * sizeof(*insn)); + if (!insn) + return -ENOMEM; + + memcpy(insn, prologue_init_insn, init_size); + memcpy((char *) insn + init_size, orig_insn, orig_size); + bpf_program__set_insns(prog, insn, insn_cnt); + return 0; +} + static int libbpf_init(void) { + LIBBPF_OPTS(libbpf_prog_handler_opts, handler_opts, + .prog_prepare_load_fn = libbpf_prog_prepare_load_fn, + ); + if (libbpf_initialized) return 0; libbpf_set_print(libbpf_perf_print); + libbpf_sec_handler = libbpf_register_prog_handler(NULL, BPF_PROG_TYPE_KPROBE, + 0, &handler_opts); + if (libbpf_sec_handler < 0) { + pr_debug("bpf: failed to register libbpf section handler: %d\n", + libbpf_sec_handler); + return -BPF_LOADER_ERRNO__INTERNAL; + } libbpf_initialized = true; return 0; } @@ -184,14 +256,31 @@ struct bpf_object *bpf__prepare_load(const char *filename, bool source) return obj; } +static void close_prologue_programs(struct bpf_prog_priv *priv) +{ + struct perf_probe_event *pev; + int i, fd; + + if (!priv->need_prologue) + return; + pev = &priv->pev; + for (i = 0; i < pev->ntevs; i++) { + fd = priv->prologue_fds[i]; + if (fd != -1) + close(fd); + } +} + static void clear_prog_priv(const struct bpf_program *prog __maybe_unused, void *_priv) { struct bpf_prog_priv *priv = _priv; + close_prologue_programs(priv); cleanup_perf_probe_events(&priv->pev, 1); zfree(&priv->insns_buf); + zfree(&priv->prologue_fds); zfree(&priv->type_mapping); zfree(&priv->sys_name); zfree(&priv->evt_name); @@ -239,17 +328,6 @@ static bool ptr_equal(const void *key1, const void *key2, return key1 == key2; } -static void *program_priv(const struct bpf_program *prog) -{ - void *priv; - - if (IS_ERR_OR_NULL(bpf_program_hash)) - return NULL; - if (!hashmap__find(bpf_program_hash, prog, &priv)) - return NULL; - return priv; -} - static int program_set_priv(struct bpf_program *prog, void *priv) { void *old_priv; @@ -554,8 +632,8 @@ static int bpf__prepare_probe(void) 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) + const struct bpf_insn *orig_insns, int orig_insns_cnt, + struct bpf_preproc_result *res) { struct bpf_prog_priv *priv = program_priv(prog); struct probe_trace_event *tev; @@ -603,7 +681,6 @@ preproc_gen_prologue(struct bpf_program *prog, int n, res->new_insn_ptr = buf; res->new_insn_cnt = prologue_cnt + orig_insns_cnt; - res->pfd = NULL; return 0; errout: @@ -711,7 +788,7 @@ static int hook_load_preprocessor(struct bpf_program *prog) struct bpf_prog_priv *priv = program_priv(prog); struct perf_probe_event *pev; bool need_prologue = false; - int err, i; + int i; if (IS_ERR_OR_NULL(priv)) { pr_debug("Internal error when hook preprocessor\n"); @@ -749,6 +826,13 @@ static int hook_load_preprocessor(struct bpf_program *prog) return -ENOMEM; } + priv->prologue_fds = malloc(sizeof(int) * pev->ntevs); + if (!priv->prologue_fds) { + pr_debug("Not enough memory: alloc prologue fds failed\n"); + return -ENOMEM; + } + memset(priv->prologue_fds, -1, sizeof(int) * pev->ntevs); + priv->type_mapping = malloc(sizeof(int) * pev->ntevs); if (!priv->type_mapping) { pr_debug("Not enough memory: alloc type_mapping failed\n"); @@ -757,13 +841,7 @@ static int hook_load_preprocessor(struct bpf_program *prog) memset(priv->type_mapping, -1, sizeof(int) * pev->ntevs); - err = map_prologue(pev, priv->type_mapping, &priv->nr_types); - if (err) - return err; - - err = bpf_program__set_prep(prog, priv->nr_types, - preproc_gen_prologue); - return err; + return map_prologue(pev, priv->type_mapping, &priv->nr_types); } int bpf__probe(struct bpf_object *obj) @@ -870,6 +948,77 @@ int bpf__unprobe(struct bpf_object *obj) return ret; } +static int bpf_object__load_prologue(struct bpf_object *obj) +{ + int init_cnt = ARRAY_SIZE(prologue_init_insn); + const struct bpf_insn *orig_insns; + struct bpf_preproc_result res; + struct perf_probe_event *pev; + struct bpf_program *prog; + int orig_insns_cnt; + + bpf_object__for_each_program(prog, obj) { + struct bpf_prog_priv *priv = program_priv(prog); + int err, i, fd; + + if (IS_ERR_OR_NULL(priv)) { + pr_debug("bpf: failed to get private field\n"); + return -BPF_LOADER_ERRNO__INTERNAL; + } + + if (!priv->need_prologue) + continue; + + /* + * For each program that needs prologue we do following: + * + * - take its current instructions and use them + * to generate the new code with prologue + * - load new instructions with bpf_prog_load + * and keep the fd in prologue_fds + * - new fd will be used in bpf__foreach_event + * to connect this program with perf evsel + */ + orig_insns = bpf_program__insns(prog); + orig_insns_cnt = bpf_program__insn_cnt(prog); + + pev = &priv->pev; + for (i = 0; i < pev->ntevs; i++) { + /* + * Skipping artificall prologue_init_insn instructions + * (init_cnt), so the prologue can be generated instead + * of them. + */ + err = preproc_gen_prologue(prog, i, + orig_insns + init_cnt, + orig_insns_cnt - init_cnt, + &res); + if (err) + return err; + + fd = bpf_prog_load(bpf_program__get_type(prog), + bpf_program__name(prog), "GPL", + res.new_insn_ptr, + res.new_insn_cnt, NULL); + if (fd < 0) { + char bf[128]; + + libbpf_strerror(-errno, bf, sizeof(bf)); + pr_debug("bpf: load objects with prologue failed: err=%d: (%s)\n", + -errno, bf); + return -errno; + } + priv->prologue_fds[i] = fd; + } + /* + * We no longer need the original program, + * we can unload it. + */ + bpf_program__unload(prog); + } + return 0; +} + int bpf__load(struct bpf_object *obj) { int err; @@ -881,7 +1030,7 @@ int bpf__load(struct bpf_object *obj) pr_debug("bpf: load objects failed: err=%d: (%s)\n", err, bf); return err; } - return 0; + return bpf_object__load_prologue(obj); } int bpf__foreach_event(struct bpf_object *obj, @@ -916,13 +1065,10 @@ int bpf__foreach_event(struct bpf_object *obj, for (i = 0; i < pev->ntevs; i++) { tev = &pev->tevs[i]; - if (priv->need_prologue) { - int type = priv->type_mapping[i]; - - fd = bpf_program__nth_fd(prog, type); - } else { + if (priv->need_prologue) + fd = priv->prologue_fds[i]; + else fd = bpf_program__fd(prog); - } if (fd < 0) { pr_debug("bpf: failed to get file descriptor\n"); -- 2.7.4