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Thu, 09 Apr 2026 18:12:01 -0700 (PDT) Received: from ezingerman-fedora-PF4V722J.thefacebook.com ([2620:10d:c090:500::2:f3a8]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2d5627c44fcsm2174922eec.23.2026.04.09.18.11.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 18:12:00 -0700 (PDT) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org Cc: daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, eddyz87@gmail.com Subject: [PATCH bpf-next v2 09/13] bpf: change logging scheme for live stack analysis Date: Thu, 9 Apr 2026 18:11:28 -0700 Message-ID: <20260409-patch-set-v2-9-651804512349@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260409-patch-set-v2-0-651804512349@gmail.com> References: <20260409-patch-set-v2-0-651804512349@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Instead of breadcrumps like: (d2,cs15) frame 0 insn 18 +live -16 (d2,cs15) frame 0 insn 17 +live -16 Print final accumulated stack use/def data per-func_instance per-instruction. printed func_instance's are ordered by callsite and depth. For example: stack use/def subprog#0 shared_instance_must_write_overwrite (d0,cs0): 0: (b7) r1 = 1 1: (7b) *(u64 *)(r10 -8) = r1 ; def: fp0-8 2: (7b) *(u64 *)(r10 -16) = r1 ; def: fp0-16 3: (bf) r1 = r10 4: (07) r1 += -8 5: (bf) r2 = r10 6: (07) r2 += -16 7: (85) call pc+7 ; use: fp0-8 fp0-16 8: (bf) r1 = r10 9: (07) r1 += -16 10: (bf) r2 = r10 11: (07) r2 += -8 12: (85) call pc+2 ; use: fp0-8 fp0-16 13: (b7) r0 = 0 14: (95) exit stack use/def subprog#1 forwarding_rw (d1,cs7): 15: (85) call pc+1 ; use: fp0-8 fp0-16 16: (95) exit stack use/def subprog#1 forwarding_rw (d1,cs12): 15: (85) call pc+1 ; use: fp0-8 fp0-16 16: (95) exit stack use/def subprog#2 write_first_read_second (d2,cs15): 17: (7a) *(u64 *)(r1 +0) = 42 18: (79) r0 = *(u64 *)(r2 +0) ; use: fp0-8 fp0-16 19: (95) exit For groups of three or more consecutive stack slots, abbreviate as follows: 25: (85) call bpf_loop#181 ; use: fp2-8..-512 fp1-8..-512 fp0-8..-512 Signed-off-by: Eduard Zingerman --- include/linux/bpf_verifier.h | 5 - kernel/bpf/liveness.c | 238 +++++++++++++++++++++++++++++-------------- 2 files changed, 162 insertions(+), 81 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 1ee94e36806d..5d6c6d1f46ed 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -256,11 +256,6 @@ static inline spis_t spis_and(spis_t a, spis_t b) return (spis_t){{ a.v[0] & b.v[0], a.v[1] & b.v[1] }}; } -static inline spis_t spis_xor(spis_t a, spis_t b) -{ - return (spis_t){{ a.v[0] ^ b.v[0], a.v[1] ^ b.v[1] }}; -} - static inline spis_t spis_not(spis_t s) { return (spis_t){{ ~s.v[0], ~s.v[1] }}; diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c index c13f57ddf582..f296c3304752 100644 --- a/kernel/bpf/liveness.c +++ b/kernel/bpf/liveness.c @@ -6,6 +6,7 @@ #include #include #include +#include #define verbose(env, fmt, args...) bpf_verifier_log_write(env, fmt, ##args) @@ -261,64 +262,6 @@ static int mark_stack_write(struct func_instance *instance, u32 frame, u32 insn_ return 0; } -static char *fmt_instance(struct bpf_verifier_env *env, struct func_instance *instance) -{ - snprintf(env->tmp_str_buf, sizeof(env->tmp_str_buf), - "(d%d,cs%d)", instance->depth, instance->callsite); - return env->tmp_str_buf; -} - -/* - * When both halves of an 8-byte SPI are set, print as "-8","-16",... - * When only one half is set, print as "-4h","-8h",... - */ -static void bpf_fmt_spis_mask(char *buf, ssize_t buf_sz, spis_t spis) -{ - bool first = true; - int spi, n; - - buf[0] = '\0'; - - for (spi = 0; spi < STACK_SLOTS / 2 && buf_sz > 0; spi++) { - bool lo = spis_test_bit(spis, spi * 2); - bool hi = spis_test_bit(spis, spi * 2 + 1); - - if (!lo && !hi) - continue; - n = snprintf(buf, buf_sz, "%s%d%s", - first ? "" : ",", - -(spi + 1) * BPF_REG_SIZE + (lo && !hi ? BPF_HALF_REG_SIZE : 0), - lo && hi ? "" : "h"); - first = false; - buf += n; - buf_sz -= n; - } -} - -static void log_mask_change(struct bpf_verifier_env *env, struct func_instance *instance, - char *pfx, u32 frame, u32 insn_idx, - spis_t old, spis_t new) -{ - spis_t changed_bits, new_ones, new_zeros; - - changed_bits = spis_xor(old, new); - new_ones = spis_and(new, changed_bits); - new_zeros = spis_and(spis_not(new), changed_bits); - - if (spis_is_zero(changed_bits)) - return; - bpf_log(&env->log, "%s frame %d insn %d ", fmt_instance(env, instance), frame, insn_idx); - if (!spis_is_zero(new_ones)) { - bpf_fmt_spis_mask(env->tmp_str_buf, sizeof(env->tmp_str_buf), new_ones); - bpf_log(&env->log, "+%s %s ", pfx, env->tmp_str_buf); - } - if (!spis_is_zero(new_zeros)) { - bpf_fmt_spis_mask(env->tmp_str_buf, sizeof(env->tmp_str_buf), new_zeros); - bpf_log(&env->log, "-%s %s", pfx, env->tmp_str_buf); - } - bpf_log(&env->log, "\n"); -} - int bpf_jmp_offset(struct bpf_insn *insn) { u8 code = insn->code; @@ -394,7 +337,6 @@ __diag_pop(); static inline bool update_insn(struct bpf_verifier_env *env, struct func_instance *instance, u32 frame, u32 insn_idx) { - struct bpf_insn_aux_data *aux = env->insn_aux_data; spis_t new_before, new_after; struct per_frame_masks *insn, *succ_insn; struct bpf_iarray *succ; @@ -421,13 +363,6 @@ static inline bool update_insn(struct bpf_verifier_env *env, new_before = spis_or(spis_and(new_after, spis_not(insn->must_write)), insn->may_read); changed |= !spis_equal(new_before, insn->live_before); - if (unlikely(env->log.level & BPF_LOG_LEVEL2) && - (!spis_is_zero(insn->may_read) || !spis_is_zero(insn->must_write) || - insn_idx == instance->subprog_start || - aux[insn_idx].prune_point)) { - log_mask_change(env, instance, "live", - frame, insn_idx, insn->live_before, new_before); - } insn->live_before = new_before; return changed; } @@ -457,10 +392,6 @@ static void update_instance(struct bpf_verifier_env *env, struct func_instance * changed |= update_insn(env, instance, frame, insn_postorder[i]); } } while (changed); - - if (env->log.level & BPF_LOG_LEVEL2) - bpf_log(&env->log, "%s live stack update done in %d iterations\n", - fmt_instance(env, instance), cnt); } static bool is_live_before(struct func_instance *instance, u32 insn_idx, u32 frameno, u32 half_spi) @@ -540,6 +471,163 @@ bool bpf_stack_slot_alive(struct bpf_verifier_env *env, u32 frameno, u32 half_sp return false; } +static char *fmt_subprog(struct bpf_verifier_env *env, int subprog) +{ + snprintf(env->tmp_str_buf, sizeof(env->tmp_str_buf), + "subprog#%d %s", subprog, env->subprog_info[subprog].name); + return env->tmp_str_buf; +} + +static char *fmt_instance(struct bpf_verifier_env *env, struct func_instance *instance) +{ + snprintf(env->tmp_str_buf, sizeof(env->tmp_str_buf), + "(d%d,cs%d)", instance->depth, instance->callsite); + return env->tmp_str_buf; +} + +static int spi_off(int spi) +{ + return -(spi + 1) * BPF_REG_SIZE; +} + +/* + * When both halves of an 8-byte SPI are set, print as "-8","-16",... + * When only one half is set, print as "-4h","-8h",... + * Runs of 3+ consecutive fully-set SPIs are collapsed: "fp0-8..-24" + */ +static char *fmt_spis_mask(struct bpf_verifier_env *env, int frame, bool first, spis_t spis) +{ + int buf_sz = sizeof(env->tmp_str_buf); + char *buf = env->tmp_str_buf; + int spi, n, run_start; + + buf[0] = '\0'; + + for (spi = 0; spi < STACK_SLOTS / 2 && buf_sz > 0; spi++) { + bool lo = spis_test_bit(spis, spi * 2); + bool hi = spis_test_bit(spis, spi * 2 + 1); + const char *space = first ? "" : " "; + + if (!lo && !hi) + continue; + + if (!lo || !hi) { + /* half-spi */ + n = snprintf(buf, buf_sz, "%sfp%d%d%s", + space, frame, spi_off(spi) + (lo ? STACK_SLOT_SZ : 0), "h"); + } else if (spi + 2 < STACK_SLOTS / 2 && + spis_test_bit(spis, spi * 2 + 2) && + spis_test_bit(spis, spi * 2 + 3) && + spis_test_bit(spis, spi * 2 + 4) && + spis_test_bit(spis, spi * 2 + 5)) { + /* 3+ consecutive full spis */ + run_start = spi; + while (spi + 1 < STACK_SLOTS / 2 && + spis_test_bit(spis, (spi + 1) * 2) && + spis_test_bit(spis, (spi + 1) * 2 + 1)) + spi++; + n = snprintf(buf, buf_sz, "%sfp%d%d..%d", + space, frame, spi_off(run_start), spi_off(spi)); + } else { + /* just a full spi */ + n = snprintf(buf, buf_sz, "%sfp%d%d", space, frame, spi_off(spi)); + } + first = false; + buf += n; + buf_sz -= n; + } + return env->tmp_str_buf; +} + +static void print_instance(struct bpf_verifier_env *env, struct func_instance *instance) +{ + int start = env->subprog_info[instance->subprog].start; + struct bpf_insn *insns = env->prog->insnsi; + struct per_frame_masks *masks; + int insn_idx, frame, pos, insn_pos, i; + int len = instance->insn_cnt; + bool has_use, has_def; + + if (!(env->log.level & BPF_LOG_LEVEL2)) + return; + + verbose(env, "stack use/def %s ", fmt_subprog(env, instance->subprog)); + verbose(env, "%s:\n", fmt_instance(env, instance)); + for (i = 0; i < len; i++) { + insn_idx = start + i; + has_use = false; + has_def = false; + pos = env->log.end_pos; + verbose(env, "%3d: ", insn_idx); + bpf_verbose_insn(env, &insns[insn_idx]); + bpf_vlog_reset(&env->log, env->log.end_pos - 1); /* remove \n */ + insn_pos = env->log.end_pos; + verbose(env, "%*c;", bpf_vlog_alignment(insn_pos - pos), ' '); + pos = env->log.end_pos; + verbose(env, " use: "); + for (frame = instance->depth; frame >= 0; --frame) { + masks = get_frame_masks(instance, frame, insn_idx); + if (!masks || spis_is_zero(masks->may_read)) + continue; + verbose(env, "%s", fmt_spis_mask(env, frame, !has_use, masks->may_read)); + has_use = true; + } + if (!has_use) + bpf_vlog_reset(&env->log, pos); + pos = env->log.end_pos; + verbose(env, " def: "); + for (frame = instance->depth; frame >= 0; --frame) { + masks = get_frame_masks(instance, frame, insn_idx); + if (!masks || spis_is_zero(masks->must_write)) + continue; + verbose(env, "%s", fmt_spis_mask(env, frame, !has_def, masks->must_write)); + has_def = true; + } + if (!has_def) + bpf_vlog_reset(&env->log, has_use ? pos : insn_pos); + verbose(env, "\n"); + if (bpf_is_ldimm64(&insns[insn_idx])) + i++; + } +} + +static int cmp_instances(const void *pa, const void *pb) +{ + struct func_instance *a = *(struct func_instance **)pa; + struct func_instance *b = *(struct func_instance **)pb; + int dcallsite = (int)a->callsite - b->callsite; + int ddepth = (int)a->depth - b->depth; + + if (dcallsite) + return dcallsite; + if (ddepth) + return ddepth; + return 0; +} + +/* print use/def slots for all instances ordered by callsite first, then by depth */ +static int print_instances(struct bpf_verifier_env *env) +{ + struct func_instance *instance, **sorted_instances; + struct bpf_liveness *liveness = env->liveness; + int i, bkt, cnt; + + cnt = 0; + hash_for_each(liveness->func_instances, bkt, instance, hl_node) + cnt++; + sorted_instances = kvmalloc_objs(*sorted_instances, cnt, GFP_KERNEL_ACCOUNT); + if (!sorted_instances) + return -ENOMEM; + cnt = 0; + hash_for_each(liveness->func_instances, bkt, instance, hl_node) + sorted_instances[cnt++] = instance; + sort(sorted_instances, cnt, sizeof(*sorted_instances), cmp_instances, NULL); + for (i = 0; i < cnt; i++) + print_instance(env, sorted_instances[i]); + kvfree(sorted_instances); + return 0; +} + /* * Per-register tracking state for compute_subprog_args(). * Tracks which frame's FP a value is derived from @@ -1430,12 +1518,7 @@ static void print_subprog_arg_access(struct bpf_verifier_env *env, if (!(env->log.level & BPF_LOG_LEVEL2)) return; - verbose(env, "subprog#%d %s:\n", subprog, - env->prog->aux->func_info - ? btf_name_by_offset(env->prog->aux->btf, - btf_type_by_id(env->prog->aux->btf, - env->prog->aux->func_info[subprog].type_id)->name_off) - : ""); + verbose(env, "%s:\n", fmt_subprog(env, subprog)); for (i = 0; i < len; i++) { int idx = start + i; bool has_extra = false; @@ -1821,6 +1904,9 @@ int bpf_compute_subprog_arg_access(struct bpf_verifier_env *env) goto out; } + if (env->log.level & BPF_LOG_LEVEL2) + err = print_instances(env); + out: for (k = 0; k < insn_cnt; k++) kvfree(env->callsite_at_stack[k]); -- 2.53.0