[PATCH bpf-next 2/4] selftests/bpf: utility function to get program disassembly after jit

Eduard Zingerman
2024-08-09T01:05:51Z

int get_jited_program_text(int fd, char *text, size_t text_sz)

Loads and disassembles jited instructions for program pointed to by fd.
Much like 'bpftool prog dump jited ...'.

The code and makefile changes are inspired by jit_disasm.c from bpftool.
Use llvm libraries to disassemble BPF program instead of libbfd to avoid
issues with disassembly output stability pointed out in [1].

Selftests makefile uses Makefile.feature to detect if LLVM libraries
are available. If that is not the case selftests build proceeds but
the function returns -ENOTSUP at runtime.

[1] commit eb9d1acf634b ("bpftool: Add LLVM as default library for disassembling JIT-ed programs")

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
tools/testing/selftests/bpf/.gitignore | 1 +
tools/testing/selftests/bpf/Makefile | 51 +++-
.../selftests/bpf/jit_disasm_helpers.c | 228 ++++++++++++++++++
.../selftests/bpf/jit_disasm_helpers.h | 10 +
4 files changed, 288 insertions(+), 2 deletions(-)
create mode 100644 tools/testing/selftests/bpf/jit_disasm_helpers.c
create mode 100644 tools/testing/selftests/bpf/jit_disasm_helpers.h

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 8f14d8faeb0b..7de4108771a0 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -8,6 +8,7 @@ test_lru_map
test_lpm_map
test_tag
FEATURE-DUMP.libbpf
+FEATURE-DUMP.selftests
fixdep
/test_progs
/test_progs-no_alu32
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index f54185e96a95..b1a52739d9e7 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -33,6 +33,13 @@ OPT_FLAGS ?= $(if $(RELEASE),-O2,-O0)
LIBELF_CFLAGS := $(shell $(PKG_CONFIG) libelf --cflags 2>/dev/null)
LIBELF_LIBS := $(shell $(PKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)

+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
CFLAGS += -g $(OPT_FLAGS) -rdynamic \
-Wall -Werror -fno-omit-frame-pointer \
$(GENFLAGS) $(SAN_CFLAGS) $(LIBELF_CFLAGS) \
@@ -55,6 +62,11 @@ progs/test_sk_lookup.c-CFLAGS := -fno-strict-aliasing
progs/timer_crash.c-CFLAGS := -fno-strict-aliasing
progs/test_global_func9.c-CFLAGS := -fno-strict-aliasing

+# Some utility functions use LLVM libraries
+jit_disasm_helpers.c-CFLAGS = $(LLVM_CFLAGS)
+test_progs-LDLIBS = $(LLVM_LDLIBS)
+test_progs-LDFLAGS = $(LLVM_LDFLAGS)
+
ifneq ($(LLVM),)
# Silence some warnings when compiled with clang
CFLAGS += -Wno-unused-command-line-argument
@@ -164,6 +176,31 @@ endef

include ../lib.mk

+NON_CHECK_FEAT_TARGETS := clean docs-clean
+CHECK_FEAT := $(filter-out $(NON_CHECK_FEAT_TARGETS),$(or $(MAKECMDGOALS), "none"))
+ifneq ($(CHECK_FEAT),)
+FEATURE_USER := .selftests
+FEATURE_TESTS := llvm
+FEATURE_DISPLAY := $(FEATURE_TESTS)
+
+# Makefile.feature expects OUTPUT to end with a slash
+$(let OUTPUT,$(OUTPUT)/,\
+ $(eval include ../../../build/Makefile.feature))
+endif
+
+ifeq ($(feature-llvm),1)
+ LLVM_CFLAGS += -DHAVE_LLVM_SUPPORT
+ LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
+ # both llvm-config and lib.mk add -D_GNU_SOURCE, which ends up as conflict
+ LLVM_CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
+ LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
+ ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
+ LLVM_LDLIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
+ LLVM_LDLIBS += -lstdc++
+ endif
+ LLVM_LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
+endif
+
SCRATCH_DIR := $(OUTPUT)/tools
BUILD_DIR := $(SCRATCH_DIR)/build
INCLUDE_DIR := $(SCRATCH_DIR)/include
@@ -488,6 +525,7 @@ define DEFINE_TEST_RUNNER

TRUNNER_OUTPUT := $(OUTPUT)$(if $2,/)$2
TRUNNER_BINARY := $1$(if $2,-)$2
+TRUNNER_BASE_NAME := $1
TRUNNER_TEST_OBJS := $$(patsubst %.c,$$(TRUNNER_OUTPUT)/%.test.o, \
$$(notdir $$(wildcard $(TRUNNER_TESTS_DIR)/*.c)))
TRUNNER_EXTRA_OBJS := $$(patsubst %.c,$$(TRUNNER_OUTPUT)/%.o, \
@@ -611,6 +649,10 @@ ifeq ($(filter clean docs-clean,$(MAKECMDGOALS)),)
include $(wildcard $(TRUNNER_TEST_OBJS:.o=.d))
endif

+# add per extra obj CFGLAGS definitions
+$(foreach N,$(patsubst $(TRUNNER_OUTPUT)/%.o,%,$(TRUNNER_EXTRA_OBJS)), \
+ $(eval $(TRUNNER_OUTPUT)/$(N).o: CFLAGS += $($(N).c-CFLAGS)))
+
$(TRUNNER_EXTRA_OBJS): $(TRUNNER_OUTPUT)/%.o: \
%.c \
$(TRUNNER_EXTRA_HDRS) \
@@ -627,6 +669,9 @@ ifneq ($2:$(OUTPUT),:$(shell pwd))
$(Q)rsync -aq $$^ $(TRUNNER_OUTPUT)/
endif

+$(OUTPUT)/$(TRUNNER_BINARY): LDLIBS += $$($(TRUNNER_BASE_NAME)-LDLIBS)
+$(OUTPUT)/$(TRUNNER_BINARY): LDFLAGS += $$($(TRUNNER_BASE_NAME)-LDFLAGS)
+
# some X.test.o files have runtime dependencies on Y.bpf.o files
$(OUTPUT)/$(TRUNNER_BINARY): | $(TRUNNER_BPF_OBJS)

@@ -636,7 +681,7 @@ $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS) \
$(TRUNNER_BPFTOOL) \
| $(TRUNNER_BINARY)-extras
$$(call msg,BINARY,,$$@)
- $(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
+ $(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) $$(LDFLAGS) -o $$@
$(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@
$(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/$(USE_BOOTSTRAP)bpftool \
$(OUTPUT)/$(if $2,$2/)bpftool
@@ -655,6 +700,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c \
cap_helpers.c \
unpriv_helpers.c \
netlink_helpers.c \
+ jit_disasm_helpers.c \
test_loader.c \
xsk.c \
disasm.c \
@@ -797,7 +843,8 @@ EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR) \
$(addprefix $(OUTPUT)/,*.o *.d *.skel.h *.lskel.h *.subskel.h \
no_alu32 cpuv4 bpf_gcc bpf_testmod.ko \
bpf_test_no_cfi.ko \
- liburandom_read.so)
+ liburandom_read.so) \
+ $(OUTPUT)/FEATURE-DUMP.selftests

.PHONY: docs docs-clean

diff --git a/tools/testing/selftests/bpf/jit_disasm_helpers.c b/tools/testing/selftests/bpf/jit_disasm_helpers.c
new file mode 100644
index 000000000000..ae704f7c5ee7
--- /dev/null
+++ b/tools/testing/selftests/bpf/jit_disasm_helpers.c
@@ -0,0 +1,228 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+#include <test_progs.h>
+
+#ifdef HAVE_LLVM_SUPPORT
+
+#include <llvm-c/Core.h>
+#include <llvm-c/Disassembler.h>
+#include <llvm-c/Target.h>
+#include <llvm-c/TargetMachine.h>
+
+#define MAX_LOCAL_LABELS 32
+
+static bool llvm_initialized;
+
+struct local_labels {
+ bool print_phase;
+ __u32 prog_len;
+ __u32 cnt;
+ __u32 pcs[MAX_LOCAL_LABELS];
+ char names[MAX_LOCAL_LABELS][4];
+};
+
+/* Depending on labels->print_phase:
+ * - if false: record save jump labels within the program in labels->pcs;
+ * - if true: if ref_value is in labels->pcs, return corresponding labels->name.
+ */
+static const char *lookup_symbol(void *data, uint64_t ref_value, uint64_t *ref_type,
+ uint64_t ref_pc, const char **ref_name)
+{
+ struct local_labels *labels = data;
+ uint64_t type = *ref_type;
+ int i;
+
+ *ref_type = LLVMDisassembler_ReferenceType_InOut_None;
+ *ref_name = NULL;
+ if (type != LLVMDisassembler_ReferenceType_In_Branch)
+ return NULL;
+ for (i = 0; i < labels->cnt; ++i)
+ if (labels->pcs[i] == ref_value)
+ return labels->names[i];
+ if (!labels->print_phase && labels->cnt < MAX_LOCAL_LABELS &&
+ ref_value < labels->prog_len)
+ labels->pcs[labels->cnt++] = ref_value;
+ return NULL;
+}
+
+static int disasm_insn(LLVMDisasmContextRef ctx, uint8_t *image, __u32 len, __u32 pc,
+ char *buf, __u32 buf_sz)
+{
+ int i, cnt;
+
+ cnt = LLVMDisasmInstruction(ctx, image + pc, len - pc, pc,
+ buf, buf_sz);
+ if (cnt > 0)
+ return cnt;
+ PRINT_FAIL("Can't disasm instruction at offset %d:", pc);
+ for (i = 0; i < 16 && pc + i < len; ++i)
+ printf(" %02x", image[pc + i]);
+ printf("\n");
+ return -EINVAL;
+}
+
+static int cmp_u32(const void *_a, const void *_b)
+{
+ __u32 a = *(__u32 *)_a;
+ __u32 b = *(__u32 *)_b;
+
+ if (a < b)
+ return -1;
+ if (a > b)
+ return 1;
+ return 0;
+}
+
+static int disasm_one_func(FILE *text_out, uint8_t *image, __u32 len)
+{
+ char *label, *colon, *triple = NULL;
+ LLVMDisasmContextRef ctx = NULL;
+ struct local_labels labels = {};
+ __u32 *label_pc, pc;
+ int i, cnt, err = 0;
+ char buf[256];
+
+ triple = LLVMGetDefaultTargetTriple();
+ ctx = LLVMCreateDisasm(triple, &labels, 0, NULL, lookup_symbol);
+ if (!ASSERT_OK_PTR(ctx, "LLVMCreateDisasm")) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ cnt = LLVMSetDisasmOptions(ctx, LLVMDisassembler_Option_PrintImmHex);
+ if (!ASSERT_EQ(cnt, 1, "LLVMSetDisasmOptions")) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ /* discover labels */
+ labels.prog_len = len;
+ pc = 0;
+ while (pc < len) {
+ cnt = disasm_insn(ctx, image, len, pc, buf, 1);
+ if (cnt < 0) {
+ err = cnt;
+ goto out;
+ }
+ pc += cnt;
+ }
+ qsort(labels.pcs, labels.cnt, sizeof(*labels.pcs), cmp_u32);
+ /* GCC can't figure max bound for i and thus reports possible truncation */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-truncation"
+ for (i = 0; i < labels.cnt; ++i)
+ snprintf(labels.names[i], sizeof(labels.names[i]), "L%d", i);
+#pragma GCC diagnostic pop
+
+ /* now print with labels */
+ labels.print_phase = true;
+ pc = 0;
+ while (pc < len) {
+ cnt = disasm_insn(ctx, image, len, pc, buf, sizeof(buf));
+ if (cnt < 0) {
+ err = cnt;
+ goto out;
+ }
+ label_pc = bsearch(&pc, labels.pcs, labels.cnt, sizeof(*labels.pcs), cmp_u32);
+ label = "";
+ colon = "";
+ if (label_pc) {
+ label = labels.names[label_pc - labels.pcs];
+ colon = ":";
+ }
+ fprintf(text_out, "%x:\t", pc);
+ for (i = 0; i < cnt; ++i)
+ fprintf(text_out, "%02x ", image[pc + i]);
+ for (i = cnt * 3; i < 12 * 3; ++i)
+ fputc(' ', text_out);
+ fprintf(text_out, "%s%s%s\n", label, colon, buf);
+ pc += cnt;
+ }
+
+out:
+ if (triple)
+ LLVMDisposeMessage(triple);
+ if (ctx)
+ LLVMDisasmDispose(ctx);
+ return err;
+}
+
+int get_jited_program_text(int fd, char *text, size_t text_sz)
+{
+ struct bpf_prog_info info = {};
+ __u32 info_len = sizeof(info);
+ __u32 jited_funcs, len, pc;
+ __u32 *func_lens = NULL;
+ FILE *text_out = NULL;
+ uint8_t *image = NULL;
+ int i, err = 0;
+
+ if (!llvm_initialized) {
+ LLVMInitializeAllTargetInfos();
+ LLVMInitializeAllTargetMCs();
+ LLVMInitializeAllDisassemblers();
+ llvm_initialized = 1;
+ }
+
+ text_out = fmemopen(text, text_sz, "w");
+ if (!ASSERT_OK_PTR(text_out, "open_memstream")) {
+ err = -errno;
+ goto out;
+ }
+
+ /* first call is to find out jited program len */
+ err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
+ if (!ASSERT_OK(err, "bpf_prog_get_info_by_fd #1"))
+ goto out;
+
+ len = info.jited_prog_len;
+ image = malloc(len);
+ if (!ASSERT_OK_PTR(image, "malloc(info.jited_prog_len)")) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ jited_funcs = info.nr_jited_func_lens;
+ func_lens = malloc(jited_funcs * sizeof(__u32));
+ if (!ASSERT_OK_PTR(func_lens, "malloc(info.nr_jited_func_lens)")) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ memset(&info, 0, sizeof(info));
+ info.jited_prog_insns = (__u64)image;
+ info.jited_prog_len = len;
+ info.jited_func_lens = (__u64)func_lens;
+ info.nr_jited_func_lens = jited_funcs;
+ err = bpf_prog_get_info_by_fd(fd, &info, &info_len);
+ if (!ASSERT_OK(err, "bpf_prog_get_info_by_fd #2"))
+ goto out;
+
+ for (pc = 0, i = 0; i < jited_funcs; ++i) {
+ fprintf(text_out, "func #%d:\n", i);
+ disasm_one_func(text_out, image + pc, func_lens[i]);
+ fprintf(text_out, "\n");
+ pc += func_lens[i];
+ }
+
+out:
+ if (text_out)
+ fclose(text_out);
+ if (image)
+ free(image);
+ if (func_lens)
+ free(func_lens);
+ return err;
+}
+
+#else /* HAVE_LLVM_SUPPORT */
+
+int get_jited_program_text(int fd, char *text, size_t text_sz)
+{
+ if (env.verbosity >= VERBOSE_VERY)
+ printf("compiled w/o llvm development libraries, can't dis-assembly binary code");
+ return -ENOTSUP;
+}
+
+#endif /* HAVE_LLVM_SUPPORT */
diff --git a/tools/testing/selftests/bpf/jit_disasm_helpers.h b/tools/testing/selftests/bpf/jit_disasm_helpers.h
new file mode 100644
index 000000000000..e6924fd65ecf
--- /dev/null
+++ b/tools/testing/selftests/bpf/jit_disasm_helpers.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+#ifndef __JIT_DISASM_HELPERS_H
+#define __JIT_DISASM_HELPERS_H
+
+#include <stddef.h>
+
+int get_jited_program_text(int fd, char *text, size_t text_sz);
+
+#endif /* __JIT_DISASM_HELPERS_H */
--
2.45.2