[RFC bpf-next v1 4/8] selftests/bpf: extract utility function for BPF disassembly

Eduard Zingerman
2024-06-29T09:48:10Z

uint32_t disasm_insn(struct bpf_insn *insn, char *buf, size_t buf_sz);

Disassembles instruction 'insn' to a text buffer 'buf'.
Removes insn->code hex prefix added by kernel disassemly routine.
Returns the length of decoded instruction (either 1 or 2).

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
tools/testing/selftests/bpf/Makefile | 1 +
tools/testing/selftests/bpf/disasm_helpers.c | 50 +++++++++++++
tools/testing/selftests/bpf/disasm_helpers.h | 12 ++++
.../selftests/bpf/prog_tests/ctx_rewrite.c | 71 +++----------------
tools/testing/selftests/bpf/testing_helpers.c | 1 +
5 files changed, 72 insertions(+), 63 deletions(-)
create mode 100644 tools/testing/selftests/bpf/disasm_helpers.c
create mode 100644 tools/testing/selftests/bpf/disasm_helpers.h

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index e0b3887b3d2d..5eb7b5eb89d2 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -636,6 +636,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c \
test_loader.c \
xsk.c \
disasm.c \
+ disasm_helpers.c \
json_writer.c \
flow_dissector_load.h \
ip_check_defrag_frags.h
diff --git a/tools/testing/selftests/bpf/disasm_helpers.c b/tools/testing/selftests/bpf/disasm_helpers.c
new file mode 100644
index 000000000000..7c29d294a456
--- /dev/null
+++ b/tools/testing/selftests/bpf/disasm_helpers.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+
+#include <bpf/bpf.h>
+#include "disasm.h"
+
+struct print_insn_context {
+ char *buf;
+ size_t sz;
+};
+
+static void print_insn_cb(void *private_data, const char *fmt, ...)
+{
+ struct print_insn_context *ctx = private_data;
+ va_list args;
+
+ va_start(args, fmt);
+ vsnprintf(ctx->buf, ctx->sz, fmt, args);
+ va_end(args);
+}
+
+uint32_t disasm_insn(struct bpf_insn *insn, char *buf, size_t buf_sz)
+{
+ struct print_insn_context ctx = {
+ .buf = buf,
+ .sz = buf_sz,
+ };
+ struct bpf_insn_cbs cbs = {
+ .cb_print = print_insn_cb,
+ .private_data = &ctx,
+ };
+ int pfx_end, sfx_start, len;
+ bool double_insn;
+
+ print_bpf_insn(&cbs, insn, true);
+ /* We share code with kernel BPF disassembler, it adds '(FF) ' prefix
+ * for each instruction (FF stands for instruction `code` byte).
+ * Remove the prefix inplace, and also simplify call instructions.
+ * E.g.: "(85) call foo#10" -> "call foo".
+ */
+ pfx_end = 0;
+ sfx_start = max((int)strlen(buf) - 1, 0);
+ /* For whatever reason %n is not counted in sscanf return value */
+ sscanf(buf, "(%*[^)]) %n", &pfx_end);
+ sscanf(buf, "(%*[^)]) call %*[^#]%n", &sfx_start);
+ len = sfx_start - pfx_end;
+ memmove(buf, buf + pfx_end, len);
+ buf[len] = 0;
+ double_insn = insn->code == (BPF_LD | BPF_IMM | BPF_DW);
+ return double_insn ? 2 : 1;
+}
diff --git a/tools/testing/selftests/bpf/disasm_helpers.h b/tools/testing/selftests/bpf/disasm_helpers.h
new file mode 100644
index 000000000000..db3dfe9f93dd
--- /dev/null
+++ b/tools/testing/selftests/bpf/disasm_helpers.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+
+#ifndef __DISASM_HELPERS_H
+#define __DISASM_HELPERS_H
+
+#include <stdlib.h>
+
+struct bpf_insn;
+
+uint32_t disasm_insn(struct bpf_insn *insn, char *buf, size_t buf_sz);
+
+#endif /* __DISASM_HELPERS_H */
diff --git a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
index 08b6391f2f56..55e41167f1f3 100644
--- a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
+++ b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
@@ -10,7 +10,8 @@
#include "bpf/btf.h"
#include "bpf_util.h"
#include "linux/filter.h"
-#include "disasm.h"
+#include "linux/kernel.h"
+#include "disasm_helpers.h"

#define MAX_PROG_TEXT_SZ (32 * 1024)

@@ -628,63 +629,6 @@ static bool match_pattern(struct btf *btf, char *pattern, char *text, char *reg_
return false;
}

-static void print_insn(void *private_data, const char *fmt, ...)
-{
- va_list args;
-
- va_start(args, fmt);
- vfprintf((FILE *)private_data, fmt, args);
- va_end(args);
-}
-
-/* Disassemble instructions to a stream */
-static void print_xlated(FILE *out, struct bpf_insn *insn, __u32 len)
-{
- const struct bpf_insn_cbs cbs = {
- .cb_print = print_insn,
- .cb_call = NULL,
- .cb_imm = NULL,
- .private_data = out,
- };
- bool double_insn = false;
- int i;
-
- for (i = 0; i < len; i++) {
- if (double_insn) {
- double_insn = false;
- continue;
- }
-
- double_insn = insn[i].code == (BPF_LD | BPF_IMM | BPF_DW);
- print_bpf_insn(&cbs, insn + i, true);
- }
-}
-
-/* We share code with kernel BPF disassembler, it adds '(FF) ' prefix
- * for each instruction (FF stands for instruction `code` byte).
- * This function removes the prefix inplace for each line in `str`.
- */
-static void remove_insn_prefix(char *str, int size)
-{
- const int prefix_size = 5;
-
- int write_pos = 0, read_pos = prefix_size;
- int len = strlen(str);
- char c;
-
- size = min(size, len);
-
- while (read_pos < size) {
- c = str[read_pos++];
- if (c == 0)
- break;
- str[write_pos++] = c;
- if (c == '\n')
- read_pos += prefix_size;
- }
- str[write_pos] = 0;
-}
-
struct prog_info {
char *prog_kind;
enum bpf_prog_type prog_type;
@@ -702,8 +646,10 @@ static void match_program(struct btf *btf,
struct bpf_insn *buf = NULL;
int err = 0, prog_fd = 0;
FILE *prog_out = NULL;
+ char insn_buf[64];
char *text = NULL;
__u32 cnt = 0;
+ int i;

text = calloc(MAX_PROG_TEXT_SZ, 1);
if (!text) {
@@ -739,12 +685,11 @@ static void match_program(struct btf *btf,
PRINT_FAIL("Can't open memory stream\n");
goto out;
}
- if (skip_first_insn)
- print_xlated(prog_out, buf + 1, cnt - 1);
- else
- print_xlated(prog_out, buf, cnt);
+ for (i = skip_first_insn ? 1 : 0; i < cnt;) {
+ i += disasm_insn(buf + i, insn_buf, sizeof(insn_buf));
+ fprintf(prog_out, "%s\n", insn_buf);
+ }
fclose(prog_out);
- remove_insn_prefix(text, MAX_PROG_TEXT_SZ);

ASSERT_TRUE(match_pattern(btf, pattern, text, reg_map),
pinfo->prog_kind);
diff --git a/tools/testing/selftests/bpf/testing_helpers.c b/tools/testing/selftests/bpf/testing_helpers.c
index d5379a0e6da8..ac7c66f4fc7b 100644
--- a/tools/testing/selftests/bpf/testing_helpers.c
+++ b/tools/testing/selftests/bpf/testing_helpers.c
@@ -7,6 +7,7 @@
#include <errno.h>
#include <bpf/bpf.h>
#include <bpf/libbpf.h>
+#include "disasm.h"
#include "test_progs.h"
#include "testing_helpers.h"
#include <linux/membarrier.h>
--
2.45.2