[PATCH bpf-next 2/2] tools/bpf/bpftool: xlated dump from ELF file directly

[Lorenzo Fontana <fontanalorenz@gmail.com>]

bpftool can dump an xlated or jitted representation
of the programs already loaded into the kernel.
That capability is very useful for understanding what
are the instructions the kernel will execute for that program.

However, sometimes the verifier does not load the program and
one cannot use this feature until changes are made to make the
verifier happy again.

This patch reuses the same dump function to dump the program
from an ELF file directly instead of loading the instructions
from a loaded file descriptor. In this way, the user
can use all the bpftool features for "xlated" without loading.

In particular, the "visual" command is very useful when combined
to this because the dot graph makes easy to spot bad instruction
sequences.

Usage:

  bpftool prog dump xlated elf program.o

It also works with the other commands like 'visual' to print
an dot representation of the program.

  bpftool prog dump xlated elf program.o visual

Signed-off-by: Lorenzo Fontana <fontanalorenz@gmail.com>
---
 tools/bpf/bpftool/common.c | 15 ++++++++++++---
 tools/bpf/bpftool/main.h   |  2 +-
 tools/bpf/bpftool/prog.c   | 26 +++++++++++++++++++++++---
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index 1828bba19020..b28d15505705 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -703,7 +703,7 @@ static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
 	return -1;
 }
 
-int prog_parse_fds(int *argc, char ***argv, int **fds)
+int prog_parse_fds(int *argc, char ***argv, int **fds, char **elf_filepath)
 {
 	if (is_prefix(**argv, "id")) {
 		unsigned int id;
@@ -763,9 +763,18 @@ int prog_parse_fds(int *argc, char ***argv, int **fds)
 		if ((*fds)[0] < 0)
 			return -1;
 		return 1;
+	} else if (is_prefix(**argv, "elf")) {
+		NEXT_ARGP();
+		if (!argc) {
+			p_err("expected ELF file path");
+			return -1;
+		}
+		*elf_filepath = **argv;
+		NEXT_ARGP();
+		return 1;
 	}
 
-	p_err("expected 'id', 'tag', 'name' or 'pinned', got: '%s'?", **argv);
+	p_err("expected 'id', 'tag', 'name', 'elf' or 'pinned', got: '%s'?", **argv);
 	return -1;
 }
 
@@ -779,7 +788,7 @@ int prog_parse_fd(int *argc, char ***argv)
 		p_err("mem alloc failed");
 		return -1;
 	}
-	nb_fds = prog_parse_fds(argc, argv, &fds);
+	nb_fds = prog_parse_fds(argc, argv, &fds, NULL);
 	if (nb_fds != 1) {
 		if (nb_fds > 1) {
 			p_err("several programs match this handle");
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index c1cf29798b99..f4e426d03b4a 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -187,7 +187,7 @@ int do_iter(int argc, char **argv) __weak;
 
 int parse_u32_arg(int *argc, char ***argv, __u32 *val, const char *what);
 int prog_parse_fd(int *argc, char ***argv);
-int prog_parse_fds(int *argc, char ***argv, int **fds);
+int prog_parse_fds(int *argc, char ***argv, int **fds, char **elf_filepath);
 int map_parse_fd(int *argc, char ***argv);
 int map_parse_fds(int *argc, char ***argv, int **fds);
 int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len);
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index cc48726740ad..04fa9a83ef7e 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -537,7 +537,7 @@ static int do_show_subset(int argc, char **argv)
 		p_err("mem alloc failed");
 		return -1;
 	}
-	nb_fds = prog_parse_fds(&argc, &argv, &fds);
+	nb_fds = prog_parse_fds(&argc, &argv, &fds, NULL);
 	if (nb_fds < 1)
 		goto exit_free;
 
@@ -787,7 +787,10 @@ prog_dump(struct bpf_prog_info *info, enum dump_mode mode,
 static int do_dump(int argc, char **argv)
 {
 	struct bpf_prog_info_linear *info_linear;
+	struct bpf_object *obj;
+	struct bpf_program *prog;
 	char *filepath = NULL;
+	char *elf_filepath = NULL;
 	bool opcodes = false;
 	bool visual = false;
 	enum dump_mode mode;
@@ -817,7 +820,8 @@ static int do_dump(int argc, char **argv)
 		p_err("mem alloc failed");
 		return -1;
 	}
-	nb_fds = prog_parse_fds(&argc, &argv, &fds);
+	elf_filepath = malloc(sizeof(char) * PATH_MAX);
+	nb_fds = prog_parse_fds(&argc, &argv, &fds, &elf_filepath);
 	if (nb_fds < 1)
 		goto exit_free;
 
@@ -849,7 +853,6 @@ static int do_dump(int argc, char **argv)
 		linum = true;
 		NEXT_ARG();
 	}
-
 	if (argc) {
 		usage();
 		goto exit_close;
@@ -866,9 +869,26 @@ static int do_dump(int argc, char **argv)
 	arrays |= 1UL << BPF_PROG_INFO_LINE_INFO;
 	arrays |= 1UL << BPF_PROG_INFO_JITED_LINE_INFO;
 
+	if (elf_filepath != NULL) {
+		obj = bpf_object__open(elf_filepath); 
+		if (libbpf_get_error(obj)) {
+			p_err("ERROR: opening BPF object file failed");
+			return 0;
+		}
+
+		bpf_object__for_each_program(prog, obj) {
+			struct bpf_prog_info pinfo;
+			pinfo.xlated_prog_insns = ptr_to_u64(bpf_program__insns(prog));
+			pinfo.xlated_prog_len = bpf_program__size(prog);
+			err = prog_dump(&pinfo, mode, filepath, opcodes, visual, linum);
+		}
+		return 0;
+	}
+
 	if (json_output && nb_fds > 1)
 		jsonw_start_array(json_wtr);	/* root array */
 	for (i = 0; i < nb_fds; i++) {
+		printf("uno\n");
 		info_linear = bpf_program__get_prog_info_linear(fds[i], arrays);
 		if (IS_ERR_OR_NULL(info_linear)) {
 			p_err("can't get prog info: %s", strerror(errno));
-- 
2.32.0