[PATCH bpf-next 07/10] bpftool: add `gen bpfo` command to perform BPF static linking

[Andrii Nakryiko <andrii@xxxxxxxxxx>]

Add `bpftool gen bpfo <output-file> <input_file>...` command to statically
link multiple BPF object files into a single output BPF object file.

Similarly to existing '*.o' convention, bpftool is establishing a '*.bpfo'
convention for statically-linked BPF object files. Both .o and .bpfo suffixes
will be stripped out during BPF skeleton generation to infer BPF object name.

Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
 tools/bpf/bpftool/gen.c | 46 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 4033c46d83e7..8b1ed6c0a62f 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -54,7 +54,9 @@ static void get_obj_name(char *name, const char *file)
 	strncpy(name, basename(file), MAX_OBJ_NAME_LEN - 1);
 	name[MAX_OBJ_NAME_LEN - 1] = '\0';
 	if (str_has_suffix(name, ".o"))
-		name[strlen(name) - 2] = '\0';
+		name[strlen(name) - sizeof(".o") + 1] = '\0';
+	else if (str_has_suffix(name, ".bpfo"))
+		name[strlen(name) - sizeof(".bpfo") + 1] = '\0';
 	sanitize_identifier(name);
 }
 
@@ -591,6 +593,47 @@ static int do_skeleton(int argc, char **argv)
 	return err;
 }
 
+static int do_bpfo(int argc, char **argv)
+{
+	struct bpf_linker *linker;
+	const char *output_file, *file;
+	int err;
+
+	if (!REQ_ARGS(2)) {
+		usage();
+		return -1;
+	}
+
+	output_file = GET_ARG();
+
+	linker = bpf_linker__new(output_file, NULL);
+	if (!linker) {
+		p_err("failed to create BPF linker instance");
+		return -1;
+	}
+
+	while (argc) {
+		file = GET_ARG();
+
+		err = bpf_linker__add_file(linker, file);
+		if (err) {
+			p_err("failed to link '%s': %d", file, err);
+			goto err_out;
+		}
+	}
+
+	err = bpf_linker__finalize(linker);
+	if (err) {
+		p_err("failed to finalize ELF file: %d", err);
+		goto err_out;
+	}
+
+	return 0;
+err_out:
+	bpf_linker__free(linker);
+	return -1;
+}
+
 static int do_help(int argc, char **argv)
 {
 	if (json_output) {
@@ -611,6 +654,7 @@ static int do_help(int argc, char **argv)
 
 static const struct cmd cmds[] = {
 	{ "skeleton",	do_skeleton },
+	{ "bpfo",	do_bpfo },
 	{ "help",	do_help },
 	{ 0 }
 };
-- 
2.24.1