netdev - [RFC PATCH bpf-next 2/7] libbpf: add per-file linker opts

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Date:   Thu, 6 May 2021 22:41:14 -0700
From:   Andrii Nakryiko <andrii@...nel.org>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii@...nel.org>, <kernel-team@...com>
Subject: [RFC PATCH bpf-next 2/7] libbpf: add per-file linker opts

For better future extensibility add per-file linker options. Currently
the set of available options is empty. This changes bpf_linker__add_file()
API, but it's not a breaking change as bpf_linker APIs hasn't been released
yet.

Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 tools/bpf/bpftool/gen.c |  2 +-
 tools/lib/bpf/libbpf.h  | 10 +++++++++-
 tools/lib/bpf/linker.c  | 16 ++++++++++++----
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 440a2fcb6441..06fee4a2910a 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -638,7 +638,7 @@ static int do_object(int argc, char **argv)
 	while (argc) {
 		file = GET_ARG();
 
-		err = bpf_linker__add_file(linker, file);
+		err = bpf_linker__add_file(linker, file, NULL);
 		if (err) {
 			p_err("failed to link '%s': %s (%d)", file, strerror(err), err);
 			goto out;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index bec4e6a6e31d..3f3a24763459 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -768,10 +768,18 @@ struct bpf_linker_opts {
 };
 #define bpf_linker_opts__last_field sz
 
+struct bpf_linker_file_opts {
+	/* size of this struct, for forward/backward compatiblity */
+	size_t sz;
+};
+#define bpf_linker_file_opts__last_field sz
+
 struct bpf_linker;
 
 LIBBPF_API struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts);
-LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filename);
+LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker,
+				    const char *filename,
+				    const struct bpf_linker_file_opts *opts);
 LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
 LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);
 
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 9de084b1c699..3b1fbc27be37 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -158,7 +158,9 @@ struct bpf_linker {
 
 static int init_output_elf(struct bpf_linker *linker, const char *file);
 
-static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, struct src_obj *obj);
+static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
+				const struct bpf_linker_file_opts *opts,
+				struct src_obj *obj);
 static int linker_sanity_check_elf(struct src_obj *obj);
 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
@@ -435,15 +437,19 @@ static int init_output_elf(struct bpf_linker *linker, const char *file)
 	return 0;
 }
 
-int bpf_linker__add_file(struct bpf_linker *linker, const char *filename)
+int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
+			 const struct bpf_linker_file_opts *opts)
 {
 	struct src_obj obj = {};
 	int err = 0;
 
+	if (!OPTS_VALID(opts, bpf_linker_file_opts))
+		return -EINVAL;
+
 	if (!linker->elf)
 		return -EINVAL;
 
-	err = err ?: linker_load_obj_file(linker, filename, &obj);
+	err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
 	err = err ?: linker_append_sec_data(linker, &obj);
 	err = err ?: linker_append_elf_syms(linker, &obj);
 	err = err ?: linker_append_elf_relos(linker, &obj);
@@ -529,7 +535,9 @@ static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
 	return sec;
 }
 
-static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, struct src_obj *obj)
+static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
+				const struct bpf_linker_file_opts *opts,
+				struct src_obj *obj)
 {
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 	const int host_endianness = ELFDATA2LSB;
-- 
2.30.2