Commit e6c64855 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: add btf__parse_elf API to load .BTF and .BTF.ext 



Loading BTF and BTF.ext from ELF file is a common need. Instead of
requiring every user to re-implement it, let's provide this API from
libbpf itself. It's mostly copy/paste from `bpftool btf dump`
implementation, which will be switched to libbpf's version in next
patch. btf__parse_elf allows to load BTF and optionally BTF.ext.
This is also useful for tests that need to load/work with BTF, loaded
from test ELF files.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 1d7a08b3

tools/lib/bpf/btf.c

+128 −0
Original line number Diff line number Diff line
@@ -4,10 +4,12 @@ 
#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <fcntl.h>

#include <unistd.h>

#include <errno.h>

#include <linux/err.h>

#include <linux/btf.h>

#include <gelf.h>

#include "btf.h"

#include "bpf.h"

#include "libbpf.h"
@@ -417,6 +419,132 @@ done: 
	return btf;

}



static bool btf_check_endianness(const GElf_Ehdr *ehdr)

{

#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__

	return ehdr->e_ident[EI_DATA] == ELFDATA2LSB;

#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

	return ehdr->e_ident[EI_DATA] == ELFDATA2MSB;

#else

# error "Unrecognized __BYTE_ORDER__"

#endif

}



struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)

{

	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;

	int err = 0, fd = -1, idx = 0;

	struct btf *btf = NULL;

	Elf_Scn *scn = NULL;

	Elf *elf = NULL;

	GElf_Ehdr ehdr;



	if (elf_version(EV_CURRENT) == EV_NONE) {

		pr_warning("failed to init libelf for %s\n", path);

		return ERR_PTR(-LIBBPF_ERRNO__LIBELF);

	}



	fd = open(path, O_RDONLY);

	if (fd < 0) {

		err = -errno;

		pr_warning("failed to open %s: %s\n", path, strerror(errno));

		return ERR_PTR(err);

	}



	err = -LIBBPF_ERRNO__FORMAT;



	elf = elf_begin(fd, ELF_C_READ, NULL);

	if (!elf) {

		pr_warning("failed to open %s as ELF file\n", path);

		goto done;

	}

	if (!gelf_getehdr(elf, &ehdr)) {

		pr_warning("failed to get EHDR from %s\n", path);

		goto done;

	}

	if (!btf_check_endianness(&ehdr)) {

		pr_warning("non-native ELF endianness is not supported\n");

		goto done;

	}

	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {

		pr_warning("failed to get e_shstrndx from %s\n", path);

		goto done;

	}



	while ((scn = elf_nextscn(elf, scn)) != NULL) {

		GElf_Shdr sh;

		char *name;



		idx++;

		if (gelf_getshdr(scn, &sh) != &sh) {

			pr_warning("failed to get section(%d) header from %s\n",

				   idx, path);

			goto done;

		}

		name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);

		if (!name) {

			pr_warning("failed to get section(%d) name from %s\n",

				   idx, path);

			goto done;

		}

		if (strcmp(name, BTF_ELF_SEC) == 0) {

			btf_data = elf_getdata(scn, 0);

			if (!btf_data) {

				pr_warning("failed to get section(%d, %s) data from %s\n",

					   idx, name, path);

				goto done;

			}

			continue;

		} else if (btf_ext && strcmp(name, BTF_EXT_ELF_SEC) == 0) {

			btf_ext_data = elf_getdata(scn, 0);

			if (!btf_ext_data) {

				pr_warning("failed to get section(%d, %s) data from %s\n",

					   idx, name, path);

				goto done;

			}

			continue;

		}

	}



	err = 0;



	if (!btf_data) {

		err = -ENOENT;

		goto done;

	}

	btf = btf__new(btf_data->d_buf, btf_data->d_size);

	if (IS_ERR(btf))

		goto done;



	if (btf_ext && btf_ext_data) {

		*btf_ext = btf_ext__new(btf_ext_data->d_buf,

					btf_ext_data->d_size);

		if (IS_ERR(*btf_ext))

			goto done;

	} else if (btf_ext) {

		*btf_ext = NULL;

	}

done:

	if (elf)

		elf_end(elf);

	close(fd);



	if (err)

		return ERR_PTR(err);

	/*

	 * btf is always parsed before btf_ext, so no need to clean up

	 * btf_ext, if btf loading failed

	 */

	if (IS_ERR(btf))

		return btf;

	if (btf_ext && IS_ERR(*btf_ext)) {

		btf__free(btf);

		err = PTR_ERR(*btf_ext);

		return ERR_PTR(err);

	}

	return btf;

}



static int compare_vsi_off(const void *_a, const void *_b)

{

	const struct btf_var_secinfo *a = _a;

tools/lib/bpf/btf.h

+2 −0
Original line number Diff line number Diff line
@@ -59,6 +59,8 @@ struct btf_ext_header { 


LIBBPF_API void btf__free(struct btf *btf);

LIBBPF_API struct btf *btf__new(__u8 *data, __u32 size);

LIBBPF_API struct btf *btf__parse_elf(const char *path,

				      struct btf_ext **btf_ext);

LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);

LIBBPF_API int btf__load(struct btf *btf);

LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,

tools/lib/bpf/libbpf.map

+5 −0
Original line number Diff line number Diff line
@@ -164,3 +164,8 @@ LIBBPF_0.0.3 { 
		bpf_map_freeze;

		btf__finalize_data;

} LIBBPF_0.0.2;



LIBBPF_0.0.4 {

	global:

		btf__parse_elf;

} LIBBPF_0.0.3;

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