Commit c86f180f authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Andrii Nakryiko
Browse files

libbpf: Make btf_parse_elf process .BTF.base transparently 



Update btf_parse_elf() to check if .BTF.base section is present.
The logic is as follows:

  if .BTF.base section exists:
     distilled_base := btf_new(.BTF.base)
  if distilled_base:
     btf := btf_new(.BTF, .base_btf=distilled_base)
     if base_btf:
        btf_relocate(btf, base_btf)
  else:
     btf := btf_new(.BTF)
  return btf

In other words:
- if .BTF.base section exists, load BTF from it and use it as a base
  for .BTF load;
- if base_btf is specified and .BTF.base section exist, relocate newly
  loaded .BTF against base_btf.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240613095014.357981-6-alan.maguire@oracle.com
parent affdeb50

tools/lib/bpf/btf.c

+110 −54
Original line number Diff line number Diff line
@@ -116,6 +116,9 @@ struct btf { 
	/* whether strings are already deduplicated */

	bool strs_deduped;



	/* whether base_btf should be freed in btf_free for this instance */

	bool owns_base;



	/* BTF object FD, if loaded into kernel */

	int fd;
@@ -969,6 +972,8 @@ void btf__free(struct btf *btf) 
	free(btf->raw_data);

	free(btf->raw_data_swapped);

	free(btf->type_offs);

	if (btf->owns_base)

		btf__free(btf->base_btf);

	free(btf);

}
@@ -1084,53 +1089,38 @@ struct btf *btf__new_split(const void *data, __u32 size, struct btf *base_btf) 
	return libbpf_ptr(btf_new(data, size, base_btf));

}



static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,

				 struct btf_ext **btf_ext)

struct btf_elf_secs {

	Elf_Data *btf_data;

	Elf_Data *btf_ext_data;

	Elf_Data *btf_base_data;

};



static int btf_find_elf_sections(Elf *elf, const char *path, struct btf_elf_secs *secs)

{

	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;

	Elf_Data *data;

	GElf_Ehdr ehdr;

	size_t shstrndx;

	int idx = 0;



	if (elf_version(EV_CURRENT) == EV_NONE) {

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

		return ERR_PTR(-LIBBPF_ERRNO__LIBELF);

	}



	fd = open(path, O_RDONLY | O_CLOEXEC);

	if (fd < 0) {

		err = -errno;

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

		goto done;

	}

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

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

		goto done;

		goto err;

	}



	if (elf_getshdrstrndx(elf, &shstrndx)) {

		pr_warn("failed to get section names section index for %s\n",

			path);

		goto done;

		goto err;

	}



	if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {

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

		goto done;

		goto err;

	}



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

		Elf_Data **field;

		GElf_Shdr sh;

		char *name;
@@ -1138,42 +1128,102 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, 
		if (gelf_getshdr(scn, &sh) != &sh) {

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

				idx, path);

			goto done;

			goto err;

		}

		name = elf_strptr(elf, shstrndx, sh.sh_name);

		if (!name) {

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

					idx, name, path);

				goto done;

			goto err;

		}



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

			field = &secs->btf_data;

		else if (strcmp(name, BTF_EXT_ELF_SEC) == 0)

			field = &secs->btf_ext_data;

		else if (strcmp(name, BTF_BASE_ELF_SEC) == 0)

			field = &secs->btf_base_data;

		else

			continue;

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

			btf_ext_data = elf_getdata(scn, 0);

			if (!btf_ext_data) {



		data = elf_getdata(scn, 0);

		if (!data) {

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

				idx, name, path);

				goto done;

			goto err;

		}

			continue;

		*field = data;

	}



	return 0;



err:

	return -LIBBPF_ERRNO__FORMAT;

}



	if (!btf_data) {

static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,

				 struct btf_ext **btf_ext)

{

	struct btf_elf_secs secs = {};

	struct btf *dist_base_btf = NULL;

	struct btf *btf = NULL;

	int err = 0, fd = -1;

	Elf *elf = NULL;



	if (elf_version(EV_CURRENT) == EV_NONE) {

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

		return ERR_PTR(-LIBBPF_ERRNO__LIBELF);

	}



	fd = open(path, O_RDONLY | O_CLOEXEC);

	if (fd < 0) {

		err = -errno;

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

		return ERR_PTR(err);

	}



	elf = elf_begin(fd, ELF_C_READ, NULL);

	if (!elf) {

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

		goto done;

	}



	err = btf_find_elf_sections(elf, path, &secs);

	if (err)

		goto done;



	if (!secs.btf_data) {

		pr_warn("failed to find '%s' ELF section in %s\n", BTF_ELF_SEC, path);

		err = -ENODATA;

		goto done;

	}

	btf = btf_new(btf_data->d_buf, btf_data->d_size, base_btf);

	err = libbpf_get_error(btf);



	if (secs.btf_base_data) {

		dist_base_btf = btf_new(secs.btf_base_data->d_buf, secs.btf_base_data->d_size,

					NULL);

		if (IS_ERR(dist_base_btf)) {

			err = PTR_ERR(dist_base_btf);

			dist_base_btf = NULL;

			goto done;

		}

	}



	btf = btf_new(secs.btf_data->d_buf, secs.btf_data->d_size,

		      dist_base_btf ?: base_btf);

	if (IS_ERR(btf)) {

		err = PTR_ERR(btf);

		goto done;

	}

	if (dist_base_btf && base_btf) {

		err = btf__relocate(btf, base_btf);

		if (err)

			goto done;

		btf__free(dist_base_btf);

		dist_base_btf = NULL;

	}



	if (dist_base_btf)

		btf->owns_base = true;



	switch (gelf_getclass(elf)) {

	case ELFCLASS32:
@@ -1187,11 +1237,12 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, 
		break;

	}



	if (btf_ext && btf_ext_data) {

		*btf_ext = btf_ext__new(btf_ext_data->d_buf, btf_ext_data->d_size);

		err = libbpf_get_error(*btf_ext);

		if (err)

	if (btf_ext && secs.btf_ext_data) {

		*btf_ext = btf_ext__new(secs.btf_ext_data->d_buf, secs.btf_ext_data->d_size);

		if (IS_ERR(*btf_ext)) {

			err = PTR_ERR(*btf_ext);

			goto done;

		}

	} else if (btf_ext) {

		*btf_ext = NULL;

	}
@@ -1205,6 +1256,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf, 


	if (btf_ext)

		btf_ext__free(*btf_ext);

	btf__free(dist_base_btf);

	btf__free(btf);



	return ERR_PTR(err);
@@ -5598,5 +5650,9 @@ void btf_set_base_btf(struct btf *btf, const struct btf *base_btf) 


int btf__relocate(struct btf *btf, const struct btf *base_btf)

{

	return libbpf_err(btf_relocate(btf, base_btf, NULL));

	int err = btf_relocate(btf, base_btf, NULL);



	if (!err)

		btf->owns_base = false;

	return libbpf_err(err);

}

tools/lib/bpf/btf.h

+1 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ extern "C" { 


#define BTF_ELF_SEC ".BTF"

#define BTF_EXT_ELF_SEC ".BTF.ext"

#define BTF_BASE_ELF_SEC ".BTF.base"

#define MAPS_ELF_SEC ".maps"



struct btf;