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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: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240613095014.357981-6-alan.maguire@oracle.com
This commit is contained in:
Eduard Zingerman
Andrii Nakryiko
parent
affdeb5061
commit
c86f180ffc
2 changed files with 122 additions and 65 deletions
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@ -116,6 +116,9 @@ struct btf {
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/* whether strings are already deduplicated */
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bool strs_deduped;
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/* whether base_btf should be freed in btf_free for this instance */
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bool owns_base;
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/* BTF object FD, if loaded into kernel */
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int fd;
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@ -969,6 +972,8 @@ void btf__free(struct btf *btf)
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free(btf->raw_data);
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free(btf->raw_data_swapped);
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free(btf->type_offs);
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if (btf->owns_base)
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btf__free(btf->base_btf);
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free(btf);
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}
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@ -1084,16 +1089,86 @@ struct btf *btf__new_split(const void *data, __u32 size, struct btf *base_btf)
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return libbpf_ptr(btf_new(data, size, base_btf));
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}
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struct btf_elf_secs {
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Elf_Data *btf_data;
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Elf_Data *btf_ext_data;
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Elf_Data *btf_base_data;
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};
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static int btf_find_elf_sections(Elf *elf, const char *path, struct btf_elf_secs *secs)
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{
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Elf_Scn *scn = NULL;
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Elf_Data *data;
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GElf_Ehdr ehdr;
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size_t shstrndx;
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int idx = 0;
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("failed to get EHDR from %s\n", path);
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goto err;
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}
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if (elf_getshdrstrndx(elf, &shstrndx)) {
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pr_warn("failed to get section names section index for %s\n",
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path);
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goto err;
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}
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if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
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pr_warn("failed to get e_shstrndx from %s\n", path);
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goto err;
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}
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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Elf_Data **field;
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GElf_Shdr sh;
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char *name;
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idx++;
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if (gelf_getshdr(scn, &sh) != &sh) {
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pr_warn("failed to get section(%d) header from %s\n",
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idx, path);
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goto err;
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}
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name = elf_strptr(elf, shstrndx, sh.sh_name);
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if (!name) {
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pr_warn("failed to get section(%d) name from %s\n",
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idx, path);
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goto err;
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}
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if (strcmp(name, BTF_ELF_SEC) == 0)
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field = &secs->btf_data;
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else if (strcmp(name, BTF_EXT_ELF_SEC) == 0)
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field = &secs->btf_ext_data;
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else if (strcmp(name, BTF_BASE_ELF_SEC) == 0)
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field = &secs->btf_base_data;
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else
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continue;
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data = elf_getdata(scn, 0);
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if (!data) {
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pr_warn("failed to get section(%d, %s) data from %s\n",
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idx, name, path);
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goto err;
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}
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*field = data;
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}
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return 0;
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err:
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return -LIBBPF_ERRNO__FORMAT;
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}
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static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
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struct btf_ext **btf_ext)
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{
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Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
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int err = 0, fd = -1, idx = 0;
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struct btf_elf_secs secs = {};
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struct btf *dist_base_btf = NULL;
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struct btf *btf = NULL;
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Elf_Scn *scn = NULL;
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int err = 0, fd = -1;
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Elf *elf = NULL;
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GElf_Ehdr ehdr;
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size_t shstrndx;
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if (elf_version(EV_CURRENT) == EV_NONE) {
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pr_warn("failed to init libelf for %s\n", path);
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@ -1107,73 +1182,48 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
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return ERR_PTR(err);
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}
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err = -LIBBPF_ERRNO__FORMAT;
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elf = elf_begin(fd, ELF_C_READ, NULL);
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if (!elf) {
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pr_warn("failed to open %s as ELF file\n", path);
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goto done;
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}
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("failed to get EHDR from %s\n", path);
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err = btf_find_elf_sections(elf, path, &secs);
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if (err)
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goto done;
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}
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if (elf_getshdrstrndx(elf, &shstrndx)) {
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pr_warn("failed to get section names section index for %s\n",
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path);
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goto done;
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}
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if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
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pr_warn("failed to get e_shstrndx from %s\n", path);
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goto done;
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}
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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GElf_Shdr sh;
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char *name;
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idx++;
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if (gelf_getshdr(scn, &sh) != &sh) {
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pr_warn("failed to get section(%d) header from %s\n",
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idx, path);
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goto done;
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}
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name = elf_strptr(elf, shstrndx, sh.sh_name);
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if (!name) {
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pr_warn("failed to get section(%d) name from %s\n",
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idx, path);
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goto done;
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}
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if (strcmp(name, BTF_ELF_SEC) == 0) {
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btf_data = elf_getdata(scn, 0);
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if (!btf_data) {
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pr_warn("failed to get section(%d, %s) data from %s\n",
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idx, name, path);
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goto done;
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}
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continue;
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} else if (btf_ext && strcmp(name, BTF_EXT_ELF_SEC) == 0) {
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btf_ext_data = elf_getdata(scn, 0);
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if (!btf_ext_data) {
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pr_warn("failed to get section(%d, %s) data from %s\n",
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idx, name, path);
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goto done;
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}
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continue;
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}
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}
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if (!btf_data) {
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if (!secs.btf_data) {
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pr_warn("failed to find '%s' ELF section in %s\n", BTF_ELF_SEC, path);
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err = -ENODATA;
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goto done;
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}
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btf = btf_new(btf_data->d_buf, btf_data->d_size, base_btf);
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err = libbpf_get_error(btf);
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if (err)
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if (secs.btf_base_data) {
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dist_base_btf = btf_new(secs.btf_base_data->d_buf, secs.btf_base_data->d_size,
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NULL);
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if (IS_ERR(dist_base_btf)) {
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err = PTR_ERR(dist_base_btf);
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dist_base_btf = NULL;
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goto done;
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}
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}
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btf = btf_new(secs.btf_data->d_buf, secs.btf_data->d_size,
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dist_base_btf ?: base_btf);
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if (IS_ERR(btf)) {
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err = PTR_ERR(btf);
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goto done;
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}
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if (dist_base_btf && base_btf) {
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err = btf__relocate(btf, base_btf);
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if (err)
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goto done;
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btf__free(dist_base_btf);
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dist_base_btf = NULL;
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}
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if (dist_base_btf)
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btf->owns_base = true;
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switch (gelf_getclass(elf)) {
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case ELFCLASS32:
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@ -1187,11 +1237,12 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
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break;
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}
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if (btf_ext && btf_ext_data) {
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*btf_ext = btf_ext__new(btf_ext_data->d_buf, btf_ext_data->d_size);
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err = libbpf_get_error(*btf_ext);
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if (err)
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if (btf_ext && secs.btf_ext_data) {
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*btf_ext = btf_ext__new(secs.btf_ext_data->d_buf, secs.btf_ext_data->d_size);
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if (IS_ERR(*btf_ext)) {
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err = PTR_ERR(*btf_ext);
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goto done;
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}
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} else if (btf_ext) {
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*btf_ext = NULL;
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}
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@ -1205,6 +1256,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
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if (btf_ext)
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btf_ext__free(*btf_ext);
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btf__free(dist_base_btf);
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btf__free(btf);
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return ERR_PTR(err);
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@ -5598,5 +5650,9 @@ void btf_set_base_btf(struct btf *btf, const struct btf *base_btf)
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int btf__relocate(struct btf *btf, const struct btf *base_btf)
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{
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return libbpf_err(btf_relocate(btf, base_btf, NULL));
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int err = btf_relocate(btf, base_btf, NULL);
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if (!err)
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btf->owns_base = false;
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return libbpf_err(err);
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}
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@ -18,6 +18,7 @@ extern "C" {
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#define BTF_ELF_SEC ".BTF"
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#define BTF_EXT_ELF_SEC ".BTF.ext"
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#define BTF_BASE_ELF_SEC ".BTF.base"
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#define MAPS_ELF_SEC ".maps"
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struct btf;
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