libbpf: Use string table index from index table if needed

For very large ELF objects (with many sections), we could
get special value SHN_XINDEX (65535) for elf object's string
table index - e_shstrndx.

Call elf_getshdrstrndx to get the proper string table index,
instead of reading it directly from ELF header.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210121202203.9346-4-jolsa@kernel.org

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 9970a288dda536768b5878f5f0a2c71dc0af8a97..d9c10830d749f0adefe37023c7210d55d5d28656 100644 (file)
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -858,6 +858,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
        Elf_Scn *scn = NULL;
        Elf *elf = NULL;
        GElf_Ehdr ehdr;
+       size_t shstrndx;
 
        if (elf_version(EV_CURRENT) == EV_NONE) {
                pr_warn("failed to init libelf for %s\n", path);
@@ -882,7 +883,14 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
                pr_warn("failed to get EHDR from %s\n", path);
                goto done;
        }
-       if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
+
+       if (elf_getshdrstrndx(elf, &shstrndx)) {
+               pr_warn("failed to get section names section index for %s\n",
+                       path);
+               goto done;
+       }
+
+       if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
                pr_warn("failed to get e_shstrndx from %s\n", path);
                goto done;
        }
@@ -897,7 +905,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
                                idx, path);
                        goto done;
                }
-               name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
+               name = elf_strptr(elf, shstrndx, sh.sh_name);
                if (!name) {
                        pr_warn("failed to get section(%d) name from %s\n",
                                idx, path);