[PATCH bpf-next 3/3] libbpf: Use string table index from index table if needed

[Jiri Olsa]

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.

In such case we need to call elf_getshdrstrndx to get the
proper string table index.

Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 tools/lib/bpf/btf.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 3c3f2bc6c652..4fe987846bc0 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -863,6 +863,7 @@ 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);
@@ -887,7 +888,16 @@ 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)) {
+
+       /*
+        * Get string table index from extended section index
+        * table if needed.
+        */
+       shstrndx = ehdr.e_shstrndx;
+       if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx))
+               goto done;
+
+       if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
                pr_warn("failed to get e_shstrndx from %s\n", path);
                goto done;
        }
@@ -902,7 +912,7 @@ 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);
-- 
2.27.0