libbpf: Ensure ELF symbols table is found before further ELF processing

libbpf ELF parsing logic might need symbols available before ELF parsing is
completed, so we need to make sure that symbols table section is found in
a separate pass before all the subsequent sections are processed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200903203542.15944-2-andriin@fb.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b688aadf09c5dea61c9349305ddeb23bc70152bf..ac56d4db6d3ed0bbf0cc6e0633c6545bd0b9b8fc 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2720,14 +2720,38 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
        Elf *elf = obj->efile.elf;
        Elf_Data *btf_ext_data = NULL;
        Elf_Data *btf_data = NULL;
-       Elf_Scn *scn = NULL;
        int idx = 0, err = 0;
+       const char *name;
+       Elf_Data *data;
+       Elf_Scn *scn;
+       GElf_Shdr sh;
 
+       /* a bunch of ELF parsing functionality depends on processing symbols,
+        * so do the first pass and find the symbol table
+        */
+       scn = NULL;
        while ((scn = elf_nextscn(elf, scn)) != NULL) {
-               const char *name;
-               GElf_Shdr sh;
-               Elf_Data *data;
+               if (elf_sec_hdr(obj, scn, &sh))
+                       return -LIBBPF_ERRNO__FORMAT;
+
+               if (sh.sh_type == SHT_SYMTAB) {
+                       if (obj->efile.symbols) {
+                               pr_warn("elf: multiple symbol tables in %s\n", obj->path);
+                               return -LIBBPF_ERRNO__FORMAT;
+                       }
 
+                       data = elf_sec_data(obj, scn);
+                       if (!data)
+                               return -LIBBPF_ERRNO__FORMAT;
+
+                       obj->efile.symbols = data;
+                       obj->efile.symbols_shndx = elf_ndxscn(scn);
+                       obj->efile.strtabidx = sh.sh_link;
+               }
+       }
+
+       scn = NULL;
+       while ((scn = elf_nextscn(elf, scn)) != NULL) {
                idx++;
 
                if (elf_sec_hdr(obj, scn, &sh))
@@ -2766,13 +2790,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                } else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
                        btf_ext_data = data;
                } else if (sh.sh_type == SHT_SYMTAB) {
-                       if (obj->efile.symbols) {
-                               pr_warn("elf: multiple symbol tables in %s\n", obj->path);
-                               return -LIBBPF_ERRNO__FORMAT;
-                       }
-                       obj->efile.symbols = data;
-                       obj->efile.symbols_shndx = idx;
-                       obj->efile.strtabidx = sh.sh_link;
+                       /* already processed during the first pass above */
                } else if (sh.sh_type == SHT_PROGBITS && data->d_size > 0) {
                        if (sh.sh_flags & SHF_EXECINSTR) {
                                if (strcmp(name, ".text") == 0)