[PATCH v3 bpf-next 01/14] libbpf: ensure ELF symbols table is found before further ELF processing

[Andrii Nakryiko]

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.

Acked-by: John Fastabend <john.fastab...@gmail.com>
Signed-off-by: Andrii Nakryiko <andr...@fb.com>
---
 tools/lib/bpf/libbpf.c | 40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b688aadf09c5..ac56d4db6d3e 100644
--- 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)
-- 
2.24.1