tools/resolve_btfids: Emit warnings and patch zero id for missing symbols

Kernel functions referenced by .BTF_ids may be changed from global to static
and get inlined or get renamed/removed, and thus disappears from BTF.
This causes kernel build failure when resolve_btfids do id patch for symbols
in .BTF_ids in vmlinux. Update resolve_btfids to emit warning messages and
patch zero id for missing symbols instead of aborting kernel build process.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210727132532.2473636-2-hengqi.chen@gmail.com

diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
index 3ad9301..de6365b 100644 (file)
--- a/tools/bpf/resolve_btfids/main.c
+++ b/tools/bpf/resolve_btfids/main.c
@@ -291,7 +291,7 @@ static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
        sh->sh_addralign = expected;
 
        if (gelf_update_shdr(scn, sh) == 0) {
-               printf("FAILED cannot update section header: %s\n",
+               pr_err("FAILED cannot update section header: %s\n",
                        elf_errmsg(-1));
                return -1;
        }
@@ -317,6 +317,7 @@ static int elf_collect(struct object *obj)
 
        elf = elf_begin(fd, ELF_C_RDWR_MMAP, NULL);
        if (!elf) {
+               close(fd);
                pr_err("FAILED cannot create ELF descriptor: %s\n",
                        elf_errmsg(-1));
                return -1;
@@ -484,7 +485,7 @@ static int symbols_resolve(struct object *obj)
        err = libbpf_get_error(btf);
        if (err) {
                pr_err("FAILED: load BTF from %s: %s\n",
-                       obj->path, strerror(-err));
+                       obj->btf ?: obj->path, strerror(-err));
                return -1;
        }
 
@@ -555,8 +556,7 @@ static int id_patch(struct object *obj, struct btf_id *id)
        int i;
 
        if (!id->id) {
-               pr_err("FAILED unresolved symbol %s\n", id->name);
-               return -EINVAL;
+               pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name);
        }
 
        for (i = 0; i < id->addr_cnt; i++) {
@@ -734,8 +734,9 @@ int main(int argc, const char **argv)
 
        err = 0;
 out:
-       if (obj.efile.elf)
+       if (obj.efile.elf) {
                elf_end(obj.efile.elf);
-       close(obj.efile.fd);
+               close(obj.efile.fd);
+       }
        return err;
 }