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tools/resolve_btfids: Emit warnings and patch zero id for missing sym…
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…bols

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
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Hengqi Chen authored and Andrii Nakryiko committed Jul 29, 2021
1 parent 33b57e0 commit 5aad036
Showing 1 changed file with 7 additions and 6 deletions.
13 changes: 7 additions & 6 deletions tools/bpf/resolve_btfids/main.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
Expand All @@ -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;
Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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++) {
Expand Down Expand Up @@ -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;
}

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