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libbpf: Fix segfault in static linker for objects without BTF

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When a BPF object is compiled without BTF info (without -g),
trying to link such objects using bpftool causes a SIGSEGV due to
btf__get_nr_types accessing obj->btf which is NULL. Fix this by
checking for the NULL pointer, and return error.

Reproducer:
$ cat a.bpf.c
extern int foo(void);
int bar(void) { return foo(); }
$ cat b.bpf.c
int foo(void) { return 0; }
$ clang -O2 -target bpf -c a.bpf.c
$ clang -O2 -target bpf -c b.bpf.c
$ bpftool gen obj out a.bpf.o b.bpf.o
Segmentation fault (core dumped)

After fix:
$ bpftool gen obj out a.bpf.o b.bpf.o
libbpf: failed to find BTF info for object 'a.bpf.o'
Error: failed to link 'a.bpf.o': Unknown error -22 (-22)

Fixes: a46349227cd8 (libbpf: Add linker extern resolution support for functions and global variables)
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210924023725.70228-1-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi 2021-09-24 08:07:25 +05:30 committed by Daniel Borkmann
parent b3aa173d58
commit bcfd367c28
1 changed files with 7 additions and 1 deletions
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8
tools/lib/bpf/linker.c
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@ -1649,11 +1649,17 @@ static bool btf_is_non_static(const struct btf_type *t)
static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
int *out_btf_sec_id, int *out_btf_id)
{
int i, j, n = btf__get_nr_types(obj->btf), m, btf_id = 0;
int i, j, n, m, btf_id = 0;
const struct btf_type *t;
const struct btf_var_secinfo *vi;
const char *name;
if (!obj->btf) {
pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
return -EINVAL;
}
n = btf__get_nr_types(obj->btf);
for (i = 1; i <= n; i++) {
t = btf__type_by_id(obj->btf, i);