btf_encoder: Always initialize func_state to 0

BPF CI caught a segfault on aarch64 and s390x [1] after recent merges
into the master branch.

The segfault happened at free(func_state->annots) in
btf_encoder__delete_saved_funcs().

func_state->annots arrived there uninitialized because after patch [2]
in some cases func_state may be allocated with a realloc, but was not
zeroed out.

Fix this bug by always memset-ing a func_state to zero in
btf_encoder__alloc_func_state().

[1] https://github.com/kernel-patches/bpf/actions/runs/12700574327
[2] https://lore.kernel.org/dwarves/[email protected]/

Tested-by: Alan Maguire <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mykola Lysenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: theihor

btf_encoder.c

@@ -1083,7 +1083,7 @@ static bool funcs__match(struct btf_encoder_func_state *s1,
 
 static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_encoder *encoder)
 {
-	struct btf_encoder_func_state *tmp;
+	struct btf_encoder_func_state *state, *tmp;
 
 	if (encoder->func_states.cnt >= encoder->func_states.cap) {
 
@@ -1100,7 +1100,10 @@ static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_e
 		encoder->func_states.array = tmp;
 	}
 
-	return &encoder->func_states.array[encoder->func_states.cnt++];
+	state = &encoder->func_states.array[encoder->func_states.cnt++];
+	memset(state, 0, sizeof(*state));
+
+	return state;
 }
 
 static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct function *fn, struct elf_function *func)