Re: [PATCH v2 bpf-next 07/11] libbpf: add BPF static linker BTF and BTF.ext support

On Sat, Mar 13, 2021 at 11:35:33AM -0800, Andrii Nakryiko wrote:

+		for (j = 0; j < n; j++, src_var++) {
+			void *sec_vars = dst_sec->sec_vars;
+
+			sec_vars = libbpf_reallocarray(sec_vars,
+						       dst_sec->sec_var_cnt + 1,
+						       sizeof(*dst_sec->sec_vars));
+			if (!sec_vars)
+				return -ENOMEM;
+
+			dst_sec->sec_vars = sec_vars;
+			dst_sec->sec_var_cnt++;
+
+			dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
+			dst_var->type = obj->btf_type_map[src_var->type];
+			dst_var->size = src_var->size;
+			dst_var->offset = src_sec->dst_off + src_var->offset;
+		}
+	}
+
+	return 0;
+}
+
+static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
+{
+	size_t new_sz = (ext_data->rec_cnt + 1) * ext_data->rec_sz;
+	void *tmp;
+
+	tmp = realloc(ext_data->recs, new_sz);
+	if (!tmp)
+		return NULL;
+
+	ext_data->recs = tmp;
+	ext_data->rec_cnt++;
+
+	tmp += new_sz - ext_data->rec_sz;
+	memcpy(tmp, src_rec, ext_data->rec_sz);

while reading this and previous patch the cnt vs sz difference was
constantly throwing me off. Not a big deal, of course.
Did you consider using _cnt everywhere and use finalize method
to convert everything to size?
Like in this function libbpf_reallocarray() instead of realloc() would
probably be easier to read and more consistent, since btf_ext_sec_data
is measuring things in _cnt.
In the previous patch the section is in _sz which I guess is necessary
because sections can contain differently sized objects?

btw, strset abstraction is really nice. It made the patches much easier
to read.