libbpf: Switch to void * casting in netlink helpers

Netlink helpers I added in 8bbb77b7 ("libbpf: Add various netlink
helpers") used char * casts everywhere, and there were a few more that
existed from before.

Convert all of them to void * cast, as it is treated equivalently by
clang/gcc for the purposes of pointer arithmetic and to follow the
convention elsewhere in the kernel/libbpf.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210619041454.417577-2-memxor@gmail.com

tools/lib/bpf/netlink.c

@@ -524,7 +524,7 @@ static int get_tc_info(struct nlmsghdr *nh, libbpf_dump_nlmsg_t fn,
 	struct nlattr *tb[TCA_MAX + 1];
 
 	libbpf_nla_parse(tb, TCA_MAX,
-			 (struct nlattr *)((char *)tc + NLMSG_ALIGN(sizeof(*tc))),
+			 (struct nlattr *)((void *)tc + NLMSG_ALIGN(sizeof(*tc))),
 			 NLMSG_PAYLOAD(nh, sizeof(*tc)), NULL);
 	if (!tb[TCA_KIND])
 		return NL_CONT;

tools/lib/bpf/nlattr.c

@@ -27,7 +27,7 @@ static struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
 	int totlen = NLA_ALIGN(nla->nla_len);
 
 	*remaining -= totlen;
-	return (struct nlattr *) ((char *) nla + totlen);
+	return (struct nlattr *)((void *)nla + totlen);
 }
 
 static int nla_ok(const struct nlattr *nla, int remaining)

tools/lib/bpf/nlattr.h

@@ -81,7 +81,7 @@ struct libbpf_nla_req {
  */
 static inline void *libbpf_nla_data(const struct nlattr *nla)
 {
-	return (char *) nla + NLA_HDRLEN;
+	return (void *)nla + NLA_HDRLEN;
 }
 
 static inline uint8_t libbpf_nla_getattr_u8(const struct nlattr *nla)
@@ -118,12 +118,12 @@ int libbpf_nla_dump_errormsg(struct nlmsghdr *nlh);
 
 static inline struct nlattr *nla_data(struct nlattr *nla)
 {
-	return (struct nlattr *)((char *)nla + NLA_HDRLEN);
+	return (struct nlattr *)((void *)nla + NLA_HDRLEN);
 }
 
 static inline struct nlattr *req_tail(struct libbpf_nla_req *req)
 {
-	return (struct nlattr *)((char *)req + NLMSG_ALIGN(req->nh.nlmsg_len));
+	return (struct nlattr *)((void *)req + NLMSG_ALIGN(req->nh.nlmsg_len));
 }
 
 static inline int nlattr_add(struct libbpf_nla_req *req, int type,
@@ -158,7 +158,7 @@ static inline struct nlattr *nlattr_begin_nested(struct libbpf_nla_req *req, int
 static inline void nlattr_end_nested(struct libbpf_nla_req *req,
 				     struct nlattr *tail)
 {
-	tail->nla_len = (char *)req_tail(req) - (char *)tail;
+	tail->nla_len = (void *)req_tail(req) - (void *)tail;
 }
 
 #endif /* __LIBBPF_NLATTR_H */