| Message ID | 20231002144014.40c33922@hermes.local (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | [RFC] iproute2: ipila warning | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
Stephen Hemminger <stephen@networkplumber.org> writes: > Building current code with Debian stable Gcc 12.2.0 see this warning. > > CC ipila.o > ipila.c: In function ‘print_ila_locid’: > ipila.c:57:32: warning: ‘addr’ may be used uninitialized [-Wmaybe-uninitialized] > 57 | v = ntohs(words[i]); > | ^ > ipila.c:69:13: note: ‘addr’ declared here > 69 | static void print_ila_locid(const char *tag, int attr, struct rtattr *tb[]) > | ^~~~~~~~~~~~~~~ > > Looks like a Gcc aliasing bug. > Relevant snippets. > > static void print_addr64(__u64 addr, char *buff, size_t len) > { > __u16 *words = (__u16 *)&addr; > __u16 v; > int i, ret; > size_t written = 0; > char *sep = ":"; > > for (i = 0; i < 4; i++) { > v = ntohs(words[i]); > ... > > > static void print_ila_locid(const char *tag, int attr, struct rtattr *tb[]) > { > char abuf[256]; > > if (tb[attr]) > print_addr64(rta_getattr_u64(tb[attr]), > abuf, sizeof(abuf)); > > One solution would be to use a union. > Other would be to use some variation of no-strict aliasing. > > --- a/ip/ipila.c > +++ b/ip/ipila.c > @@ -47,14 +47,17 @@ static int genl_family = -1; > > static void print_addr64(__u64 addr, char *buff, size_t len) > { > - __u16 *words = (__u16 *)&addr; > + union { > + __u64 w64; > + __u16 words[4]; > + } id = { .w64 = addr }; This looks OK to me FWIW. Unions are commonly used to legalize aliasing, so anybody looking at this will understand what's going on. > __u16 v; > int i, ret; > size_t written = 0; > char *sep = ":"; > > for (i = 0; i < 4; i++) { > - v = ntohs(words[i]); > + v = ntohs(id.words[i]); > > if (i == 3) > sep = ""; > ..
--- a/ip/ipila.c +++ b/ip/ipila.c @@ -47,14 +47,17 @@ static int genl_family = -1; static void print_addr64(__u64 addr, char *buff, size_t len) { - __u16 *words = (__u16 *)&addr; + union { + __u64 w64; + __u16 words[4]; + } id = { .w64 = addr }; __u16 v; int i, ret; size_t written = 0; char *sep = ":"; for (i = 0; i < 4; i++) { - v = ntohs(words[i]); + v = ntohs(id.words[i]); if (i == 3) sep = "";
Building current code with Debian stable Gcc 12.2.0 see this warning. CC ipila.o ipila.c: In function ‘print_ila_locid’: ipila.c:57:32: warning: ‘addr’ may be used uninitialized [-Wmaybe-uninitialized] 57 | v = ntohs(words[i]); | ^ ipila.c:69:13: note: ‘addr’ declared here 69 | static void print_ila_locid(const char *tag, int attr, struct rtattr *tb[]) | ^~~~~~~~~~~~~~~ Looks like a Gcc aliasing bug. Relevant snippets. static void print_addr64(__u64 addr, char *buff, size_t len) { __u16 *words = (__u16 *)&addr; __u16 v; int i, ret; size_t written = 0; char *sep = ":"; for (i = 0; i < 4; i++) { v = ntohs(words[i]); ... static void print_ila_locid(const char *tag, int attr, struct rtattr *tb[]) { char abuf[256]; if (tb[attr]) print_addr64(rta_getattr_u64(tb[attr]), abuf, sizeof(abuf)); One solution would be to use a union. Other would be to use some variation of no-strict aliasing. ..