From 5290b6f13e493b3fc814b4dc7fac2b5d7c252245 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Wed, 28 Sep 2022 20:45:55 +0200 Subject: [PATCH] udp: Replace pragma to ignore bogus stringop-overread warning with workaround Commit c318ffcb4c93 ("udp: Ignore bogus -Wstringop-overread for write() from gcc 12.1") uses a gcc pragma to ignore a bogus warning, which started appearing on gcc 12.1 (aarch64 and x86_64) due to: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103483 ...but gcc 12.2 has the same issue. Not just that: if LTO is enabled, the pragma itself is ignored (this wasn't the case with gcc 12.1), because of: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80922 Drop the pragma, and assign a frame (in the networking sense) pointer from the offset of the Ethernet header in the buffer, then pass it to write() and pcap(), so that gcc doesn't obsess anymore with the fact that an Ethernet header is 14 bytes and we're sending more than that. Signed-off-by: Stefano Brivio --- udp.c | 26 ++++++++++++++++++-------- util.h | 23 ----------------------- 2 files changed, 18 insertions(+), 31 deletions(-) diff --git a/udp.c b/udp.c index bd3dc72..d1be622 100644 --- a/udp.c +++ b/udp.c @@ -704,11 +704,20 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n, b->uh.len = htons(udp4_l2_mh_sock[n].msg_len + sizeof(b->uh)); if (c->mode == MODE_PASTA) { - PRAGMA_STRINGOP_OVERREAD_IGNORE - if (write(c->fd_tap, &b->eh, sizeof(b->eh) + ip_len) < 0) + /* If we pass &b->eh directly to write(), starting from + * gcc 12.1, at least on aarch64 and x86_64, we get a bogus + * stringop-overread warning, due to: + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103483 + * + * but we can't disable it with a pragma, because it will be + * ignored if LTO is enabled: + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80922 + */ + void *frame = (char *)b + offsetof(struct udp4_l2_buf_t, eh); + + if (write(c->fd_tap, frame, sizeof(b->eh) + ip_len) < 0) debug("tap write: %s", strerror(errno)); - PRAGMA_STRINGOP_OVERREAD_IGNORE_POP - pcap((char *)&b->eh, sizeof(b->eh) + ip_len); + pcap(frame, sizeof(b->eh) + ip_len); return; } @@ -805,11 +814,12 @@ static void udp_sock_fill_data_v6(const struct ctx *c, int n, b->ip6h.hop_limit = 255; if (c->mode == MODE_PASTA) { - PRAGMA_STRINGOP_OVERREAD_IGNORE - if (write(c->fd_tap, &b->eh, sizeof(b->eh) + ip_len) < 0) + /* See udp_sock_fill_data_v4() for the reason behind 'frame' */ + void *frame = (char *)b + offsetof(struct udp6_l2_buf_t, eh); + + if (write(c->fd_tap, frame, sizeof(b->eh) + ip_len) < 0) debug("tap write: %s", strerror(errno)); - PRAGMA_STRINGOP_OVERREAD_IGNORE_POP - pcap((char *)&b->eh, sizeof(b->eh) + ip_len); + pcap(frame, sizeof(b->eh) + ip_len); return; } diff --git a/util.h b/util.h index 0c3c994..0c06e34 100644 --- a/util.h +++ b/util.h @@ -96,29 +96,6 @@ void trace_init(int enable); (void *)(arg)); \ } while (0) - -#ifdef __has_warning -# if __has_warning("-Wstringop-overread") -# define PRAGMA_STRINGOP_OVERREAD_IGNORE \ - _Pragma("GCC diagnostic ignored \"-Wstringop-overread\"") -# define PRAGMA_STRINGOP_OVERREAD_IGNORE_POP \ - _Pragma("GCC diagnostic pop") -# else -# define PRAGMA_STRINGOP_OVERREAD_IGNORE -# define PRAGMA_STRINGOP_OVERREAD_IGNORE_POP -# endif -#else -# if defined(__GNUC__) && __GNUC__ >= 11 -# define PRAGMA_STRINGOP_OVERREAD_IGNORE \ - _Pragma("GCC diagnostic ignored \"-Wstringop-overread\"") -# define PRAGMA_STRINGOP_OVERREAD_IGNORE_POP \ - _Pragma("GCC diagnostic pop") -# else -# define PRAGMA_STRINGOP_OVERREAD_IGNORE -# define PRAGMA_STRINGOP_OVERREAD_IGNORE_POP -# endif -#endif - #if __BYTE_ORDER == __BIG_ENDIAN #define L2_BUF_ETH_IP4_INIT \ { \