From: Peter Maydell Date: Thu, 12 Mar 2026 18:28:00 +0000 (+0000) Subject: hw/net/rtl8319: Work around GCC sanitizer / -Wstringop-overflow bug X-Git-Tag: v11.0.0-rc0~10^2~16 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b83a42dc779a36b454ce6eeade4584018491faf4;p=thirdparty%2Fqemu.git hw/net/rtl8319: Work around GCC sanitizer / -Wstringop-overflow bug If you compile QEMU with GCC with -fsanitize=address and -Wstringop-overflow, this causes GCC to produce a false-positive warning which it does not produce when the sanitizer is not enabled (and which makes compilation fail if you're using -Werror, as we do by default for builds from git): ../../hw/net/rtl8139.c: In function ‘rtl8139_io_writeb’: ../../hw/net/rtl8139.c:2264:17: error: writing 8 bytes into a region of size 0 [-Werror=stringop-overflow=] 2264 | memcpy(data_to_checksum, saved_ip_header + 12, 8); | ^ In file included from ../../hw/net/rtl8139.c:62: /home/pm215/qemu/include/net/eth.h:50:14: note: at offset [8, 48] into destination object ‘ip_ver_len’ of size 1 50 | uint8_t ip_ver_len; /* version and header length */ | ^~~~~~~~~~ ../../hw/net/rtl8139.c:2192:21: error: writing 8 bytes into a region of size 0 [-Werror=stringop-overflow=] 2192 | memcpy(data_to_checksum, saved_ip_header + 12, 8); | ^ /home/pm215/qemu/include/net/eth.h:50:14: note: at offset [8, 48] into destination object ‘ip_ver_len’ of size 1 50 | uint8_t ip_ver_len; /* version and header length */ | ^~~~~~~~~~ ../../hw/net/rtl8139.c:2192:21: error: writing 8 bytes into a region of size 0 [-Werror=stringop-overflow=] 2192 | memcpy(data_to_checksum, saved_ip_header + 12, 8); | ^ /home/pm215/qemu/include/net/eth.h:50:14: note: at offset [8, 48] into destination object ‘ip_ver_len’ of size 1 50 | uint8_t ip_ver_len; /* version and header length */ | ^~~~~~~~~~ In file included from /home/pm215/qemu/include/system/memory.h:21, from /home/pm215/qemu/include/hw/pci/pci.h:4, from /home/pm215/qemu/include/hw/pci/pci_device.h:4, from ../../hw/net/rtl8139.c:54: In function ‘stl_he_p’, inlined from ‘stl_be_p’ at /home/pm215/qemu/include/qemu/bswap.h:371:5, inlined from ‘rtl8139_cplus_transmit_one’ at ../../hw/net/rtl8139.c:2244:21, inlined from ‘rtl8139_cplus_transmit’ at ../../hw/net/rtl8139.c:2345:28, inlined from ‘rtl8139_io_writeb’ at ../../hw/net/rtl8139.c:2728:17: /home/pm215/qemu/include/qemu/bswap.h:284:5: error: writing 4 bytes into a region of size 0 [-Werror=stringop-overflow=] 284 | __builtin_memcpy(ptr, &v, sizeof(v)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /home/pm215/qemu/include/net/eth.h: In function ‘rtl8139_io_writeb’: /home/pm215/qemu/include/net/eth.h:50:14: note: at offset [24, 64] into destination object ‘ip_ver_len’ of size 1 50 | uint8_t ip_ver_len; /* version and header length */ | ^~~~~~~~~~ This has been triaged as a bug in GCC: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114494 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99673 (the sanitizer pass rewrites the IR in a way that conflicts with its use by the warning pass that runs afterwards). Since this is the only place in our code where we hit this, work around it by disabling the -Wstringop-overflow in the part of the function that hits it. We do this only when using the address sanitizer on GCC, so that we still get the benefit of the warning in most compilation scenarios. Cc: qemu-stable@nongnu.org Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3006 Suggested-by: Daniel P. Berrangé Signed-off-by: Peter Maydell Tested-by: Alex Bennée Tested-by: Yodel Eldar Reviewed-by: Alex Bennée Reviewed-by: Thomas Huth Message-id: 20260305140512.1330691-1-peter.maydell@linaro.org --- diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c index 2ad6338ebee..424af73a18f 100644 --- a/hw/net/rtl8139.c +++ b/hw/net/rtl8139.c @@ -2124,6 +2124,26 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) hlen, ip->ip_sum); } + /* + * The code in this function triggers a GCC bug where an + * interaction between -fsanitize=address and -Wstringop-overflow + * results in a false-positive stringop-overflow warning that is + * only emitted when the address sanitizer is enabled: + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114494 + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99673 + * GCC incorrectly thinks that the eth_payload_data buffer has + * the type and size of the first field in 'struct ip_header', i.e. + * one byte, and then complains about all other attempts to access + * data in the buffer. + * + * Work around this by disabling the warning when building with + * GCC and the address sanitizer is enabled. + */ +#pragma GCC diagnostic push +#if !defined(__clang__) && defined(QEMU_SANITIZE_ADDRESS) +#pragma GCC diagnostic ignored "-Wstringop-overflow" +#endif + if ((txdw0 & CP_TX_LGSEN) && ip_protocol == IP_PROTO_TCP) { /* Large enough for the TCP header? */ @@ -2307,6 +2327,9 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s) /* restore IP header */ memcpy(eth_payload_data, saved_ip_header, hlen); } + +#pragma GCC diagnostic pop + } skip_offload: