[Bug sanitizer/114494] New: false-positive with -O2 -Wstringop-overflow=2 -fsanitize=address

[akihiko.odaki at daynix dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114494

            Bug ID: 114494
           Summary: false-positive with -O2 -Wstringop-overflow=2
                    -fsanitize=address
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akihiko.odaki at daynix dot com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org
  Target Milestone: ---

Building
https://gitlab.com/qemu-project/qemu/-/commits/v9.0.0-rc1?ref_type=tags causes
the following warning:

cc -m64 -mcx16 -Ilibcommon.fa.p -Isubprojects/dtc/libfdt
-I../subprojects/dtc/libfdt -I/usr/include/glib-2.0
-I/usr/lib64/glib-2.0/include -I/usr/include/libmount -I/usr/include/blkid
-I/usr/include/sysprof-6 -I/usr/include/gio-unix-2.0 -fdiagnostics-color=auto
-Wall -Winvalid-pch -Werror -std=gnu11 -O2 -g -fsanitize=address
-fstack-protector-strong -Wempty-body -Wendif-labels -Wexpansion-to-defined
-Wformat-security -Wformat-y2k -Wignored-qualifiers -Wimplicit-fallthrough=2
-Winit-self -Wmissing-format-attribute -Wmissing-prototypes -Wnested-externs
-Wold-style-declaration -Wold-style-definition -Wredundant-decls -Wshadow=local
-Wstrict-prototypes -Wtype-limits -Wundef -Wvla -Wwrite-strings
-Wno-missing-include-dirs -Wno-psabi -Wno-shift-negative-value -isystem
/home/me/qemu/linux-headers -isystem linux-headers -iquote . -iquote
/home/me/qemu -iquote /home/me/qemu/include -iquote
/home/me/qemu/host/include/x86_64 -iquote /home/me/qemu/host/include/generic
-iquote /home/me/qemu/tcg/i386 -pthread -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64
-D_LARGEFILE_SOURCE -fno-strict-aliasing -fno-common -fwrapv
-ftrivial-auto-var-init=zero -fzero-call-used-regs=used-gpr -fPIE -MD -MQ
libcommon.fa.p/hw_net_rtl8139.c.o -MF libcommon.fa.p/hw_net_rtl8139.c.o.d -o
libcommon.fa.p/hw_net_rtl8139.c.o -c ../hw/net/rtl8139.c
../hw/net/rtl8139.c: In function 'rtl8139_io_writeb':
../hw/net/rtl8139.c:2273:17: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
 2273 |                 memcpy(data_to_checksum, saved_ip_header + 12, 8);

Below is a minimized reproduction case:
gcc -O2 -Wstringop-overflow=2 -fsanitize=address -c -x c - <<EOF
#include <string.h>

struct ip_header {
    char  ip_ver_len;
};

void rtl8139_cplus_transmit_one(char *saved_buffer)
{
    struct ip_header *ip;
    int hlen;

    char *eth_payload_data = saved_buffer + 4;

    ip = (struct ip_header*)eth_payload_data;

    hlen = ip->ip_ver_len;
    if (hlen < sizeof(struct ip_header)) {
        return;
    }

    char saved_ip_header[1];
    memcpy(saved_ip_header, eth_payload_data, hlen);
    memcpy(eth_payload_data + hlen, saved_ip_header, 1);
}
EOF