c-icap coredumps on Fedora 42

[frankcrawford]

c-icap coredumps on startup on Fedora 42, by the looks of it, due to issue with GCC 15 and debug printing. Dump from systemctl gives:

Jul 20 19:11:33 bits.crawford.emu.id.au systemd[1]: Started c-icap.service - c-icap is an implementation of an ICAP server.
Jul 20 19:11:33 bits.crawford.emu.id.au systemd-coredump[637329]: [🡕] Process 637327 (c-icap) of user 387 dumped core.
                                                                  
                                                                  Module /usr/bin/c-icap from rpm c-icap-0.6.3-2.fc42.x86_64
                                                                  Module srv_echo.so from rpm c-icap-0.6.3-2.fc42.x86_64
                                                                  Module libcrypto.so.3 from rpm openssl-3.2.4-4.fc42.x86_64
                                                                  Module libssl.so.3 from rpm openssl-3.2.4-4.fc42.x86_64
                                                                  Module libpcre2-8.so.0 from rpm pcre2-10.45-1.fc42.x86_64
                                                                  Module libbrotlienc.so.1 from rpm brotli-1.1.0-6.fc42.x86_64
                                                                  Module libbrotlidec.so.1 from rpm brotli-1.1.0-6.fc42.x86_64
                                                                  Module libbrotlicommon.so.1 from rpm brotli-1.1.0-6.fc42.x86_64
                                                                  Module libbz2.so.1 from rpm bzip2-1.0.8-20.fc42.x86_64
                                                                  Module libz.so.1 from rpm zlib-ng-2.2.4-3.fc42.x86_64
                                                                  Module libicapapi.so.6 from rpm c-icap-0.6.3-2.fc42.x86_64
                                                                  Stack trace of thread 637327:
                                                                  #0  0x0000556d00000000 n/a (n/a + 0x0)
                                                                  #1  0x0000556d6f7274b1 cfg_load_service (/usr/bin/c-icap + 0xd4b1)
                                                                  #2  0x0000556d6f727f01 parse_file (/usr/bin/c-icap + 0xdf01)
                                                                  #3  0x0000556d6f71d095 main (/usr/bin/c-icap + 0x3095)
                                                                  #4  0x00007ffb6c0bd5f5 __libc_start_call_main (libc.so.6 + 0x35f5)
                                                                  #5  0x00007ffb6c0bd6a8 __libc_start_main@@GLIBC_2.34 (libc.so.6 + 0x36a8)
                                                                  #6  0x0000556d6f71f2a5 _start (/usr/bin/c-icap + 0x52a5)
                                                                  ELF object binary architecture: AMD x86-64
Jul 20 19:11:33 bits.crawford.emu.id.au systemd[1]: c-icap.service: Main process exited, code=dumped, status=11/SEGV
Jul 20 19:11:33 bits.crawford.emu.id.au systemd[1]: c-icap.service: Failed with result 'core-dump'.

Far further debugging indicates that the issue come from calls to ci_debug_print, but not in all cases, see debug output:

Enabling parameter -D                                                           
Searching 0x555555586bd0 for default value
Setting parameter: PidFile=/run/c-icap/c-icap.pid
Searching 0x555555586bd8 for default value
Setting parameter: CommandsSocket=/run/c-icap/c-icap.ctl
Searching 0x55555558602c for default value
Setting parameter: Timeout=300
Searching 0x55555558600c for default value
Setting parameter: MaxKeepAliveRequests=100
Searching 0x555555586008 for default value
Setting parameter: KeepAliveTimeout=600
Searching 0x555555586c28 for default value
Setting parameter: StartServers=3
Searching 0x555555586c2c for default value
Setting parameter: MaxServers=10
Searching 0x555555586c34 for default value
Setting parameter: MinSpareThreads=10
Searching 0x555555586c38 for default value
Setting parameter: MaxSpareThreads=20
Searching 0x555555586c30 for default value
Setting parameter: ThreadsPerChild=10
Searching 0x555555587928 for default value
Setting parameter: MaxRequestsPerChild=0
Requested size 2048, getting buffer 0x555555595ae0 from pool 31:2048
Searching 0x555555586c18 for default value
Setting parameter: ServerAdmin=webmaster@crawford.emu.id.au
Searching 0x555555586c20 for default value
Setting parameter: ServerName=www.crawford.emu.id.au
Searching 0x555555586bc8 for default value
Setting parameter: TmpDir=/var/tmp
Searching 0x5555555871dc for default value

Program received signal SIGSEGV, Segmentation fault.
0x0000555500000000 in ?? ()

In addition, running as /usr/sbin/c-icap -N -f /etc/c-icap/c-icap.conf -d -1 which suppresses any debugging, allows it to startup.

I believe it is related to https://gcc.gnu.org/gcc-15/porting_to.html and in particular Function declarations without parameters although not exactly this issue.