gcc format-truncation warnings on Ubuntu 24.04

[rst0git]

Building CRIU on Ubuntu 24.04 (with gcc 13.2.0 and glibc 2.39) fails with the following errors:

  CC       criu/net.o
criu/net.c: In function ‘unix_conf_op’:
criu/net.c:236:32: error: ‘net/unix/’ directive output truncated writing 9 bytes into a region of size 0 [-Werror=format-truncation=]
  236 | #define CONF_UNIX_BASE         "net/unix"
      |                                ^~~~~~~~~~
criu/net.c:237:32: note: in expansion of macro ‘CONF_UNIX_BASE’
  237 | #define CONF_UNIX_FMT          CONF_UNIX_BASE "/%s"
      |                                ^~~~~~~~~~~~~~
criu/net.c:378:55: note: in expansion of macro ‘CONF_UNIX_FMT’
  378 |                 snprintf(path[i], MAX_CONF_UNIX_PATH, CONF_UNIX_FMT, unix_conf_entries[i]);
      |                                                       ^~~~~~~~~~~~~
criu/net.c:236:33: note: format string is defined here
  236 | #define CONF_UNIX_BASE         "net/unix"
      |                                 ^~~~~~~~~
  237 | #define CONF_UNIX_FMT          CONF_UNIX_BASE "/%s"
      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/stdio.h:980,
                 from /usr/include/libnl3/netlink/netlink.h:9,
                 from /usr/include/libnl3/netlink/attr.h:9,
                 from criu/net.c:16:
In function ‘snprintf’,
    inlined from ‘unix_conf_op’ at criu/net.c:378:3:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:54:10: note: ‘__builtin___snprintf_chk’ output 24 bytes into a destination of size 0
   54 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   55 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   56 |                                    __va_arg_pack ());
      |                                    ~~~~~~~~~~~~~~~~~
At top level:
cc1: note: unrecognized command-line option ‘-Wno-unknown-warning-option’ may have been intended to silence earlier diagnostics
cc1: all warnings being treated as errors

[adrianreber]

We tried it in the latest Fedora rawhide with GCC 14 and it does not happen there. I also do not see it on Fedora 40 (also GCC 14) and Fedora 39 which GCC 13.2. So not clear right now if that is Ubuntu specific or not.

[fweimer-rh]

@rst0git Could you provide full preprocessed sources (the .i file obtained from gcc -save-temps)? Then we can investigate further on the GCC side. Thanks.

[rst0git]

@fweimer-rh I have attached the content of net.i created with the following gcc command:
net.i.txt

$ gcc -save-temps -c -O2 -D_GNU_SOURCE -iquote include/ -I ./compel/include/uapi -fno-strict-aliasing -iquote criu/include -iquote include -iquote images -iquote criu/arch/x86/include -iquote . -I/usr/include/libnl3 criu/net.c -o criu/net.d 
criu/net.c: In function ‘unix_conf_op’:
criu/net.c:378:72: warning: ‘net/unix/’ directive output truncated writing 9 bytes into a region of size 0 [-Wformat-truncation=]
  378 |                 snprintf(path[i], MAX_CONF_UNIX_PATH, CONF_UNIX_FMT, unix_conf_entries[i]);
      |                                                                        ^~~~~~~~~~
In file included from /usr/include/stdio.h:980,
                 from /usr/include/libnl3/netlink/netlink.h:9,
                 from /usr/include/libnl3/netlink/attr.h:9,
                 from criu/net.c:16:
In function ‘snprintf’,
    inlined from ‘unix_conf_op’ at criu/net.c:378:3:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:54:10: note: ‘__builtin___snprintf_chk’ output 24 bytes into a destination of size 0
   54 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   55 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   56 |                                    __va_arg_pack ());
      |                                    ~~~~~~~~~~~~~~~~~~  

$ gcc --version
gcc (Ubuntu 13.2.0-23ubuntu4) 13.2.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ldd --version
ldd (Ubuntu GLIBC 2.39-0ubuntu8) 2.39
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.

[fweimer-rh]

Thanks, I can reproduce the warning with gcc-14.0.1-0.15.fc40.x86_64:

$ gcc -O2 -fno-strict-aliasing -c net.i  
In file included from /usr/include/stdio.h:980,
                 from /usr/include/libnl3/netlink/netlink.h:9,
                 from /usr/include/libnl3/netlink/attr.h:9,
                 from criu/net.c:16:
In function ‘snprintf’,
    inlined from ‘unix_conf_op’ at criu/net.c:378:3:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:54:10: warning: ‘__builtin___snprintf_chk’ specified bound 42 exceeds destination size 0 [-Wstringop-overflow=]

I'll try to look into this further, to see if it's a glibc header issue or more of a GCC thing.

[rst0git]

@fweimer-rh I'm not sure if it is the same warning:

$ gcc -O2 -fno-strict-aliasing -c net.i  
criu/net.c: In function ‘unix_conf_op’:
criu/net.c:378:58: warning: ‘net/unix/’ directive output truncated writing 9 bytes into a region of size 0 [-Wformat-truncation=]
In file included from /usr/include/stdio.h:980,
                 from /usr/include/libnl3/netlink/netlink.h:9,
                 from /usr/include/libnl3/netlink/attr.h:9,
                 from criu/net.c:16:
In function ‘snprintf’,
    inlined from ‘unix_conf_op’ at criu/net.c:378:3:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:54:10: note: ‘__builtin___snprintf_chk’ output 24 bytes into a destination of size 0
   54 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   55 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   56 |                                    __va_arg_pack ());
      |                                    ~~~~~~~~~~~~~~~~~~ 

[rst0git]

@fweimer-rh Note that the following change fixes the problem:

diff --git a/criu/net.c b/criu/net.c
index b5c4a6ee3..5486c4484 100644
--- a/criu/net.c
+++ b/criu/net.c
@@ -362,7 +362,7 @@ static int ipv6_conf_op(char *tgt, SysctlEntry **conf, int n, int op, SysctlEntr
 static int unix_conf_op(SysctlEntry ***rconf, size_t *n, int op)
 {
        int i, ret = -1, flags = 0;
-       char path[ARRAY_SIZE(unix_conf_entries)][MAX_CONF_UNIX_PATH] = {};
+       char path[ARRAY_SIZE(unix_conf_entries)+1][MAX_CONF_UNIX_PATH] = {};
        struct sysctl_req req[ARRAY_SIZE(unix_conf_entries)] = {};
        SysctlEntry **conf = *rconf;

I have attached the content of net.i with this change: net.i.txt