Re: Fail to compile GDB with recent GCC trunk (-Werror=stringop-overflow=, -Werror=stringop-truncation)

Eric Gallager
2017-11-20T16:25:56Z

On 11/20/17, Yao Qi <qiyaoltc@gmail.com> wrote:
>
> Hi,
> I failed to compile GDB with GCC trunk (8.0.0 20171117) because of some
> -Werror=stringop-overflow= and -Werror=stringop-truncation warnings.
> Some of them are not necessary to me,
>
> 1. ../../binutils-gdb/gdb/python/py-gdb-readline.c:79:15: error: ‘char*
> strncpy(char*, const char*, size_t)’ output truncated before terminating nul
> copying as many bytes from a string as its length
> [-Werror=stringop-truncation]
> strncpy (q, p, n);
> ~~~~~~~~^~~~~~~~~
> ../../binutils-gdb/gdb/python/py-gdb-readline.c:73:14: note: length computed
> here
> n = strlen (p);
> ~~~~~~~^~~
>
> the code is simple,
>
> n = strlen (p);
>
> /* Copy the line to Python and return. */
> q = (char *) PyMem_RawMalloc (n + 2);
> if (q != NULL)
> {
> strncpy (q, p, n);
> q[n] = '\n';
> q[n + 1] = '\0';
> }
>
> I don't see the point of warning here.
>
> 2. ../../binutils-gdb/gdb/cp-namespace.c:1071:11: error: ‘char*
> strncpy(char*, const char*, size_t)’ output truncated before terminating nul
> copying 2 bytes from a string of the same length
> [-Werror=stringop-truncation]
> strncpy (full_name + scope_length, "::", 2);
> ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> full_name = (char *) alloca (scope_length + 2 + strlen (name) + 1);
> strncpy (full_name, scope, scope_length);
> strncpy (full_name + scope_length, "::", 2);
> strcpy (full_name + scope_length + 2, name);
>
> the code looks right to me,
>
> Likewise,
>
> ../../../binutils-gdb/gdb/gdbserver/remote-utils.c:1204:14: error: ‘char*
> strncpy(char*, const char*, size_t)’ output truncated before terminating nul
> copying 6 bytes from a string of the same length
> [-Werror=stringop-truncation]
> strncpy (buf, "watch:", 6);
> ~~~~~~~~^~~~~~~~~~~~~~~~~~
>
> strncpy (buf, "watch:", 6);
> buf += 6;
> ....
> *buf = '\0';
>
> I can "fix" these warnings by changing GDB code, use strcpy in 1) and
> use memcpy in 2). Do we expect all the users of GCC 8 changing their
> correct code because GCC is not happy on the code? The warning is too
> aggressive to me.
>
> --
> Yao (齐尧)
>

I thought there was a gcc bug open about this but now I can't seem to
find it; please let me know if you come across the one I was trying to
remember...