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

[Eric Gallager <egall@gwmail.gwu.edu>]

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...