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

Yao Qi
2017-11-20T15:51:59Z

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)