https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85700
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-05-08
CC| |msebor at gcc dot gnu.org
Component|c++ |tree-optimization
Ever confirmed|0 |1
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed. Strncat is handled in maybe_diag_stxncpy_trunc() the same way as
strncpy and the approach doesn't seem right for the former. The following test
case shows the inconsistency. (The difference between C and C++ is due to the
C <string.h> defining strncat as a macro which suppresses the warning due to
-Wno-system-headers; in C++, strncat is defined as a function so
-Wno-system-headers has no effect on calls to it.)
$ cat u.c && gcc -O2 -S -Wall -ftrack-macro-expansion=0 /build/tmp/u.c
#define strncat __builtin_strncat
#define strlen __builtin_strlen
char a[4], b[4];
void f1 (void)
{
strncat (a, "1", sizeof a - strlen (a) - 1); // no warning (good)
}
void f2 (void)
{
strncat (a, "12", sizeof a - strlen (a) - 1); // bogus -Wstringop-truncation
}
void fx (void)
{
strncat (a, b, sizeof a - strlen (a) - 1); // bogus -Wstringop-truncation
}
/build/tmp/u.c: In function ‘f2’:
/build/tmp/u.c:13:3: warning: ‘__builtin_strncat’ output may be truncated
copying between 0 and 3 bytes from a string of length 2 [-Wstringop-truncation]
strncat (a, "12", sizeof a - strlen (a) - 1); // bogus
-Wstringop-truncation
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/build/tmp/u.c: In function ‘fx’:
/build/tmp/u.c:18:3: warning: ‘__builtin_strncat’ output may be truncated
copying between 0 and 3 bytes from a string of length 3 [-Wstringop-truncation]
strncat (a, b, sizeof a - strlen (a) - 1); // bogus
-Wstringop-truncation
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
