The following source, without the "(void*)" overrides, will throw an warning (as expected), when compiled with -Wall:
$ gcc -o memcpy-fortify -Wall memcpy-fortify.c memcpy-fortify.c: In function 'main': memcpy-fortify.c:21: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type memcpy-fortify.c:22: warning: passing argument 1 of 'strcpy' discards qualifiers from pointer target type With "(void*)" it is (as expected) silent. With -O2, it is silent, but with -D_FORTIFY_SOURCE != 0, the qualifier override is ignored: $ gcc -o memcpy-fortify -Wall -O2 -D_FORTIFY_SOURCE=2 memcpy-fortify.c memcpy-fortify.c: In function 'main': memcpy-fortify.c:21: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type memcpy-fortify.c:22: warning: passing argument 1 of 'strcpy' discards qualifiers from pointer target type This will cause problems for builds that run with -Werror. /* * gcc -o memcpy-fortify -Wall -Werror -O2 -D_FORTIFY_SOURCE=2 memcpy-fortify.c * */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <stdint.h> #include <string.h> #include <stdint.h> #include <inttypes.h> int main(int argc, char * argv[]) { char *foo = strdup("string one"); char *bar = strdup("string two"); const char *baz = (const char *)foo; printf("%s\n", foo); memcpy((void*)baz, bar, strlen(bar)+1); strcpy((void*)baz, bar); printf("%s\n", foo); return 0; } -- Summary: -D_FORTIFY_SOURCE discards qualifier overrides on {str,mem}cpy Product: gcc Version: 4.2.3 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: kees at outflux dot net http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35948