https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66516
Bug ID: 66516
Summary: missing diagnostic on taking the address of a builtin
function
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
Gcc accepts without warning code that takes the address of builtin functions
and calls such functions through pointers. Some such code links and even runs
successfully while other such code fails to link.
For example, code that compiles, links and runs:
$ cat z.c && gcc -Wall z.c && ./a.out
extern int printf (const char*, ...);
unsigned long strlen (const char*);
int main (void)
{
unsigned long (*p)(const char*) = &__builtin_strlen;
printf ("&__builtin_strlen = %p\n"
"&strlen = %p\n",
p, &strlen);
}
&__builtin_strlen = 0x400430
&strlen = 0x400430
Code that compiles but doesn't link involves builtins that don't have
corresponding libc functions.
Clang rejects all such code with an error similar to the following:
z.c:6:40: error: builtin functions must be directly called
unsigned long (*p)(const char*) = &__builtin_strlen;
^
1 error generated.
It seems that gcc should reject all code that attempts to take the address of a
builtin the same way Clang does.
