[Bug c/69704] New: goto *42 is not diagnosed

[Keith.S.Thompson at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69704

            Bug ID: 69704
           Summary: goto *42 is not diagnosed
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Keith.S.Thompson at gmail dot com
  Target Milestone: ---

This program:

int main(void) {
    goto *(void*)42;
}

shows a legal use of gcc's computed goto extension.

This program:

int main(void) {
    goto *42;
}

results in the same generated machine code, but is not consistent with the
documented extension, which permits the expression following "goto *" to be of
type void*. (An int value can be converted to void*, but only via an explicit
cast, or in the special case of a null pointer constant.)

The expression *42 by itself is correctly diagnosed as an error.

$ uname -a
Linux bomb20 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC
2015 x86_64 GNU/Linux
$ gcc --version
gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4

This was inspired by this question on Stack Overflow:

http://stackoverflow.com/q/35236834/827263

posted by user Sarvadi.