[PATCH] Wrap a macro in do {} while (0) (PR sanitizer/80063)

Martin Sebor msebor@gmail.com
Mon Mar 20 16:44:00 GMT 2017

On 03/20/2017 07:42 AM, Marek Polacek wrote:
> On Mon, Mar 20, 2017 at 09:37:10AM -0400, Jason Merrill wrote:
>> On Mon, Mar 20, 2017 at 9:28 AM, Marek Polacek <polacek@redhat.com> wrote:
>>> +  do {                                                                 \
>>> +    decl = add_builtin_function ("__builtin_" NAME, TYPE, ENUM,                \
>>> +                                BUILT_IN_NORMAL, NAME, NULL_TREE);     \
>>> +    set_call_expr_flags (decl, ATTRS);                                 \
>>> +    set_builtin_decl (ENUM, decl, true);                               \
>>> +  } while (0);
>> We leave out the trailing ; in a macro like this.
> True, but that wasn't possible in this case, otherwise I got tons of
> /home/marek/src/gcc/gcc/asan.c:2570:3: error: expected ‘;’ before ‘do’
>    do {         \
>    ^
> /home/marek/src/gcc/gcc/sanitizer.def:459:1: note: in expansion of macro ‘DEF_SANITIZER_BUILTIN’

I would view these as helpful errors and expect them to be fixed
by terminating the macro invocations with a semicolon rather than
by adding it to the macro definition itself.  Is there a problem
with doing that that I'm not considering?


PS The GCC manual documents this problem in the section titled
Swallowing the Semicolon:

This problem is also the subject of the CERT C Coding Standard
rule PRE11-C. Do not conclude macro definitions with a semicolon
(although the examples there are contrived).

Leaving the semicolon out also tends to confuse formatting tools.

It would be nice to be able to add a warning to help detect these
kinds of problems in macros (and others), and enable it for GCC

More information about the Gcc-patches mailing list