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Function pointers conversions and UB

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Hello,

Consider the following code:

void foo(struct s *arg) { }
void (*fp)(void *) = foo;

As far as I understand, this does /not/ have UB, because fp is not used
to call the function. Is that correct?

C99 6.3.2.3 p8
"A pointer to a function of one type may be converted to a pointer to a function of another
type and back again; the result shall compare equal to the original pointer. If a converted
pointer is used to call a function whose type is not compatible with the pointed-to type,
the behavior is undefined."

So the following code does have UB, correct?

void foo(struct s *arg) { }
void (*fp)(void *) = foo;
void bar(void) { fp(); } /* nasal demons from fp() */

I assume the behavior will be "it works as expected" on most platforms.
How/where will it blow up?

Platforms with different argument passing for void * and other pointers?

I lack imagination... What else? Pointer representation/encoding?

Regards.

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Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-11 21:26 +0100
  Re: Function pointers conversions and UB "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 15:57 -0500
    Re: Function pointers conversions and UB supercat@casperkitty.com - 2017-01-11 14:37 -0800
  Re: Function pointers conversions and UB jt@toerring.de (Jens Thoms Toerring) - 2017-01-11 21:46 +0000
  Re: Function pointers conversions and UB Keith Thompson <kst-u@mib.org> - 2017-01-11 13:51 -0800
    Re: Function pointers conversions and UB "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 17:06 -0500
  Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 00:29 +0100
    Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-11 23:37 +0000
      Re: Function pointers conversions and UB supercat@casperkitty.com - 2017-01-11 21:49 -0800
        Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 09:41 +0000
      Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 10:52 +0100
        Re: Function pointers conversions and UB Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 09:58 +0000
  Re: Function pointers conversions and UB Noob <root@127.0.0.1> - 2017-01-12 13:08 +0100
    Re: Function pointers conversions and UB Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-12 13:45 +0000

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