Re: [PATCH][2.6.6-rc3] gcc-3.4.0 fixes

[Mikael Pettersson <mikpe@csd.uu.se>]

William Lee Irwin III writes:
 > On Tue, Jun 01, 2004 at 04:52:59PM +0200, Mikael Pettersson wrote:
 > > You're assuming pointers have uniform representation.
 > > C makes no such guarantees, and machines _have_ had
 > > different types of representations in the past.
 > > Some not-so-obsolete 64-bit machines in effect use fat
 > > representations for pointers to functions (descriptors),
 > > but they usually cheat and use pointers to the descriptors
 > > instead. However, a C implementation could legally
 > > represent a function pointer as a 128-bit value, while
 > > data pointers remain 64 bits.
 > 
 > IIRC for all types foo, sizeof(foo *) <= sizeof(void *), no?
 > If so, 128-bit function pointers implies >= 128-bit void pointers.

No, sizeof(foo*) <= sizeof(void*) only holds for data pointers.
The C standard is very explicit about not guaranteeing any
relationship between function pointers and void*. However,
a function pointer can be converted to a pointer to a different
function type and back again, without loss of information.

/Mikael