initializing wider-than-pointers

[James E Wilson]

DJ Delorie wrote:
> For some chips, like xstormy16 and m16c, function pointers are wider
> than other pointers.

Trying to fake two kinds of pointers when we only have one doesn't seem 
wise to me.

A possible solution is to use function descriptors.  See FDESC_EXPR and 
ASM_OUTPUT_FDESC.  So now when you take the address of a function, you 
get a normal size pointer to a function descriptor.  The contents of a 
function descriptor are machine dependent, as determined by 
ASM_OUTPUT_FDESC, so you can easily put the entire address in there.

This has some advantages.  You don't need any machine independent gcc 
changes to make it work, and you don't need any (well, fewer) 
questionable C casts to get the full function address.

This also has disadvantages.  This is an ABI change.  You will need 
different code for calling through function pointers, though this may 
simplify or eliminate your thunks.  End users will have to know that 
function addresses are actually function descriptor addresses, and write 
and appropriate code.  If you want function comparisons to still work, 
you may need new relocs and linker support to handle function 
descriptors, to ensure that there is only one per function.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com