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Re: Calling a machine code/binary function given its address, return type, & parameter types

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Richard Damon <Richard@Damon-Family.org> writes:
> On 8/17/19 6:10 PM, Keith Thompson wrote:
>> David Williams <dwilliams1664@gmail.com> writes:
> ...
>>> The platform is 64-bit Linux (x86-64).
>> 
>> Others have discussed how you can do this *if it can be done*.  But
>> there is no way to do this in portable C.  But since you're dealing with
>> calling machine code routines, you're probably not too concerned about
>> portability.
>
> Actually, since he knows the platform and that has been specified, he
> probably only really needs portable on that platform. I am pretty sure
> the ABI for that platform says that uintptr_t will exist and alias the
> same type as uint64_t which I think is unsigned long long (not as sure
> on that last point).

Sure -- but if the OP really needs to use an integer type to represent a
pointer value, using uintptr_t makes the code clearer.

I often find that portable code is clearer than non-portable code, even
if portability is not a concern.  (Often, not always.)

> I am also pretty sure that the platform ABI will define how casting that
> type to a function pointer will work (Linux has needs for that operation
> for things like share libraries, so they will define how it should work).
>
> Given that, assuming he is using a proper compiler for the environment,
> it should work.

Agreed.  See POSIX dlsym(), for example, which assumes you can can
convert a void* to a function pointer.  But if you need to convert void*
to a function pointer type, you should at least be aware that gcc will
complain about it *if* you use certain options.  (It also doesn't hurt
to be aware that, at the very least, the C standard doesn't define the
behavior.)

Some of these issues don't apply to converting an integer to a function
pointer.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */

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Calling a machine code/binary function given its address, return type, & parameter types David Williams <dwilliams1664@gmail.com> - 2019-08-17 06:58 -0700
  Re: Calling a machine code/binary function given its address, return type, & parameter types Richard Damon <Richard@Damon-Family.org> - 2019-08-17 10:14 -0400
  Re: Calling a machine code/binary function given its address, return type, & parameter types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-08-17 07:17 -0700
  Re: Calling a machine code/binary function given its address, return type, & parameter types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-17 15:26 +0100
  Re: Calling a machine code/binary function given its address, return type, & parameter types Siri Cruise <chine.bleu@yahoo.com> - 2019-08-17 12:15 -0700
  Re: Calling a machine code/binary function given its address, return type, & parameter types Bart <bc@freeuk.com> - 2019-08-17 20:34 +0100
    Re: Calling a machine code/binary function given its address, return type, & parameter types Keith Thompson <kst-u@mib.org> - 2019-08-17 14:31 -0700
  Re: Calling a machine code/binary function given its address, return type, & parameter types Keith Thompson <kst-u@mib.org> - 2019-08-17 15:10 -0700
    Re: Calling a machine code/binary function given its address, return type, & parameter types Richard Damon <Richard@Damon-Family.org> - 2019-08-17 20:09 -0400
      Re: Calling a machine code/binary function given its address, return type, & parameter types Keith Thompson <kst-u@mib.org> - 2019-08-17 17:54 -0700
  Re: Calling a machine code/binary function given its address, return type, & parameter types David Williams <dwilliams1664@gmail.com> - 2019-08-18 09:57 -0700
    Re: Calling a machine code/binary function given its address, return type, & parameter types Bart <bc@freeuk.com> - 2019-08-18 18:37 +0100
    Re: Calling a machine code/binary function given its address, return type, & parameter types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-18 21:40 +0100
    Re: Calling a machine code/binary function given its address, return type, & parameter types James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-21 09:05 -0400

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