On Sun, Jan 17, 2021 at 3:51 PM Florian Klämpfl via fpc-devel < fpc-devel@lists.freepascal.org> wrote:
> Am 08.01.21 um 22:00 schrieb Christo Crause via fpc-devel: > > On Sun, Oct 4, 2020 at 1:49 PM Christo Crause <christo.cra...@gmail.com > > <mailto:christo.cra...@gmail.com>> wrote: > > var > > w: word = $BEEF; section '.eeprom'; > > b: byte; > > > > procedure doSomething(constref tmp: word); > > begin > > b := hi(tmp); > > end; > > > > begin > > doSomething(w); > > end. > > > > At the moment there doesn't appear to be a way to do this without > > changing or adding something to the compiler. One idea could be to > > define new types identifying types in a specific address space, such as > > Teepromword. In this case the above example could be written as: > > var > > w: Teepromword = $BEEF; > > b: byte; > > > > procedure doSomething(constref tmp: word); overload; > > begin > > b := hi(tmp); > > end; > > > > procedure doSomething(constref tmp: Teepromword); overload; > > begin > > b := hi(tmp); > > end; > > > > begin > > doSomething(w); > > end. > > > > This way the compiler knows how to generate appropriate access based on > > the parameter type. It however leads to lots of code duplication. Which > > got me thinking about generics - could this be handled internally in the > > compiler via generics? It isn't clear to me how to tackle these issues > > so any advice would be appreciated. > > I would simply not allow to use such references as independent pointers. > This causes too much bloat. They can be used in assignments and > expressions and that's it. > I have given up on that idea. I'm now busy working on Jonas's suggestion of section specific pointers (example: https://github.com/ccrause/freepascal/wiki/Better-support-for-address-spaces-in-FPC#section-pointer-example ). At the moment it introduces no runtime overhead (other than the required access instructions of course), but to make it work across units is problematic. I suspect an extra field is required to store the section information associated with a pointer type (at least the way I've implemented it) in a ppu. If unit A defining such a pointer and a procedure using it is as parameter is called from unit B, it works if both units are compiled together. If unit A is already compiled and unit B is recompiled (symbols loaded from ppu) it doesn't carry the section information across and the compiler cannot determine which overloaded procedure to call.
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