I have a question (for ROPS) in FPC that is way over my head.

- Can you find out how FPC expects string/interface/variant results ?

Is there documentation where I could get this information? I think it is about cpu registers, etc. (?)

Also, I might ask, how does FPC expect parameters passing? And Methods parameter passing?

Best regards.

This depends on the used calling convention. Especially on i386 there are many different ones. And from time to time this also changes to fix compatibility or performance issues. There is no definite documentation for this apart from the compiler source (which isn't easy to read, in particular if you are not even sure about concepts like cpu registers and how they can be used for parameter passing), or compiling test programs and looking at the generated assembler code (idem).

Jonas

Although the documentation of calling conventions isn't complete, it's probably worth to mention, that at least part of this information is available in our Programmer's Guide (section Calling Conventions/Calling mechanism). Additional information may be found in our mailing list archive
(http://community.freepascal.org:10000/lists/fpc-pascal/2004-May/006960.html).

Tomas

2006/11/1, Tomas Hajny :

I can read 'There are three calling conventions which have been used as the default in different versions of FPC'.

Will there be a final choice? Maybe my problem is that the calling convention has changed lately?

2006/11/1, Tomas Hajny :

Side question: Let say i would like to venture a little bit in asm programming, register stuff and how FPC use them... Any good doc available (asside FPC programmers guide) that I could use to lear quickly what I need to code my first full asm functions in pure asm?

Regards.

That's in other words what Jonas wrote too. Only two of them in stable versions/releases, though, and no changes within one major release number (i.e. one default convention for 1.x and another for 2.x).

Will there be a final choice? Maybe my problem is that the calling convention has changed lately?

Not that recently - the calling convention hasn't changed during 2.x lifetime. Moreover, you can still force the old behaviour, i.e. you aren't required to change your code necessarily. However, the newer convention is faster, which is the main reason for switching to it as new default. On top of that, there were some minor changes required for proper compatibility of the same calling convention with other compilers (bug fixes). We don't expect to change the current default any more (although we cannot guarantee that fully), and almost certainly not within 2.x series. However, it should be always possible for you to keep using the calling convention supported at one stage even in the future (regardless of potential future changes of a default one).

Tomas

Not that recently - the calling convention hasn't changed during 2.x lifetime. Moreover, you can still force the old behaviour, i.e. you aren't

Well, the calling conventions are changed if this is required because they are incompatible e.g. broken. So if we discover that we've e.g. wrong x86-64-linux calling conventions, we'll fix this of course.

Tomas Hajny wrote

We don't expect to change the current default any more (although we cannot guarantee that fully), and almost certainly not within 2.x series.

Actually, someone recently found out our register calling convention on i386 is incompatible with Delphi's for the parameters which don't fit in registers anymore. So that might still be changed, I guess.

Jonas