[fpc-devel] Internal symbols

Jonas Maebe jonas at freepascal.org
Sun Feb 3 12:17:06 CET 2019

On 03/02/19 05:08, J. Gareth Moreton wrote:

> Basically, if you declare a public symbol (either using the "public" 
> directive or putting it in the interface section of a unit) with a name 
> that's identical to an internal symbol (I used "FPC_ABSMASK_DOUBLE"), 
> you get a 'duplicate symbol' linker error... in fact, Lazarus doesn't 
> even display the error (see bug #34996) - it only appears if you run the 
> compiler from the command line.

The FPC (and _FPC) namespace is reserved for internal use. Detecting 
such clashes is not possible without adding all declared external 
symbols to hash tables, which would reduce both compilation speed and 
increase memory usage. I think it's better to simply document that such 
symbols are reserved for compiler and RTL usage.

> You can get around the above issue if you simply rename the constant or 
> keep it private.  However, there is one other issue that is not so easy 
> to circumvent, and that's when you try to call an internal function 
> through assembly language (in this instance, I'm assuming the code is 
> not cross-platform and I'll be calling the x86_64 version of 
> fpc_int_real, which is "nostackframe" and only modifies XMM0 and RAX):

Calling internal functions directly is unsupported, which is the reason 
why they are made inaccessible from regular code. Their signature or 
behaviour can change across compiler versions (or they may even 
disappear altogether). You can hack around it by declaring external 
functions mapping to the symbol name of the internal function, but 
again, that is completely unsupported.


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