Difference between revisions of "FPC Internals/Parameters"

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The typical approach would be first to inspect variable specifier argument '''varspez'''.
 
The typical approach would be first to inspect variable specifier argument '''varspez'''.
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Normally, vs_var, vs_out, vs_constref are always passed by reference and '''push_addr_param''' should return true.
 
Normally, vs_var, vs_out, vs_constref are always passed by reference and '''push_addr_param''' should return true.
  

Revision as of 15:04, 15 October 2019

FPC is using the CPU target specified parameter manager to manage the location of parameters passed into and routines.


CPU target should implement parameter manager in cpupara.pas unit.

The unit should initialize the global ParaManager variable if an instance of the CPU specific class.

ParaManager:=tcpuparamanager.create

The basic TParaManager class cannot and should not be created, as it contain the abstract methods that should be implemented by CPU target implementation class.

Methods to Implement=

The following methods are critical for CPU target implementation

push_addr_param

Returns true if a parameter is too large to copy and only the address is pushed or if the parameter should be passed by reference.

 function push_addr_param(varspez:tvarspez;def : tdef;calloption : tproccalloption) : boolean;

The typical approach would be first to inspect variable specifier argument varspez.

Normally, vs_var, vs_out, vs_constref are always passed by reference and push_addr_param should return true.

In many cases var_const should return true as well, however, it's driven by CPU target ABI and calling convention. (for example, if definition (def) is a record and it can fit CPU word, then the value of the structure can be put into memory/register. Thus the function should return false)

create_paraloc_info

This is used to populate the location information on all parameters for the routine as seen in either the caller or the callee. It returns the size allocated on the stack

 function  create_paraloc_info(p : tabstractprocdef; side: tcallercallee):longint;

create_varargs_paraloc_info

This is used to populate the location information on all parameters for the routine that are passed as varargs. It returns the size allocated on the stack (including the normal parameters)

 function  create_varargs_paraloc_info(p : tabstractprocdef; side: tcallercallee; varargspara:tvarargsparalist):longint;

get_funcretloc

Returns the location of the function result if p had def as function result instead of its actual result. Used if the compiler forces the function result to something different than the real result.

 function  get_funcretloc(p : tabstractprocdef; side: tcallercallee; forcetempdef: tdef): tcgpara;

See Also