Den 14-02-2011 18:11, Jonas Maebe skrev:
On 14 Feb 2011, at 15:47, Jeppe Johansen wrote:
Okay, I understand what you mean. But then something more than "weak"
functionality should be added. Aliasing isn't the same, that's what
the "default" part does
procedure EmptyFunc; [public, alias: 'EmptyFunc'];
begin // Empty function
end;
procedure Func1; weak; external name 'Func1'; default 'EmptyFunc';
procedure Func2; weak; external name 'Func2'; default 'EmptyFunc';
The string after "name" always defines the name of what is referred to
by the external declaration, not to the name of whatever symbol you
are currently declaring. So the "default" actually means the same as
what "external" already means. We cannot change that specifically for
weak externals (regardless of the used syntax), as it would be
inconsistent with how regular external symbols are defined.
To add assembler names to a symbol definition, we use "alias" in FPC:
it means "define an alias with name 'name' for the current function".
I.e., you original example would become:
procedure NoHandler;
begin
// translated into:
// .globl NoHandler
// .NoHandler:
end;
procedure TestProcHandler; [public, alias: 'TestProc'];
begin
// translated into:
// .globl P$TestProcHandler
// P$TestProcHandler:
// .globl TestProc
// TestProc:
end;
... and then in some other unit, I guess (I'm not sure what the
interaction between the earlier regular "TestProc" defintion and the
weak "TestProc" declaration now would be otherwise):
procedure TestProc; weak; external name NoHandler'; alias: 'TestProc';
// translated into:
// a) on Linux
// .weak P$TestProc
// .set P$TestProc, NoHandler
// .weak TestProc
// .set TestProc, NoHandler
// b) on Mac OS X (and possibly on other non-ELF platforms):
// fail compilation, since weak symbol aliases don't exist and
there is no way to emulate this in the compiler
// (neither the specified name nor "alias" can be supported here
for weak externals)
...
begin
TestProc; // This will call TestProcHandler
end;
It has to be handled at the linker level, because the compiler has no
view of all code involved (there may be non-Pascal code too).
Jonas
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Okay. I get what you mean now
What about allowing a new keyword "weak" and let it have two
forms(something like you suggested back in one of the mails from 12th
january)? Name mangling is an issue of course. It would be easiest to
handle if weak symbols simply weren't name mangled(something like cdecl
and co)
procedure TestProc; weak; // This produces a weak symbol
begin
end;
procedure TestProc2; weak default 'SomeDefaultFunction'; // Weak+default
makes the declaration external by default
procedure TestProc3; weak default 'SomeDefaultFunction'; external name
'Test_TestProc3'; // Overcome eventual name mangling problems. Symbol is
called Test_TestProc3 and is linked to SomeDefaultFunction if not
resolved at linktime
procedure TestProc4; weak; external; // Replaces/does the same as
weakexternal
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