[dmd-internals] DMC vs DMD C++ mangling
Daniel Murphy
yebblies at gmail.com
Sat Apr 20 01:52:48 PDT 2013
On Sat, Apr 20, 2013 at 2:23 AM, Rainer Schuetze <r.sagitario at gmx.de> wrote:
> On 18.04.2013 15:22, Daniel Murphy wrote:
>
>> Hi all,
>>
>> I have come across one strange case where dmd and dmc produce different
>> mangling for seemingly identical declarations.
>>
>> D:
>> extern(C++) const(const(bool)*) gc_pi1; // mangled as ?gc_pi1@@3PB_NB
>>
>> C++:
>> extern bool const * const gc_pi1; // mangled as ?gc_pi1@@3QB_NB
>>
>> So we have '[PQ]B_NB' which translates to '[pointer/const pointer] const
>> bool const' where both of the const modifiers (for some reason) apply to
>> the bool, not the pointer.
>>
>
> If I understand Agner Fog (http://www.agner.org/**
> optimize/calling_conventions.**pdf<http://www.agner.org/optimize/calling_conventions.pdf>)
> correctly, "QB_NB" is parsed as QBtype with "QB" translating to "type
> *const" and type "_NB" translating to "const bool". So the const modifiers
> bind to different entities.
>
>
Further tests show the rightmost cv-modifier is not bound to the final
target type, but the first target type (target of the outmost indirection).
Agner's manual seems to imply that the rightmost cv-modifier is the
storage class of the declaration itself (although it doesn't explicitly say
this).
(All compiled with dmc)
extern bool const * const less_11; // ?less_11@@3 Q B _N B
extern bool const * less_10; // ?less_10@@3 P B _N B
extern bool * const less_01; // ?less_01@@3 Q A _N A
extern bool * less_00; // ?less_00@@3 P A _N A
extern bool const * const * const more_111; // ?more_111@@3 Q B Q B _N B
extern bool const * const * more_110; // ?more_110@@3 P B Q B _N B
extern bool const * * const more_101; // ?more_101@@3 Q A P B _N A
extern bool const * * more_100; // ?more_100@@3 P A P B _N A
extern bool * const * const more_011; // ?more_011@@3 Q B Q A _N B
extern bool * const * more_010; // ?more_010@@3 P B Q A _N B
extern bool * * const more_001; // ?more_001@@3 Q A P A _N A
extern bool * * more_000; // ?more_000@@3 P A P A _N A
extern bool const * const * const * const * const strange_11111; //
?strange_11111@@3 Q B Q B Q B Q B _N B
extern bool const * const * const * const * strange_11110; //
?strange_11110@@3 P B Q B Q B Q B _N B
extern bool const * const * const * * const strange_11101; //
?strange_11101@@3 Q A P B Q B Q B _N A
extern bool const * const * const * * strange_11100; //
?strange_11100@@3 P A P B Q B Q B _N A
extern bool const * const * * const * const strange_11011; //
?strange_11011@@3 Q B Q A P B Q B _N B
extern bool const * const * * const * strange_11010; //
?strange_11010@@3 P B Q A P B Q B _N B
extern bool const * const * * * const strange_11001; //
?strange_11001@@3 Q A P A P B Q B _N A
extern bool const * const * * * strange_11000; //
?strange_11000@@3 P A P A P B Q B _N A
extern bool const * * const * const * const strange_10111; //
?strange_10111@@3 Q B Q B Q A P B _N B
extern bool const * * const * const * strange_10110; //
?strange_10110@@3 P B Q B Q A P B _N B
extern bool const * * const * * const strange_10101; //
?strange_10101@@3 Q A P B Q A P B _N A
extern bool const * * const * * strange_10100; //
?strange_10100@@3 P A P B Q A P B _N A
extern bool const * * * const * const strange_10011; //
?strange_10011@@3 Q B Q A P A P B _N B
extern bool const * * * const * strange_10010; //
?strange_10010@@3 P B Q A P A P B _N B
extern bool const * * * * const strange_10001; //
?strange_10001@@3 Q A P A P A P B _N A
extern bool const * * * * strange_10000; //
?strange_10000@@3 P A P A P A P B _N A
extern bool * const * const * const * const strange_01111; //
?strange_01111@@3 Q B Q B Q B Q A _N B
extern bool * const * const * const * strange_01110; //
?strange_01110@@3 P B Q B Q B Q A _N B
extern bool * const * const * * const strange_01101; //
?strange_01101@@3 Q A P B Q B Q A _N A
extern bool * const * const * * strange_01100; //
?strange_01100@@3 P A P B Q B Q A _N A
extern bool * const * * const * const strange_01011; //
?strange_01011@@3 Q B Q A P B Q A _N B
extern bool * const * * const * strange_01010; //
?strange_01010@@3 P B Q A P B Q A _N B
extern bool * const * * * const strange_01001; //
?strange_01001@@3 Q A P A P B Q A _N A
extern bool * const * * * strange_01000; //
?strange_01000@@3 P A P A P B Q A _N A
extern bool * * const * const * const strange_00111; //
?strange_00111@@3 Q B Q B Q A P A _N B
extern bool * * const * const * strange_00110; //
?strange_00110@@3 P B Q B Q A P A _N B
extern bool * * const * * const strange_00101; //
?strange_00101@@3 Q A P B Q A P A _N A
extern bool * * const * * strange_00100; //
?strange_00100@@3 P A P B Q A P A _N A
extern bool * * * const * const strange_00011; //
?strange_00011@@3 Q B Q A P A P A _N B
extern bool * * * const * strange_00010; //
?strange_00010@@3 P B Q A P A P A _N B
extern bool * * * * const strange_00001; //
?strange_00001@@3 Q A P A P A P A _N A
extern bool * * * * strange_00000; //
?strange_00000@@3 P A P A P A P A _N A
> Is dmd incorrectly printing 'P' instead of 'Q' or have I missed something?
>>
>
> I suspect dmd might be omitting the transitive "const" to allow leaving
> "const char *" as is instead of requiring "const(char)*" when translating
> C++ headers to D.
>
>
Interesting. I'm not sure that's a good idea.
>
>
>> Thanks,
>> Daniel.
>>
>> PS If anybody with msvc installed could try this I would be very grateful.
>>
>
> cl 15.0 and 16.0 (from VS2008 and VS2010) mangle it the same as dmc:
>
> error LNK2019: unresolved external symbol "bool const * const gc_pi1"
> (?gc_pi1@@3QB_NB) referenced in function _main
>
Thanks, I'm going to classify dmd's behavior as a bug.
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