On Mon, 22 May 2023 09:34:53 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> This patch adds an instance method on `Linker`, namely
>> `Linker::canonicalLayouts` which returns all the layouts known by the linker
>> as implementing some ABI type. For instance, if I call this on my machine
>> (Linux/x64) I get this:
>>
>>
>> jshell> import java.lang.foreign.*;
>>
>> jshell> Linker.nativeLinker().canonicalLayouts()
>> $2 ==> {char16_t=c16, int8_t=b8, long=j64, size_t=j64, bool=z8, int=i32,
>> long long=j64, int64_t=j64, void*=a64, float=f32, char=b8, int16_t=s16,
>> int32_t=i32, short=s16, double=d64}
>>
>>
>> This can be useful to discover the ABI types supported by a linker
>> implementation, as well as for, in the future, add support for more exotic
>> (and platform-dependent) linker types, such as `long double` or `complex
>> long`.
>
> Maurizio Cimadamore has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Address further review comments
On further reflection i think mapping C `unsigned short` only to Java `char` is
a misleading. Although Java `char` is an integral type is not really intended
to be used generally as an unsigned 16-bit integer, so arguably Java `char` is
not as useful a carrier type for native interoperation as Java `short` might be
even though it is signed.
Thus i am inclined to remove that mapping.
What if we say something to the effect of:
> unless explicitly declared in the canonical layouts C's unsigned integral
> types are mapped to the layouts associated with the required C's signed
> integral types of the same bit sizes.
?
Arguably C `unsigned short` could map to carriers Java `short` or Java `char`,
but i am inclined to say the user should cast between Java `short` to `char` in
such cases.
FWIW i checked what the FFM API and jextract does today and it maps unsigned C
types to signed Java types.
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PR Comment: https://git.openjdk.org/jdk/pull/14037#issuecomment-1560028359
