On Wed, 17 May 2023 18:18:03 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:
>
> Tweak javadoc
I wonder if we need to be stronger on the compatibility requirements for the
supported canonical layouts. It seems we can make stronger claims than symbols
made available by the default linker because the ABI supported by the linker
will make strong (specification) claims.
So maybe this comes down to the linker supporting a subset ABI's data types,
and that subset might increase over time, but never decrease? In this respect
could we present a table for each supported linker ABI listing the ABI type and
its canonical layout type? (in practice it might just be one table with noted
adjustments.)
Then there is the possibility that a linker might change the layout
corresponding to a data type. Ideally the linker support the prior layout *and*
the new layout. I don't think this will arise with the current support set of
supported ABI data types, but it might if we choose to add support for say the
optional `__int128` data type prior to the platform adding support for a
primitive value class of Int128?
[1] https://gitlab.com/x86-psABIs/x86-64-ABI
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PR Review: https://git.openjdk.org/jdk/pull/14037#pullrequestreview-1431762962
