[foreign-memaccess+abi] RFR: 8308293: A linker should expose the layouts it supports

[Jorn Vernee]

On Thu, 15 Jun 2023 16:30:23 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> I'm not too sure on what this shared factories would look like. In the general case (e.g. fallback) it would have at least to specify the size of short/int/long/long long. Plus possibly, size_t. Basically everything besides float/double/char/bool. I'm not sure that would end up simpler than just having duplicated code with the layout creation?
>
> For the fallback linker I agree, but for the other platforms, it seems that only the layout of `long` and `size_t` changes? I was thinking something like:
> 
> 
> static Map<String, MemoryLayout> makeCanonicalLayouts(ValueLayout longLayout, ValueLayout sizeTLayout) {
>     return Map.ofEntries(
>             // specified canonical layouts
>             Map.entry("bool", ValueLayout.JAVA_BOOLEAN),
>             Map.entry("char", ValueLayout.JAVA_BYTE),
>             Map.entry("short", ValueLayout.JAVA_SHORT),
>             Map.entry("int", ValueLayout.JAVA_INT),
>             Map.entry("float", ValueLayout.JAVA_FLOAT),
>             Map.entry("long", longLayout),
>             Map.entry("long long", ValueLayout.JAVA_LONG),
>             Map.entry("double", ValueLayout.JAVA_DOUBLE),
>             Map.entry("void*", ValueLayout.ADDRESS),
>             Map.entry("size_t", sizeTLayout),
>             // unspecified size-dependent layouts
>             Map.entry("int8_t", ValueLayout.JAVA_BYTE),
>             Map.entry("int16_t", ValueLayout.JAVA_SHORT),
>             Map.entry("int32_t", ValueLayout.JAVA_INT),
>             Map.entry("int64_t", ValueLayout.JAVA_LONG),
>             // unspecified JNI layouts
>             Map.entry("jboolean", ValueLayout.JAVA_BOOLEAN),
>             Map.entry("jchar", ValueLayout.JAVA_CHAR),
>             Map.entry("jbyte", ValueLayout.JAVA_BYTE),
>             Map.entry("jshort", ValueLayout.JAVA_SHORT),
>             Map.entry("jint", ValueLayout.JAVA_INT),
>             Map.entry("jlong", ValueLayout.JAVA_LONG),
>             Map.entry("jfloat", ValueLayout.JAVA_FLOAT),
>             Map.entry("jdouble", ValueLayout.JAVA_DOUBLE)
>     );
> }
> 
> 
> Then each linker can have:
> 
> 
> private static final ValueLayout C_LONG = ...
> private static final ValueLayout C_SIZE_T = ...
> private static final Map<String, MemoryLayout> CANONICAL_LAYOUTS_MAP = SharedUtils.makeCanonicalLayouts(C_LONG, C_SIZE_T);
> 
> @Override
> public Map<String, MemoryLayout> canonicalLayouts() {
>     return CANONICAL_LAYOUTS_MAP;
>  }

And then the fallback linker could do it's own thing.

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/839#discussion_r1231276930