[foreign] RFR: record padding is not emitted correctly

[Henry Jen]

I believe in getRecordLayoutInternal, line 353, stream filter should use cx.isAnonymous rather than cx.isAnonymousStruct, as an anonymous union can be embedded in a struct.

Otherwise, seems good to me. I’ll do some testing later.

Cheers,
Henry

> On Jun 14, 2018, at 7:37 AM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> Hi,
> this is an overhaul of how jextract adds padding to record layouts - the general strategy is this:
> 
> 1) make sure that fields are emitted at the correct expected offset, if not , add prefix padding
> 2) make sure that record size matches the expected one, if not add trailing padding
> 
> Note that (1) should onlyy apply to structs, not unions, as for unions, you always restart from the base offset for each field; so, assumption is, base offset should already be in sync because of outer padding (if needed).
> 
> To get there, the Utils::getRecordLayoutInternal now does a recursive walk, as anonymous nested records must join the dance too.
> 
> I also did a followup fix on the patch that Sundar sent yesterday; in short, using Utils:getIdentifier doesn't always work. For typedefs it does the right thing, but for anonymous records it just gives a random blob of text mentioning the source location; I tweaked this so that if I see that the output contains '::', I generate a synthetic string "anon$xyz", where xyz is the offset in the source for that anon record.
> 
> 
> I also noted that when structs contain incomplete arrays (e.g.flexible array members), clang fails to return correct offset for anything inside the struct, and returns -2 instead. Right now I'm accepting it (as did the old impl, and the one in the nicl branch), but I believe it would be better to punt with an exception (after all the generated layout will be all wrong) - but if I do so, the StructTest, which contains an incomplete array, will fail. Opinions?
> 
> Webrev:
> 
> http://cr.openjdk.java.net/~mcimadamore/panama/padding_layout/
> 
> Cheers
> Maurizio
>