miri: accept extern types in structs if they are the only field #55672

RalfJung · 2018-11-04T10:24:20Z

Fixes #55541

Cc @oli-obk @eddyb #43467

rust-highfive · 2018-11-04T10:24:23Z

r? @varkor

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eddyb · 2018-11-04T10:35:12Z

I would prefer it if this was based on offset being 0, not field count.

RalfJung · 2018-11-04T10:55:24Z

Like this?

src/test/ui/consts/const-eval/issue-55541.rs

eddyb · 2018-11-04T13:33:38Z

I'm not sure the alignment condition is needed, since 0 is aligned to infinity, but I don't think it hurts.

eddyb · 2018-11-04T14:15:33Z

src/librustc_mir/interpret/place.rs

@@ -354,7 +354,8 @@ where
        let (meta, offset) = if field_layout.is_unsized() {
            // re-use parent metadata to determine dynamic field layout
            let (_, align) = self.size_and_align_of(base.meta, field_layout)?
-                .expect("Fields cannot be extern types");
+                // If this is an extern type, we fall back to its static size and alignment.
+                .unwrap_or_else(|| base.layout.size_and_align());


Interestingly, we can make size_and_align_of error, but have a separate align_of that works even for extern type. Only the alignment is used here, anyway!

Oh, you can also just move the Option to be around the size, but not the alignment.

I could, but I'd rather wait for the decision to treat the size_of_val and align_of_val intrinsics asymmetrically before doing that.

extern type will likely get alignment 1 currently, which is likely not actually correct for the type they are opaquely representing, so I am a bit worried about unilaterally implementing such behavior.

You can't access that alignment without first having a reference, so having it too high would be a problem (the assumption might not be guaranteed by what you're FFI-ing to), but having it too low wouldn't break anything (other than field offsets).

So the way I see it, the alignment is only a lower bound, and 1 is fine, unless you want to use it as an aligned field in a struct.

Anyway, my concern is also kind of a confusing code thing.
You could also add a .map(|(_, align)| align) before unwrap_or_else, which would mean the code and the comment wouldn't mention the "size" of the extern type.

You can't access that alignment without first having a reference, so having it too high would be a problem (the assumption might not be guaranteed by what you're FFI-ing to), but having it too low wouldn't break anything (other than field offsets).

Oh that's a good point. We cannot create such references ourselves anyway as we cannot have data of that type.

Still I think miri shouldn't move ahead of the rest of the decision process here.

I will implement your map suggestion.

I implemented what you suggested.

eddyb · 2018-11-05T10:22:59Z

@bors r+

bors · 2018-11-05T10:23:00Z

📌 Commit a6622c2 has been approved by eddyb

RalfJung · 2018-11-05T20:04:57Z

src/librustc_mir/interpret/place.rs

+                // FIXME: Once we have made decisions for how to handle size and alignment
+                // of `extern type`, this should be adapted.  It is just a temporary hack
+                // to get some code to work that probably ought to work.
+                .unwrap_or_else(|| base.layout.align);


Should this really be base.layout, not field_layout?

RalfJung · 2018-11-05T20:05:06Z

Hm actually I am not entirely sure I got this right, will this error out appropriately when there are other fields? It will error out in size_and_align_of, but what about mplace_field? It does not do any such check.

eddyb · 2018-11-05T21:14:33Z

@RalfJung Ah, yeah, you probably want it in both. This is why decoupling alignment from size should help - size and offset computation are similar/equivalent, whereas alignment is simpler.

RalfJung · 2018-11-06T07:30:42Z

Offset computation of a field only uses the field's alignment, though (and the offsets data in the layout).

RalfJung · 2018-11-06T07:42:31Z

I fixed that, I think.

eddyb · 2018-11-06T08:11:44Z

@bors r+

bors · 2018-11-06T08:11:45Z

📌 Commit ba0bab3 has been approved by eddyb

bors · 2018-11-16T17:16:51Z

⌛ Testing commit ba0bab3 with merge b2282c6f23a0d1c0e850f6cf871e5cbe8b1985f9...

bors · 2018-11-16T19:32:11Z

💔 Test failed - status-appveyor

RalfJung · 2018-11-16T20:44:03Z

It's that timing test again:

failures:
    time::tests::instant_math

@bors retry

@rust-lang/infra maybe the permitted time difference should be increased to 500ms or so?

@oli-obk

miri: accept extern types in structs if they are the only field Fixes rust-lang#55541 Cc @oli-obk @eddyb rust-lang#43467

bors · 2018-11-17T21:48:11Z

⌛ Testing commit ba0bab3 with merge 54966b13b4f4b6d5d168c952194b6f9e2e73551b...

bors · 2018-11-17T23:28:49Z

💔 Test failed - status-appveyor

kennytm · 2018-11-18T04:06:56Z

@bors retry

error: failed to remove file `C:\projects\rust\build\x86_64-pc-windows-msvc\stage2-tools\x86_64-pc-windows-msvc\cit\t989\foo\target\release\libfoo.rmeta`
Caused by:
  Access is denied. (os error 5)

bors · 2018-11-18T22:20:00Z

⌛ Testing commit ba0bab3 with merge a9b791b...

@oli-obk

miri: accept extern types in structs if they are the only field Fixes #55541 Cc @oli-obk @eddyb #43467

bors · 2018-11-19T01:08:23Z

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing a9b791b to master...

miri: accept extern types in structs if they are the only field

e753d21

rust-highfive assigned varkor Nov 4, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 4, 2018

test for offset and alignment of the sized part, instead of field count

aca76d4

RalfJung force-pushed the miri-extern-types branch from aa34f15 to aca76d4 Compare November 4, 2018 10:55

eddyb reviewed Nov 4, 2018

View reviewed changes

src/test/ui/consts/const-eval/issue-55541.rs Show resolved Hide resolved

also test with PhantomData

bb17f71

eddyb reviewed Nov 4, 2018

View reviewed changes

make it more obvious that the size is not relevant

5ebd077

RalfJung mentioned this pull request Nov 5, 2018

Tracking issue for RFC 1861: Extern types #43467

Open

7 tasks

note some FIXMEs

a6622c2

eddyb approved these changes Nov 5, 2018

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 5, 2018

RalfJung commented Nov 5, 2018

View reviewed changes

make sure we only guess field alignment at offset 0

ba0bab3

RalfJung added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 6, 2018

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 16, 2018

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 16, 2018

kennytm added a commit to kennytm/rust that referenced this pull request Nov 17, 2018

Rollup merge of rust-lang#55672 - RalfJung:miri-extern-types, r=eddyb

0c5947a

miri: accept extern types in structs if they are the only field Fixes rust-lang#55541 Cc @oli-obk @eddyb rust-lang#43467

kennytm mentioned this pull request Nov 17, 2018

Rollup of 17 pull requests #56026

Closed

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 17, 2018

kennytm mentioned this pull request Nov 18, 2018

Spurious error in time::tests::instant_math on Windows #56034

Closed

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 18, 2018

kennytm mentioned this pull request Nov 18, 2018

Spurious failure "failed to remove file ... Access is denied" in cargo test profile_selection_check_all_targets* on Windows #56040

Closed

bors added a commit that referenced this pull request Nov 18, 2018

Auto merge of #55672 - RalfJung:miri-extern-types, r=eddyb

a9b791b

miri: accept extern types in structs if they are the only field Fixes #55541 Cc @oli-obk @eddyb #43467

bors merged commit ba0bab3 into rust-lang:master Nov 19, 2018

kennytm mentioned this pull request Nov 20, 2018

Spurious 30 minutes timeout on Travis CI #56112

Closed

RalfJung deleted the miri-extern-types branch November 30, 2018 08:28

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miri: accept extern types in structs if they are the only field #55672

miri: accept extern types in structs if they are the only field #55672

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miri: accept extern types in structs if they are the only field #55672

miri: accept extern types in structs if they are the only field #55672

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