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[breaking change] Disallow statics initializing themselves #71140

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Merged
merged 3 commits into from
Apr 26, 2020
Merged

[breaking change] Disallow statics initializing themselves #71140

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2b25c0c
Don't load the same allocation twice when reading a scalar pair from it
oli-obk Apr 14, 2020
af44cdf
Disallow statics initializing themselves
oli-obk Apr 23, 2020
e4ab4ee
Update src/librustc_mir/interpret/memory.rs
oli-obk Apr 23, 2020
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Disallow statics initializing themselves
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@oli-obk
oli-obk committed Apr 23, 2020
commit af44cdf04fddf4d18efee49c0c683cb4bbce71fa
11 changes: 10 additions & 1 deletion src/librustc_mir/interpret/memory.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,16 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {

// We can still be zero-sized in this branch, in which case we have to
// return `None`.
if size.bytes() == 0 { None } else { Some(ptr) }
if size.bytes() == 0 {
// We may be reading from a static.
// In order to ensure that `static FOO: Type = FOO;` causes a cycle error
// instead of magically pulling *any* ZST value from the ether, we need to
// trigger a read here.
self.get_raw(ptr.alloc_id)?;
None
} else {
Some(ptr)
}
}
})
}
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8 changes: 6 additions & 2 deletions src/test/ui/consts/recursive-zst-static.rs
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@@ -1,6 +1,10 @@
// build-pass
// This test ensures that we do not allow ZST statics to initialize themselves without ever
// actually creating a value of that type. This is important, as the ZST may have private fields
// that users can reasonably expect to only get initialized by their own code. Thus unsafe code
// can depend on this fact and will thus do unsound things when it is violated.
// See https://github.com/rust-lang/rust/issues/71078 for more details.

static FOO: () = FOO;
static FOO: () = FOO; //~ cycle detected when const-evaluating `FOO`

fn main() {
FOO
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21 changes: 21 additions & 0 deletions src/test/ui/consts/recursive-zst-static.stderr
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@@ -0,0 +1,21 @@
error[E0391]: cycle detected when const-evaluating `FOO`
--> $DIR/recursive-zst-static.rs:7:18
|
LL | static FOO: () = FOO;
| ^^^
|
note: ...which requires const-evaluating `FOO`...
--> $DIR/recursive-zst-static.rs:7:1
|
LL | static FOO: () = FOO;
| ^^^^^^^^^^^^^^^^^^^^^
= note: ...which again requires const-evaluating `FOO`, completing the cycle
note: cycle used when const-evaluating + checking `FOO`
--> $DIR/recursive-zst-static.rs:7:1
|
LL | static FOO: () = FOO;
| ^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0391`.