afa1dddcf9
Previously, Item was a struct of a NonZeroU64, an Option which was usually unset or irrelevant, and a 4-variant enum. So collectively, the size of an Item was 24 bytes, but only 8 bytes were used for the most part. So this takes advantage of the fact that it is probably impossible to exhaust the total space of SbTags, and steals 3 bits from it to pack the whole struct into a single u64. This bit-packing means that we reduce peak memory usage when Miri goes memory-bound by ~3x. We also get CPU performance improvements of varying size, because not only are we simply accessing less memory, we can now compare a Vec<Item> using a memcmp because it does not have any padding.
41 lines
1.5 KiB
Plaintext
41 lines
1.5 KiB
Plaintext
error: Undefined Behavior: not granting access to tag <TAG> because incompatible item is protected: [Unique for <TAG>] (call ID)
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--> $DIR/illegal_write6.rs:LL:CC
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LL | unsafe { *y = 2 };
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| ^^^^^^ not granting access to tag <TAG> because incompatible item is protected: [Unique for <TAG>] (call ID)
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= help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
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= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
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help: <TAG> was created by a retag at offsets [0x0..0x4]
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--> $DIR/illegal_write6.rs:LL:CC
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LL | let p = x as *mut u32;
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| ^
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help: <TAG> was protected due to <TAG> which was created here
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--> $DIR/illegal_write6.rs:LL:CC
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LL | foo(x, p);
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| ^
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help: this protector is live for this call
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--> $DIR/illegal_write6.rs:LL:CC
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LL | / fn foo(a: &mut u32, y: *mut u32) -> u32 {
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LL | | *a = 1;
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LL | | let _b = &*a;
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LL | | unsafe { *y = 2 };
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LL | | return *a;
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LL | | }
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| |_^
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= note: backtrace:
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= note: inside `foo` at $DIR/illegal_write6.rs:LL:CC
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note: inside `main` at $DIR/illegal_write6.rs:LL:CC
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--> $DIR/illegal_write6.rs:LL:CC
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LL | foo(x, p);
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| ^^^^^^^^^
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note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
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error: aborting due to previous error
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