miri: fix overflow detection for unsigned pointer offset #130239
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Some changes occurred to the CTFE / Miri engine cc @rust-lang/miri The Miri subtree was changed cc @rust-lang/miri |
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@bors r+ rollup |
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… r=compiler-errors miri: fix overflow detection for unsigned pointer offset This is the Miri part of rust-lang#130229. This is already UB in codegen so we better make Miri detect it; updating the docs may take time if we have to follow some approval process, but let's make Miri match reality ASAP. r? `@scottmcm`
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…kingjubilee Rollup of 11 pull requests Successful merges: - rust-lang#119286 (show linker output even if the linker succeeds) - rust-lang#129103 (Don't warn empty branches unreachable for now) - rust-lang#129696 (update stdarch) - rust-lang#129835 (enable const-float-classify test, and test_next_up/down on 32bit x86) - rust-lang#129992 (Update compiler-builtins to 0.1.125) - rust-lang#130052 (Don't leave debug locations for constants sitting on the builder indefinitely) - rust-lang#130077 (Fix linking error when compiling for 32-bit watchOS) - rust-lang#130114 (Remove needless returns detected by clippy in the compiler) - rust-lang#130156 (Add test for S_OBJNAME & update test for LF_BUILDINFO cl and cmd) - rust-lang#130168 (maint: update docs for change_time ext and doc links) - rust-lang#130239 (miri: fix overflow detection for unsigned pointer offset) r? `@ghost` `@rustbot` modify labels: rollup
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…kingjubilee Rollup of 10 pull requests Successful merges: - rust-lang#129103 (Don't warn empty branches unreachable for now) - rust-lang#129696 (update stdarch) - rust-lang#129835 (enable const-float-classify test, and test_next_up/down on 32bit x86) - rust-lang#130077 (Fix linking error when compiling for 32-bit watchOS) - rust-lang#130114 (Remove needless returns detected by clippy in the compiler) - rust-lang#130168 (maint: update docs for change_time ext and doc links) - rust-lang#130228 (notify Miri when intrinsics are changed) - rust-lang#130239 (miri: fix overflow detection for unsigned pointer offset) - rust-lang#130244 (Use the same span for attributes and Try expansion of ?) - rust-lang#130248 (Limit `libc::link` usage to `nto70` target only, not NTO OS) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#130239 - RalfJung:miri-ptr-offset-unsigned, r=compiler-errors miri: fix overflow detection for unsigned pointer offset This is the Miri part of rust-lang#130229. This is already UB in codegen so we better make Miri detect it; updating the docs may take time if we have to follow some approval process, but let's make Miri match reality ASAP. r? ``@scottmcm``
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…ottmcm ptr::add/sub: do not claim equivalence with `offset(c as isize)` In rust-lang#110837, the `offset` intrinsic got changed to also allow a `usize` offset parameter. The intention is that this will do an unsigned multiplication with the size, and we have UB if that overflows -- and we also have UB if the result is larger than `usize::MAX`, i.e., if a subsequent cast to `isize` would wrap. ~~The LLVM backend sets some attributes accordingly.~~ This updates the docs for `add`/`sub` to match that intent, in preparation for adjusting codegen to exploit this UB. We use this opportunity to clarify what the exact requirements are: we compute the offset using mathematical multiplication (so it's no problem to have an `isize * usize` multiplication, we just multiply integers), and the result must fit in an `isize`. Cc `@rust-lang/opsem` `@nikic` rust-lang#130239 updates Miri to detect this UB. `sub` still has some cases of UB not reflected in the underlying intrinsic semantics (and Miri does not catch): when we subtract `usize::MAX`, then after casting to `isize` that's just `-1` so we end up adding one unit without noticing any UB, but actually the offset we gave does not fit in an `isize`. Miri will currently still not complain for such cases: ```rust fn main() { let x = &[0i32; 2]; let x = x.as_ptr(); // This should be UB, we are subtracting way too much. unsafe { x.sub(usize::MAX).read() }; } ``` However, the LLVM IR we generate here also is UB-free. This is "just" library UB but not language UB. Cc `@saethlin;` might be worth adding precondition checks against overflow on `offset`/`add`/`sub`? Fixes rust-lang#130211
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Rollup merge of rust-lang#130229 - RalfJung:ptr-offset-unsigned, r=scottmcm ptr::add/sub: do not claim equivalence with `offset(c as isize)` In rust-lang#110837, the `offset` intrinsic got changed to also allow a `usize` offset parameter. The intention is that this will do an unsigned multiplication with the size, and we have UB if that overflows -- and we also have UB if the result is larger than `usize::MAX`, i.e., if a subsequent cast to `isize` would wrap. ~~The LLVM backend sets some attributes accordingly.~~ This updates the docs for `add`/`sub` to match that intent, in preparation for adjusting codegen to exploit this UB. We use this opportunity to clarify what the exact requirements are: we compute the offset using mathematical multiplication (so it's no problem to have an `isize * usize` multiplication, we just multiply integers), and the result must fit in an `isize`. Cc `@rust-lang/opsem` `@nikic` rust-lang#130239 updates Miri to detect this UB. `sub` still has some cases of UB not reflected in the underlying intrinsic semantics (and Miri does not catch): when we subtract `usize::MAX`, then after casting to `isize` that's just `-1` so we end up adding one unit without noticing any UB, but actually the offset we gave does not fit in an `isize`. Miri will currently still not complain for such cases: ```rust fn main() { let x = &[0i32; 2]; let x = x.as_ptr(); // This should be UB, we are subtracting way too much. unsafe { x.sub(usize::MAX).read() }; } ``` However, the LLVM IR we generate here also is UB-free. This is "just" library UB but not language UB. Cc `@saethlin;` might be worth adding precondition checks against overflow on `offset`/`add`/`sub`? Fixes rust-lang#130211
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This is the Miri part of #130229. This
is already UBis planned to become UB in codegen so we better make Miri detect it; updating the docs may take time if we have to follow some approval process, but let's make Miri match reality ASAP.r? @scottmcm