Document that CFI diverges from Rust wrt. ABI-compatibility rules#155361
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Darksonn wants to merge 8 commits intorust-lang:mainfrom
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Document that CFI diverges from Rust wrt. ABI-compatibility rules#155361Darksonn wants to merge 8 commits intorust-lang:mainfrom
Darksonn wants to merge 8 commits intorust-lang:mainfrom
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RalfJung
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Apr 16, 2026
This was too confusing. This section is about Rust-to-Rust calls, so it sounds like it's referring to how core::ffi::c_int and similar behave, but that is not the case (it's about how C does it, which differs from what core::ffi::c_int does), and either way it is off-topic for Rust-to-Rust calls.
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The CFI sanitizer is a sanitizer that checks that no ABI-incompatible function calls are made at runtime, but there is currently an unfortunate divergence between the Rust ABI-compatibility rules and what the CFI sanitizer checks. Thus, document that this divergence exists.
There are proposals for how we can align the ABI rules to eliminate this discrepancy, and I would like to follow through with those, but for now I think we can at least document that the discrepancy exists.
For further discussion please see Re-evaluate ABI compatibility rules in light of CFI and Can CFI be made compatible with type erasure schemes? and
fn_cast!macro.cc @rcvalle @samitolvanen @maurer @bjorn3 @RalfJung
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