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remove the memcpy-on-equal-ptrs assumption #118265

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Merged
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Nov 29, 2023
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remove the memcpy-on-equal-ptrs assumption #118265

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5 changes: 2 additions & 3 deletions library/core/src/lib.rs
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Expand Up @@ -24,9 +24,8 @@
//! which are generated by Rust codegen backends. Additionally, this library can make explicit
//! calls to `strlen`. Their signatures are the same as found in C, but there are extra
//! assumptions about their semantics: For `memcpy`, `memmove`, `memset`, `memcmp`, and `bcmp`, if
//! the `n` parameter is 0, the function is assumed to not be UB. Furthermore, for `memcpy`, if
//! source and target pointer are equal, the function is assumed to not be UB.
//! (Note that these are standard assumptions among compilers:
//! the `n` parameter is 0, the function is assumed to not be UB, even if the pointers are NULL or
//! dangling. (Note that making extra assumptions about these functions is common among compilers:
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While removing the "equal" part, you added "NULL or dangling" -- isn't that a new assumption? Or are we already living by that elsewhere?

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That's a clarification. We already have "if the n parameter is 0, the function is assumed to not be UB", which was already meant to include all pointers, including NULL or dangling. I just made it more explicit.

//! [clang](https://reviews.llvm.org/D86993) and [GCC](https://gcc.gnu.org/onlinedocs/gcc/Standards.html#C-Language) do the same.)
//! These functions are often provided by the system libc, but can also be provided by the
//! [compiler-builtins crate](https://crates.io/crates/compiler_builtins).
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