From: Ralf Jung Date: Thu, 26 Jul 2018 16:35:39 +0000 (+0200) Subject: link to miri pointer def.n X-Git-Url: https://git.ralfj.de/web.git/commitdiff_plain/23be7cd840fba9c0646492d61398492c335a8105?ds=sidebyside link to miri pointer def.n --- diff --git a/ralf/_posts/2018-07-24-pointers-and-bytes.md b/ralf/_posts/2018-07-24-pointers-and-bytes.md index 85ba4aa..8f7089e 100644 --- a/ralf/_posts/2018-07-24-pointers-and-bytes.md +++ b/ralf/_posts/2018-07-24-pointers-and-bytes.md @@ -119,7 +119,7 @@ C++ and Rust employ a more "high-level" view of memory and pointers, restricting When formally describing what the programmer may and may not do in these languages, as we have seen, the model of pointers as integers falls apart, so we have to look for something else. This is another example of using a "virtual machine" that's different from the real machine for specification purposes, which is an idea [I have blogged about before]({% post_url 2017-06-06-MIR-semantics %}). -Here's a simple proposal (in fact, this is the model of pointers used in [CompCert](https://hal.inria.fr/hal-00703441/document) and my [RustBelt work]({% post_url 2017-07-08-rustbelt %}), and it is also how [miri](https://github.com/solson/miri/) implements pointers): +Here's a simple proposal (in fact, this is the model of pointers used in [CompCert](https://hal.inria.fr/hal-00703441/document) and my [RustBelt work]({% post_url 2017-07-08-rustbelt %}), and it is also how [miri](https://github.com/solson/miri/) implements [pointers](https://github.com/rust-lang/rust/blob/fefe81605d6111faa8dbb3635ab2c51d59de740a/src/librustc/mir/interpret/mod.rs#L121-L124)): A pointer is a pair of some kind of ID uniquely identifying the *allocation*, and an *offset* into the allocation. Adding/subtracting an integer to/from a pointer just acts on the offset, and can thus never leave the allocation. Subtracting a pointer from another is only allowed when both point to the same allocation (matching [C++](https://timsong-cpp.github.io/cppwp/n4140/expr.add#6)).[^2]