blog: Assume we will never have a non-empty baseurl

[web.git] / ralf / _posts / 2018-07-24-pointers-and-bytes.md

diff --git a/ralf/_posts/2018-07-24-pointers-and-bytes.md b/ralf/_posts/2018-07-24-pointers-and-bytes.md
index 05690b3a6e3fb88860c4adb39025f7b605b30cde..dfd6bd1cfc1186d61cd74074ac9f84e6a5f47e08 100644 (file)
--- a/ralf/_posts/2018-07-24-pointers-and-bytes.md
+++ b/ralf/_posts/2018-07-24-pointers-and-bytes.md
@@ -4,7 +4,7 @@ categories: internship rust
 forum: https://internals.rust-lang.org/t/pointers-are-complicated-or-whats-in-a-byte/8045
 ---
 
-This summer, I am again [working on Rust full-time]({{ site.baseurl }}{% post_url 2018-07-11-research-assistant %}), and again I will work (amongst other things) on a "memory model" for Rust/MIR.
+This summer, I am again [working on Rust full-time]({% post_url 2018-07-11-research-assistant %}), and again I will work (amongst other things) on a "memory model" for Rust/MIR.
 However, before I can talk about the ideas I have for this year, I have to finally take the time and dispel the myth that "pointers are simple: they are just integers".
 Both parts of this statement are false, at least in languages with unsafe features like Rust or C: Pointers are neither simple nor (just) integers.
 
@@ -38,7 +38,7 @@ However, given how low-level a language C++ is, we can actually break this assum
 Since `&x[i]` is the same as `x+i`, this means we are actually writing `23` to `&y[0]`.
 
 Of course, that does not stop C++ compilers from doing these optimizations.
-To allow this, the standard declares our code to have [undefined behavior]({{ site.baseurl }}{% post_url 2017-07-14-undefined-behavior %}).
+To allow this, the standard declares our code to have [undefined behavior]({% post_url 2017-07-14-undefined-behavior %}).
 
 First of all, it is not allowed to perform pointer arithmetic (like `&x[i]` does) that goes [beyond either end of the array it started in](https://timsong-cpp.github.io/cppwp/n4140/expr.add#5).
 Our program violates this rule: `x[i]` is outside of `x`, so this is undefined behavior.
@@ -117,9 +117,9 @@ But the actual machine also does not do the kind of optimizations that modern C+
 If we wrote the above programs in assembly, there would be no UB, and no optimizations.
 C++ and Rust employ a more "high-level" view of memory and pointers, restricting the programmer for the benefit of optimizations.
 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]({{ site.baseurl }}{% post_url 2017-06-06-MIR-semantics %}).
+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]({{ site.baseurl }}{% 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):
 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]