Update for -fPIC bug

Author: brson

_posts/2017-02-09-Rust-1.15.1.md

@@ -22,10 +22,23 @@ appropriate page on our website, and check out the [detailed release notes for
 
 ### What's in 1.15.1 stable
 
-This release fixes a single issue, a soundness bug in the new
-`vec::IntoIter::as_mut_slice` method. The problem with this three line function
-was [discovered] just minutes after publishing Rust 1.15.0, and is a reminder
-that writing unsafe code is hard.
+This release fixes two issues, a soundness bug in the new
+`vec::IntoIter::as_mut_slice` method, and a regression wherein certain C
+components of the Rust distribution were [not compiled with `-fPIC`][fpic].  The
+latter results in the text section of executables being writable in some
+configurations, including common Linux configurations, subverting an important
+attack mitigation, and causing longer startup times by causing the linker to do
+more work. For mostly-Rust codebases, the practical impact of losing read-only
+text sections is relatively small (since Rust's type system is its first line of
+defense), but for Rust linked into other codebases the impact could be
+unexpectedly quite significant. The details of the bug are not that interesting
+though, and rest of this post focuses on the former soundness bug.
+
+[fpic]: https://github.com/rust-lang/rust/pull/39523
+
+The problem with `as_mut_slice`, a three line function, was [discovered] just
+minutes after publishing Rust 1.15.0, and is a reminder that writing unsafe code
+is hard.
 
 [discovered]: https://www.reddit.com/r/rust/comments/5roiq7/announcing_rust_115/dd8vujs/