refactor: reorder examples and validation sections

[web.git] / personal / _posts / 2017-07-14-undefined-behavior.md

diff --git a/personal/_posts/2017-07-14-undefined-behavior.md b/personal/_posts/2017-07-14-undefined-behavior.md
index ae5463e70cffd98b73a46cb54495a436893f26b8..77e73151c18cbd644430cc8bbc883eeb8829bca0 100644 (file)
--- a/personal/_posts/2017-07-14-undefined-behavior.md
+++ b/personal/_posts/2017-07-14-undefined-behavior.md
@@ -39,7 +39,7 @@ This could be the end of the game:  No alias information, no way to verify our a
 
 ## Shifting responsibility
 
 
 ## Shifting responsibility
 

-However, it turns out that compilers writers consider these optimizations important enough that they came up with an alternative solution:
+However, it turns out that compiler writers consider these optimizations important enough that they came up with an alternative solution:

 Instead of having the compiler verify such assumptions, they declared the programmer responsible.
 
 For example, the C standard says that memory accesses have to happen with the right "effective type":  If data was stored with a `float` pointer, it must not be read with an `int` pointer.
 Instead of having the compiler verify such assumptions, they declared the programmer responsible.
 
 For example, the C standard says that memory accesses have to happen with the right "effective type":  If data was stored with a `float` pointer, it must not be read with an `int` pointer.


@@ -55,7 +55,7 @@ Undefined behavior moves the burden of proving the correctness of this optimizat
 Considering that the compiler can only be so smart, this is a great way to justify optimizations that would otherwise be difficult or impossible to perform.
 Unfortunately, it is often not easy to say whether a program has undefined behavior or not -- after all, such an analysis being difficult is the entire reason compilers have to rely on UB to perform their optimizations.
 Furthermore, while C compilers are happy to exploit the fact that a particular program *has* UB, they do not provide a way to test that executing a program *does not* trigger UB.
 Considering that the compiler can only be so smart, this is a great way to justify optimizations that would otherwise be difficult or impossible to perform.
 Unfortunately, it is often not easy to say whether a program has undefined behavior or not -- after all, such an analysis being difficult is the entire reason compilers have to rely on UB to perform their optimizations.
 Furthermore, while C compilers are happy to exploit the fact that a particular program *has* UB, they do not provide a way to test that executing a program *does not* trigger UB.

-It also turns out that programmers' intuition often [does not match what the compiler does](https://www.cl.cam.ac.uk/~pes20/cerberus/notes50-survey-discussion.html), which leads to miscompilations (in the eye of the programmer) and sometimes to security [vulerabilities](https://lwn.net/Articles/342330/).
+It also turns out that programmers' intuition often [does not match what the compiler does](https://www.cl.cam.ac.uk/~pes20/cerberus/notes50-survey-discussion.html), which leads to miscompilations (in the eye of the programmer) and sometimes to security [vulnerabilities](https://lwn.net/Articles/342330/).

 As a consequence, UB has a pretty bad reputation.
 
 There are various sanitizers that watch a program while it is being executed and try to detect UB, but they are not able to catch all possible sources of UB.
 As a consequence, UB has a pretty bad reputation.
 
 There are various sanitizers that watch a program while it is being executed and try to detect UB, but they are not able to catch all possible sources of UB.


@@ -87,4 +87,6 @@ Such a specification would describe the additional state that is needed at run-t
 It is with such considerations in my mind that I have previously written about [miri as an executable specification]({{ site.baseurl }}{% post_url 2017-06-06-MIR-semantics %}).
 
 Coming up next on this channel:  During my [internship]({{ site.baseurl }}{% post_url 2017-05-23-internship-starting %}), I am working on such a specification.
 It is with such considerations in my mind that I have previously written about [miri as an executable specification]({{ site.baseurl }}{% post_url 2017-06-06-MIR-semantics %}).
 
 Coming up next on this channel:  During my [internship]({{ site.baseurl }}{% post_url 2017-05-23-internship-starting %}), I am working on such a specification.

-I have a draft ready now, and I want to share it with the world to see what the world thinks about it.
+My ideas are concrete enough now that I can write down a draft, which I will share with the world to see what the world thinks about it.
+
+**Uodate:** [Writing down has happened]({{ site.baseurl }}{% post_url 2017-07-17-types-as-contracts %}).