Hacker News new | past | comments | ask | show | jobs | submit login

"every command in C will give you a deterministic amount of commands in assembly"

This is most definitely not true on any modern compiler. The generated assembly depends on the program as a whole and may not correspond fragment to fragment in any readily comprehensible way.

One example is a variable in C may correspond to a number of different storage locations at different points in the program graph, owing to SSA form (or individual optimizations that transform the program in a similar manner).

Another example is how pointer aliasing affects generated code: copying arguments into temporaries before arithmetic can actually result in fewer assembly instructions as the compiler can determine no aliasing is possible.

Add to this the more mundane and well understood optimizations like inlining, constant propagation, later passes of optimizations over the results of the prior and the result is that it's very hard to know exactly what assembly will correspond to any arbitrary part of a c program. Mapping memory locations to variables or assembly instructions to c program lines is not trivial.

I know this seems like nitpicking, but programmers using the mistaken mental model of c being textual macros for assembly leads to poorly performing code at best, and a variety of security vulnerabilities at worst. I think if you actually need to know what's going on at the machine level it's very important to know that the c abstract machine is most definitely NOT what the real machine on your desk is doing.




Also, like the article mentions, it has abstractions that you can't get rid of, like the stack.




Consider applying for YC's W25 batch! Applications are open till Nov 12.

Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: