DmitrySoshnikov

/**
 * Stack buffer overflow.
 *
 * TL;DR: In older OSes, a buffer overflow of the data on the stack
 * allowed overriding a return address, and execute an exploit code,
 * instead of returning to a caller.
 *
 * Docs: https://en.wikipedia.org/wiki/Stack_buffer_overflow
 *
 * by Dmitry Soshnikov <[email protected]>

DmitrySoshnikov

(*
 * "Essentials of interpretation. Semantics of programming languages"
 *
 * Lesson 1: Arithmetic expressions evaluator.
 *
 * BNF grammar:
 *
 *   NUMBER -> \d+
 *
 *   Exp -> NUMBER

DmitrySoshnikov

x86: More code - less code

Sometimes more code in a source language, can mean less code in a generated language.

NOTE: below we used gcc 5.3 with -std=c++14 -O3 flags.

On the example of C programming language, and its translation to x64 assembly, let's take a look at the following example:

// 7 times `x`.

DmitrySoshnikov

/**
 * Contiguous and non-contiguous C-arrays allocation in memory.
 * by Dmitry Soshnikov <[email protected]>
 */

#include <iostream>

int main()
{
    // -----------------------------

DmitrySoshnikov

/**
 * S-expression parser
 *
 * Recursive descent parser of a simplified sub-set of s-expressions.
 * 
 * NOTE: the format of the programs is used in the "Essentials of interpretation"
 * course: https://github.com/DmitrySoshnikov/Essentials-of-interpretation
 *
 * Grammar:
 *

DmitrySoshnikov

Addressing modes in mov, and their C version

Below are addressing modes (immediate, register, memory) on the examples of the mov assembly instruction. Here we use movl ("move long") for a 32-bit word.

Note: cannot move memory-to-memory, need two instructions.

Src

movl

DmitrySoshnikov

/**
 * "Is connected?"
 *
 * Dynamic connectivity issue.
 *
 *    1  2:  not connected
 *    1--2:  connected
 * 1--2--3:  1 and 3 are connected through 2
 *
 * This implementation uses concept of a "weight" to avoid too long trees:

DmitrySoshnikov

###
# Explicit delegation-based prototypes implementation.
#
# Implementing JavaScript semantics.
#
# Here we show that "delegation" is just a mechanism (a pattern) for
# implementation of the "inheritance" concept. In this specific case we
# have direct inheritance from objects, skipping the "class" step.
#
# See "OO Relationships" article for some details:

DmitrySoshnikov

/**
 * Destructuring reference bindings.
 * 
 * by Dmitry Soshnikov <[email protected]>
 * MIT Style License
 */

// Bindings of a pattern in destructuring may be not only
// simple variables, but any reference types. In the following
// example we use destructuring assignment to swap two elements

DmitrySoshnikov

%token STRING NULL NUMBER TRUE FALSE

%start JSONText

%%

JSONText : JSONValue;

JSONString : STRING;