libVEX学习

VEX IR是一种更加接近于compiler使用的中间语言/中间表示，它是不依赖于特定体系架构的。

1. Code Blocks

code blocks是VEX处理代码的一个单元，使用IRSB结构体表示：

/* Code blocks, which in proper compiler terminology are superblocks
   (single entry, multiple exit code sequences) contain:
　　【与Intel Pin中的概念trace是相似的】

   - A table giving a type for each temp (the "type environment")
   - An expandable array of statements
   - An expression of type 32 or 64 bits, depending on the
     guest's word size, indicating the next destination if the block 
     executes all the way to the end, without a side exit
   - An indication of any special actions (JumpKind) needed
     for this final jump.
   
   "IRSB" stands for "IR Super Block".
*/
typedef
   struct {
      IRTypeEnv* tyenv;
      IRStmt**   stmts;
      Int        stmts_size;
      Int        stmts_used;
      IRExpr*    next;
      IRJumpKind jumpkind;
   }
   IRSB;

　　

 Each IRSB contains three things:
   - a type environment, which indicates the type of each temporary
     value present in the IRSB
   - a list of statements, which represent code
   - a jump that exits from the end the IRSB

　

2. Statements and Expressions

Statements (type 'IRStmt') represent operations with side-effects,
   eg.  guest register writes, stores, and assignments to temporaries.
   Expressions (type 'IRExpr') represent operations without
   side-effects, eg. arithmetic operations, loads, constants.
   Expressions can contain sub-expressions, forming expression trees,
   eg. (3 + (4 * load(addr1)).

Statements： IRStmt

代表着有side-effect的操作；

Expressions: IRExpr

代表着没有side-effect的操作；

3. Storage of guest state

guest state，其实就是代表目标机器寄存器的一片连续的缓存。

在这片缓存上可以进行Put/Get操作。

Put/Get操作需要提供两个参数：

在代表guest state的缓存中的offset

代表操作数长度的type