Intel base instruction -- bnd

       In decompile x86 64 position pstree They found f2 e9 e1 ff ff ff        bnd jmpq 2020 , See you for the first time bnd This Directive , check intel manual , Only BNDCL、BNDMK Wait for the explanation of the instruction , No, bnd Any description of , Have to resort to the Internet . I really see the instructions about this instruction , It is Intel MPX Part of .

 

       What is? MPX？

       Memory Protection Extensions, Memory protection extension .

       BND yes Intel MPX Part of , Indicates the return target （ Or usually branch target , because BND It can be applied to any control flow instruction ） According to BND0 To BND3 Check the boundary specified in the register , Otherwise, an exception will be generated —— Indicates a potential stack overflow 、 Programming errors or malicious code attacks .

       No support for Intel MPX On the processor , Or when MPX When disabled ,BND The prefix appears as no operation , Therefore, there is no need to compile two versions of code （ With a BND Prefix , One without BND Prefix ）.

       Be careful BND Prefix encoding and REPNE The prefix code is the same （ All are F2）, So I don't know MPX The old disassembler of may display this instruction sequence as REPNE RET（ or REPNE JMP, REPNE CALL etc. ）. This usage is similar to REP RET idiom irrelevant , The latter assumes that the prefix has no operational behavior , Purely for solving old problems CPU Performance issues on .