Labels:text | screenshot | font | number | document OCR: Figure 1 Common Intel x86 Registers FAX Multipurpose, Return values from a function are usually stored. in' FAX. Low.16 bits are referenced as AX. AX can be further subdivided into AL (the low 8 bits); and All (the upper'8 bits of AX), EBX Multipurpose: [ ow 16 bits are referenced'as BX, BX can be further subdivided into BL (the low 8 hits), and BHadthe upper 8'bits of BX) ECX Multipurpose. Often used as a counter, for example, to hold the number of loop iterations that should be performed. Low 16 bits are referenced as CX, CX can be further sulidivided jnto CL (the low 8 bits), abil CH (the upper 8 bits of CX). EDX Multipurpose. Low 16 bits are referenced us DX. DX can be further subdivided into DL the low 8 bits), and DH (the upper 8 bits of DX). ESI Multipurpose:In certain operations that move or compare memory; ESI contains the source address. Low 16 bits are referenced.as SI EDI Multipurpose, In certain operations that move or compare memory, ED) contains the destination address. Low. 15 bits aire referencedres DI: ESP Stack pointer : Implicitly changed by PUSH. POP, CALL; and RET instructions EBP Base pointer. Usually points to the current stack frame for a procedure, Procedure parameter's are usually at positive offset's from EBP (for example, EBP +8) Local variables are usdally'at negative offiets ( for example. EBP-16). Sometimes, optimizing compilers won't use a stack frame, and use EBP aa a multipurpose register: EFLAGS Rarely directly referenced. Instead, instructions implicitly set or clear bitfields within the EFLAGS register to represent. a certain state. For example, when the result of a mathematical operation is zero; the Zero flag is toggled on in the EFLAGS register. The conditional jump instructions make use of the EFLAGS register. 16.Int. Under Wings; the FS register points to a data structure with information pertaining to the current threadi ES is a segment register ( segment registers are beyond the scope of this discus tion ): Intel CPU's have sik, segment, registers, but the operating systemh sels them up and maintains them. Win32 compilers only need to explicitly refer to the FS segment refaster, which is used for things like structured exception handling and thread local storage.
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