Operand sizes from within a program when operating in

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Unformatted text preview: f effective address calculations is 64 bits. An effective-address calculation uses a 64-bit base and index registers and sign-extend displacements to 64 bits. In the flat address space of 64-bit mode, linear addresses are equal to effective addresses because the base address is zero. In the event that FS or GS segments are used with a non-zero base, this rule does not hold. In 64-bit mode, the effective address components are added and the effective address is truncated (See for example the instruction LEA) before adding the full 64-bit segment base. The base is never truncated, regardless of addressing mode in 64-bit mode. The instruction pointer is extended to 64 bits to support 64-bit code offsets. The 64-bit instruction pointer is called the RIP. Table 3-1 shows the relationship between RIP, EIP, and IP. Table 3-1. Instruction Pointer Sizes Bits 63:32 16-bit instruction pointer 32-bit instruction pointer 64-bit instruction pointer Not Modified Zero Extension RIP EIP Bits 31:16 Bits 15:0 IP Generally, displacements and immediates in 64-bit mode are not extended to 64 bits. They are still limited to 32 bits and sign-extended during effective-address calculations. In 64-bit mode, however, support is provided for 64-bit displacement and immediate forms of the MOV instruction. All 16-bit and 32-bit address calculations are zero-extended in IA-32e mode to form 64-bit addresses. Address calculations are first truncated to the effective address 3-12 Vol. 1 BASIC EXECUTION ENVIRONMENT size of the current mode (64-bit mode or compatibility mode), as overridden by any address-size prefix. The result is then zero-extended to the full 64-bit address width. Because of this, 16-bit and 32-bit applications running in compatibility mode can access only the low 4 GBytes of the 64-bit mode effective addresses. Likewise, a 32-bit address generated in 64-bit mode can access only the low 4 GBytes of the 64-bit mode effective addresses. Canonical Addressing In 64-bit mode, an address is considered to be in canonical form if address bits 63 through to the most-significant implemented bit by the microarchitecture are set to either all ones or all zeros. Intel 64 architecture defines a 64-bit linear address. Implementations can support less. The first implementation of IA-32 processors with Intel 64 architecture supports a 48-bit linear address. This means a canonical address must have bits 63 through 48 set to zeros or ones (depending on whether bit 47 is a zero or one). Although implementations may not use all 64 bits of the linear address, they should check bits 63 through the most-significant implemented bit to see if the address is in canonical form. If a linear-memory reference is not in canonical form, the implementation should generate an exception. In most cases, a general-protection exception (#GP) is generated. However, in the case of explicit or implied stack references, a stack fault (#SS) is generated. Instructions that have implied stack referenc...
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This note was uploaded on 10/01/2013 for the course CPE 103 taught by Professor Watlins during the Winter '11 term at Mississippi State.

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