Canonical Addressing

最新推荐文章于 2023-06-07 20:34:58 发布

原创最新推荐文章于 2023-06-07 20:34:58 发布 · 1.9k 阅读

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#exception #reference #include

本文探讨了在64位模式中规范地址的概念及其实现细节。在Intel64架构下，规范地址要求地址的最高位未实现的部分要么全部为0要么全部为1。文章还介绍了当地址不处于规范形式时处理器如何触发异常的情况。

3.3.7.1 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 references, by default, use the SS segment register. These include PUSH/POP-related instructions and instructions using RSP/RBP as base registers. In these cases, the canonical fault is #SF.

If an instruction uses base registers RSP/RBP and uses a segment override prefix to specify a non-SS segment, a canonical fault generates a #GP (instead of an #SF). In 64-bit mode, only FS and GS segment-overrides are applicable in this situation. Other segment override prefixes (CS, DS, ES and SS) are ignored. Note that this also means that an SS segment-override applied to a “non-stack” register reference is ignored. Such a sequence still produces a #GP for a canonical fault (and not an #SF).