DOCSLIB.ORG

AMD 64-Bit Technology

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Preliminary Information AMD 64-Bit Technology The AMD x86-64™ Architecture Programmers Overview Publication # 24108 Rev: A Issue Date: August 2000 Preliminary Information © 2000 Advanced Micro Devices, Inc. All rights reserved. The contents of this document are provided in connection with Advanced Micro Devices, Inc. (“AMD”) products. AMD makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this publication. Except as set forth in AMD’s Standard Terms and Conditions of Sale, AMD assumes no liability whatsoever, and disclaims any express or implied warranty, relating to its products including, but not limited to, the implied warranty of merchantability, fitness for a particular purpose, or infringement of any intellectual property right. AMD’s products are not designed, intended, authorized or warranted for use as components in systems intended for surgical implant into the body, or in other applications intended to support or sustain life, or in any other applica- tion in which the failure of AMD’s product could create a situation where per- sonal injury, death, or severe property or environmental damage may occur. AMD reserves the right to discontinue or make changes to its products at any time without notice. Trademarks AMD, the AMD logo, x86-64, AMD Athlon, and combinations thereof are trademarks of Advanced Micro Devices, Inc. MMX is a trademark of Intel Corporation. Windows NT is a trademark of Microsoft Corp. Other product names used in this publication are for identification purposes only and may be trademarks of their respective companies. Preliminary Information 24108A—August 2000 AMD 64-Bit Technology Contents Introduction. 1 Motivation for a 64-Bit Architecture . 1 Features of the x86-64™ Architecture . 2 Long Mode . 2 64-Bit Mode . 3 Compatibility Mode . 5 Legacy Mode . 5 Definitions. 6 Notation . 6 Registers. 7 Application Programming . 9 Overview . 9 Application Software Registers and Data Structures . 10 CPUID . 11 Application Registers . 12 General-Purpose Registers (GPRs) . 12 Streaming SIMD Extension (SSE) Registers . 15 Memory Organization . 15 Address Calculations in 64-Bit Mode. 15 FS and GS As Base of Address Calculation . 16 Instruction-Set Conventions . 17 Address-Size and Operand-Size Prefixes. 17 REX Prefixes . 18 REX Prefix Fields . 20 Displacement . 24 Direct Memory-Offset MOVs . 24 Immediates. 24 RIP-Relative Addressing. 24 Default 64-Bit Operand Size . 26 Stack Pointer . 26 Branches . 27 System Programming . 29 Overview . 29 Canonical Address Form . 29 CPUID . 30 System Registers . 31 Extended Feature Enable Register (EFER) . 31 Control Registers. 33 Descriptor Table Registers . 34 Debug Registers. 34 Enabling and Activating Long Mode . 35 Processor Modes . 35 iii Preliminary Information AMD 64-Bit Technology 24108A—August 2000 Activating Long Mode. 36 Virtual-8086 Mode . 39 Compatibility Mode: Support for Legacy Applications . 39 Long-Mode Semantics . 39 Switching Between 64-Bit Mode and Compatibility Mode . 39 Segmentation . 40 Code Segments . 40 Data and Stack Segments . 42 System Descriptors . 44 Virtual Addressing and Paging. 47 Virtual-Address and Physical-Address Size . 47 Paging Data Structures . 47 Enhanced Legacy-Mode Paging . 53 CR2 and CR3 . 54 Address Translation. 55 Privilege-Level Transitions and Far Transfers . 58 Call Gates . 58 SYSCALL and SYSRET . 61 Task State Segments . 63 Interrupts . 65 Gate Descriptor Format . 65 Stack Frame . 67 IRET . 67 Stack Switching . 68 Task Priority . 70 Appendix A Integer Instructions in 64-Bit Mode . 73 General Rules . 73 Operand Size in 64-Bit Mode. 73 Instruction Differences . 93 Invalid Instructions . 93 Single-Byte INC and DEC Instructions . 94 NOP. 94 MOVSXD . 95 Instructions that Reference RSP . 95 Segment-Override Prefixes in 64-Bit Mode. 96 FXSAVE and FXRSTOR . 96 New Encodings for Control and Debug Registers . 97 Appendix B Long Mode Differences . 98 Appendix C Initialization Example . 100 Appendix D Implementation Considerations . 105 Address Size . 105 Operand Alignment . 105 CR8 Interactions with APIC . 106 Physical Address Fields in MSRs . 107 iv Preliminary Information 24108A—August 2000 AMD 64-Bit Technology Introduction AMD 64-bit technology includes the x86-64™ architecture, which is a 64-bit extension of the x86 architecture. The x86-64 architecture supports legacy 16-bit and 32-bit applications and operating systems without modification. It provides recompiled 64-bit applications and operating systems with these new features: I 64-bit flat virtual addressing. I 8 new general-purpose registers (GPRs). I 8 new registers for streaming SIMD extensions (SSE). I 64-bit-wide GPRs and instruction pointer. The x86-64 architecture has a legacy mode in which it supports binary compatibility with existing operating systems and applications, and a new mode in which it supports both the new features for recompiled code as well as binary compatibility with existing applications. The architecture also adds a new instruction-pointer relative-addressing mode, uniform byte- register addressing, and a fast interrupt-prioritizing mechanism. This document describes the new features of AMD’s x86-64 architecture and their differences from legacy x86 architecture. Motivation for a 64-Bit Architecture The need for a 64-bit x86 architecture is driven by applications that address large amounts of virtual and physical memory, such as high-performance servers, database management systems, and CAD tools. These applications benefit from both 64-bit addresses and an increased number of registers. The small number of registers available in the legacy x86 architecture also limits performance in computation-intensive applications such as graphics transform and lighting, circuit simulation, and scientific algorithms. Increasing the number of registers provides a performance boost to many applications. Introduction 1 Preliminary Information AMD 64-Bit Technology 24108A—August 2000 Features of the x86-64™ Architecture The x86-64 architecture extends the legacy x86 architecture by introducing two major features: a 64-bit extension called long mode and register extensions. Long Mode Long mode consists of two sub-modes:.
Recommended publications
  • SYSCALL, IRET ● Opportunistic SYSRET Failed, Do IRET

    SYSCALL, IRET ● Opportunistic SYSRET Failed, Do IRET

    entry_*.S A carefree stroll through kernel entry code Borislav Petkov SUSE Labs [email protected] Reasons for entry into the kernel ● System calls (64-bit, compat, 32-bit) ● Interrupts (NMIs, APIC, timer, IPIs... ) – software: INT 0x0-0xFF, INT3, … – external (hw-generated): CPU-ext logic, async to insn exec ● Architectural exceptions (sync vs async) – faults: precise, reported before faulting insn => restartable (#GP,#PF) – traps: precise, reported after trapping insn (#BP,#DB-both) – aborts: imprecise, not reliably restartable (#MC, unless MCG_STATUS.RIPV) 2 Intr/Ex entry ● IDT, int num index into it (256 vectors); all modes need an IDT ● If handler has a higher CPL, switch stacks ● A picture is always better: 3 45sec guide to Segmentation ● Continuous range at an arbitrary position in VA space ● Segments described by segment descriptors ● … selected by segment selectors ● … by indexing into segment descriptor tables (GDT,LDT,IDT,...) ● … and loaded by the hw into segment registers: – user: CS,DS,{E,F,G}S,SS – system: GDTR,LDTR,IDTR,TR (TSS) 4 A couple more seconds of Segmentation ● L (bit 21) new long mode attr: 1=long mode, 0=compat mode ● D (bit 22): default operand and address sizes ● legacy: D=1b – 32bit, D=0b – 16bit ● long mode: D=0b – 32-bit, L=1,D=1 reserved for future use ● G (bit 23): granularity: G=1b: seg limit scaled by 4K ● DPL: Descriptor Privilege Level of the segment 5 Legacy syscalls ● Call OS through gate descriptor (call, intr, trap or task gate) ● Overhead due to segment-based protection: – load new selector + desc into
  • I386-Engine™ Technical Manual

    I386-Engine™ Technical Manual

    i386-Engine™ C/C++ Programmable, 32-bit Microprocessor Module Based on the Intel386EX Technical Manual 1950 5 th Street, Davis, CA 95616, USA Tel: 530-758-0180 Fax: 530-758-0181 Email: [email protected] http://www.tern.com Internet Email: [email protected] http://www.tern.com COPYRIGHT i386-Engine, VE232, A-Engine, A-Core, C-Engine, V25-Engine, MotionC, BirdBox, PowerDrive, SensorWatch, Pc-Co, LittleDrive, MemCard, ACTF, and NT-Kit are trademarks of TERN, Inc. Intel386EX and Intel386SX are trademarks of Intel Coporation. Borland C/C++ are trademarks of Borland International. Microsoft, MS-DOS, Windows, and Windows 95 are trademarks of Microsoft Corporation. IBM is a trademark of International Business Machines Corporation. Version 2.00 October 28, 2010 No part of this document may be copied or reproduced in any form or by any means without the prior written consent of TERN, Inc. © 1998-2010 1950 5 th Street, Davis, CA 95616, USA Tel: 530-758-0180 Fax: 530-758-0181 Email: [email protected] http://www.tern.com Important Notice TERN is developing complex, high technology integration systems. These systems are integrated with software and hardware that are not 100% defect free. TERN products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices, or systems, or in other critical applications. TERN and the Buyer agree that TERN will not be liable for incidental or consequential damages arising from the use of TERN products. It is the Buyer's responsibility to protect life and property against incidental failure. TERN reserves the right to make changes and improvements to its products without providing notice.
  • Xv6 Booting: Transitioning from 16 to 32 Bit Mode

    Xv6 Booting: Transitioning from 16 to 32 Bit Mode

    238P Operating Systems, Fall 2018 xv6 Boot Recap: Transitioning from 16 bit mode to 32 bit mode 3 November 2018 Aftab Hussain University of California, Irvine BIOS xv6 Boot loader what it does Sets up the hardware. Transfers control to the Boot Loader. BIOS xv6 Boot loader what it does Sets up the hardware. Transfers control to the Boot Loader. how it transfers control to the Boot Loader Boot loader is loaded from the 1st 512-byte sector of the boot disk. This 512-byte sector is known as the boot sector. Boot loader is loaded at 0x7c00. Sets processor’s ip register to 0x7c00. BIOS xv6 Boot loader 2 source source files bootasm.S - 16 and 32 bit assembly code. bootmain.c - C code. BIOS xv6 Boot loader 2 source source files bootasm.S - 16 and 32 bit assembly code. bootmain.c - C code. executing bootasm.S 1. Disable interrupts using cli instruction. (Code). > Done in case BIOS has initialized any of its interrupt handlers while setting up the hardware. Also, BIOS is not running anymore, so better to disable them. > Clear segment registers. Use xor for %ax, and copy it to the rest (Code). 2. Switch from real mode to protected mode. (References: a, b). > Note the difference between processor modes and kernel privilege modes > We do the above switch to increase the size of the memory we can address. BIOS xv6 Boot loader 2 source source file executing bootasm.S m. Let’s 2. Switch from real mode to protected mode. expand on this a little bit Addressing in Real Mode In real mode, the processor sends 20-bit addresses to the memory.
  • X86 Memory Protection and Translation

    X86 Memory Protection and Translation

    2/5/20 COMP 790: OS Implementation COMP 790: OS Implementation Logical Diagram Binary Memory x86 Memory Protection and Threads Formats Allocators Translation User System Calls Kernel Don Porter RCU File System Networking Sync Memory Device CPU Today’s Management Drivers Scheduler Lecture Hardware Interrupts Disk Net Consistency 1 Today’s Lecture: Focus on Hardware ABI 2 1 2 COMP 790: OS Implementation COMP 790: OS Implementation Lecture Goal Undergrad Review • Understand the hardware tools available on a • What is: modern x86 processor for manipulating and – Virtual memory? protecting memory – Segmentation? • Lab 2: You will program this hardware – Paging? • Apologies: Material can be a bit dry, but important – Plus, slides will be good reference • But, cool tech tricks: – How does thread-local storage (TLS) work? – An actual (and tough) Microsoft interview question 3 4 3 4 COMP 790: OS Implementation COMP 790: OS Implementation Memory Mapping Two System Goals 1) Provide an abstraction of contiguous, isolated virtual Process 1 Process 2 memory to a program Virtual Memory Virtual Memory 2) Prevent illegal operations // Program expects (*x) – Prevent access to other application or OS memory 0x1000 Only one physical 0x1000 address 0x1000!! // to always be at – Detect failures early (e.g., segfault on address 0) // address 0x1000 – More recently, prevent exploits that try to execute int *x = 0x1000; program data 0x1000 Physical Memory 5 6 5 6 1 2/5/20 COMP 790: OS Implementation COMP 790: OS Implementation Outline x86 Processor Modes • x86
  • Virtual Memory in X86

    Virtual Memory in X86

    Fall 2017 :: CSE 306 Virtual Memory in x86 Nima Honarmand Fall 2017 :: CSE 306 x86 Processor Modes • Real mode – walks and talks like a really old x86 chip • State at boot • 20-bit address space, direct physical memory access • 1 MB of usable memory • No paging • No user mode; processor has only one protection level • Protected mode – Standard 32-bit x86 mode • Combination of segmentation and paging • Privilege levels (separate user and kernel) • 32-bit virtual address • 32-bit physical address • 36-bit if Physical Address Extension (PAE) feature enabled Fall 2017 :: CSE 306 x86 Processor Modes • Long mode – 64-bit mode (aka amd64, x86_64, etc.) • Very similar to 32-bit mode (protected mode), but bigger address space • 48-bit virtual address space • 52-bit physical address space • Restricted segmentation use • Even more obscure modes we won’t discuss today xv6 uses protected mode w/o PAE (i.e., 32-bit virtual and physical addresses) Fall 2017 :: CSE 306 Virt. & Phys. Addr. Spaces in x86 Processor • Both RAM hand hardware devices (disk, Core NIC, etc.) connected to system bus • Mapped to different parts of the physical Virtual Addr address space by the BIOS MMU Data • You can talk to a device by performing Physical Addr read/write operations on its physical addresses Cache • Devices are free to interpret reads/writes in any way they want (driver knows) System Interconnect (Bus) : all addrs virtual DRAM Network … Disk (Memory) Card : all addrs physical Fall 2017 :: CSE 306 Virt-to-Phys Translation in x86 0xdeadbeef Segmentation 0x0eadbeef Paging 0x6eadbeef Virtual Address Linear Address Physical Address Protected/Long mode only • Segmentation cannot be disabled! • But can be made a no-op (a.k.a.
  • Protected Mode - Wikipedia

    Protected Mode - Wikipedia

    2/12/2019 Protected mode - Wikipedia Protected mode In computing, protected mode, also called protected virtual address mode,[1] is an operational mode of x86- compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.[2][3] When a processor that supports x86 protected mode is powered on, it begins executing instructions in real mode, in order to maintain backward compatibility with earlier x86 processors.[4] Protected mode may only be entered after the system software sets up one descriptor table and enables the Protection Enable (PE) bit in the control register 0 (CR0).[5] Protected mode was first added to the x86 architecture in 1982,[6] with the release of Intel's 80286 (286) processor, and later extended with the release of the 80386 (386) in 1985.[7] Due to the enhancements added by protected mode, it has become widely adopted and has become the foundation for all subsequent enhancements to the x86 architecture,[8] although many of those enhancements, such as added instructions and new registers, also brought benefits to the real mode. Contents History The 286 The 386 386 additions to protected mode Entering and exiting protected mode Features Privilege levels Real mode application compatibility Virtual 8086 mode Segment addressing Protected mode 286 386 Structure of segment descriptor entry Paging Multitasking Operating systems See also References External links History https://en.wikipedia.org/wiki/Protected_mode
  • Chapter 2 Powerpc Register Set

    Chapter 2 Powerpc Register Set

    Chapter 2 PowerPC Register Set 20 20 This chapter describes the register organization defined by the three levels of the PowerPC U architecture—user instruction set architecture (UISA), virtual environment architecture V (VEA), and operating environment architecture (OEA). The PowerPC architecture defines O register-to-register operations for all computational instructions. Source data for these instructions are accessed from the on-chip registers or are provided as immediate values embedded in the opcode. The three-register instruction format allows specification of a target register distinct from the two source registers, thus preserving the original data for use by other instructions and reducing the number of instructions required for certain operations. Data is transferred between memory and registers with explicit load and store instructions only. Note that the handling of reserved bits in any register is implementation-dependent. Software is permitted to write any value to a reserved bit in a register. However, a subsequent reading of the reserved bit returns 0 if the value last written to the bit was 0 and returns an undefined value (may be 0 or 1) otherwise. This means that even if the last value written to a reserved bit was 1, reading that bit may return 0. 2.1 PowerPC UISA Register Set The PowerPC UISA registers, shown in Figure 2-1, can be accessed by either user- or U supervisor-level instructions (the architecture specification refers to user-level and supervisor-level as problem state and privileged state respectively). The general-purpose registers (GPRs) and floating-point registers (FPRs) are accessed as instruction operands.
  • A Comparison of Protection Lookaside Buffers and the PA-RISC

    A Comparison of Protection Lookaside Buffers and the PA-RISC

    rI3 HEWLETT ~~PACKARD A Comparison ofProtection Lookaside Buffers and the PA·RISC Protection Architecture John Wilkes, Bart Sears Computer Systems Laboratory HPL-92-55 March 1992 processor architecture, Eric Koldinger and others at the University of single address space, 64­ Washington Department of Computer Science have bitaddressing, protection, proposed a new model for memory protection in PA-RISe, protection single-address-space architectures. This paper lookaside buffers, PLB, compares the Washington proposal with what translation lookaside already exists in PA-RISC, and suggests some buffers,TLB, cache incremental improvements to the latter that would indexing, virtually­ provide most of the benefits of the former. addressed caches Internal Accession Date Only © Copyright Hewlett-Packard Company 1992 1 Introduction A recent technical report by Eric Koldinger and others [Koldinger91] proposes a new model for managing protectioninformationinsingle address space processors. This paper is one outcome of discussions withthe authors about the real differences betweentheir proposal and the scheme usedinPA-RISC[Lee89,HPPA90]:it offers a restatement of the newproposal, a comparisonwith the existing PA-RISCarchitecture, and some thoughts onhow the PA-RISCarchitecture mightbe extended in the future to provide some of the benefits that the PLBidea was trying to achieve. The reader is assumed to be familiar withmodem TLB,cache and processor architectures; with luck, sufficient information is provided in this paper that detailed prior knowledge about either the Washington proposal or PA-RISCisn't required. Example To help illustrate some of the finer points of the different protectionmodels, anexample based on the LRPC work of Brian Bershad is used [Bershad90] (see Figure 1).
  • Intel® 64 and IA-32 Architectures Software Developer's Manual

    Intel® 64 and IA-32 Architectures Software Developer's Manual

    Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3B: System Programming Guide, Part 2 NOTE: The Intel® 64 and IA-32 Architectures Software Developer's Manual consists of five volumes: Basic Architecture, Order Number 253665; Instruction Set Reference A-M, Order Number 253666; Instruction Set Reference N-Z, Order Number 253667; System Programming Guide, Part 1, Order Number 253668; System Programming Guide, Part 2, Order Number 253669. Refer to all five volumes when evaluating your design needs. Order Number: 253669-029US November 2008 INFORMATION IN THIS DOCUMENT IS PROVIDED IN CONNECTION WITH INTEL PRODUCTS. NO LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANT- ED BY THIS DOCUMENT. EXCEPT AS PROVIDED IN INTEL'S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, INTEL ASSUMES NO LIABILITY WHATSOEVER AND INTEL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY, RELATING TO SALE AND/OR USE OF INTEL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. UNLESS OTHERWISE AGREED IN WRITING BY INTEL, THE INTEL PRODUCTS ARE NOT DESIGNED NOR IN- TENDED FOR ANY APPLICATION IN WHICH THE FAILURE OF THE INTEL PRODUCT COULD CREATE A SITUA- TION WHERE PERSONAL INJURY OR DEATH MAY OCCUR. Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of any features or instructions marked "reserved" or "unde- fined." Intel reserves these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them.
  • The Evolution of an X86 Virtual Machine Monitor

    The Evolution of an X86 Virtual Machine Monitor

    The Evolution of an x86 Virtual Machine Monitor Ole Agesen, Alex Garthwaite, Jeffrey Sheldon, Pratap Subrahmanyam {agesen, alextg, jeffshel, pratap}@vmware.com ABSTRACT While trap-and-emulate virtualization on mainframes was Twelve years have passed since VMware engineers first virtu- well understood at the time, it was – unsurprisingly – not a alized the x86 architecture. This technological breakthrough design goal for the 4004, whose first application was in fact kicked off a transformation of an entire industry, and virtu- a Busicom calculator [7]. However, as x86 CPUs expanded alization is now (once again) a thriving business with a wide their reach, the case for virtualization gradually emerged. range of solutions being deployed, developed and proposed. There was just one problem, seemingly fundamental: the But at the base of it all, the fundamental quest is still the generally accepted wisdom held that x86 virtualization was same: running virtual machines as well as we possibly can impossible, or at best merely impractical, due to inherited on top of a virtual machine monitor. architectural quirks and a requirement to retain compatibil- ity with legacy code. We review how the x86 architecture was originally virtual- ized in the days of the Pentium II (1998), and follow the This impasse was broken twelve years ago when VMware evolution of the virtual machine monitor forward through engineers first virtualized the x86 architecture entirely in the introduction of virtual SMP, 64 bit (x64), and hard- software. By basing the virtual machine monitor (VMM) ware support for virtualization to finish with a contempo- on binary translation, the architectural features that pre- rary challenge, nested virtualization.
  • Chapter 3 Protected-Mode Memory Management

    Chapter 3 Protected-Mode Memory Management

    CHAPTER 3 PROTECTED-MODE MEMORY MANAGEMENT This chapter describes the Intel 64 and IA-32 architecture’s protected-mode memory management facilities, including the physical memory requirements, segmentation mechanism, and paging mechanism. See also: Chapter 5, “Protection” (for a description of the processor’s protection mechanism) and Chapter 20, “8086 Emulation” (for a description of memory addressing protection in real-address and virtual-8086 modes). 3.1 MEMORY MANAGEMENT OVERVIEW The memory management facilities of the IA-32 architecture are divided into two parts: segmentation and paging. Segmentation provides a mechanism of isolating individual code, data, and stack modules so that multiple programs (or tasks) can run on the same processor without interfering with one another. Paging provides a mech- anism for implementing a conventional demand-paged, virtual-memory system where sections of a program’s execution environment are mapped into physical memory as needed. Paging can also be used to provide isolation between multiple tasks. When operating in protected mode, some form of segmentation must be used. There is no mode bit to disable segmentation. The use of paging, however, is optional. These two mechanisms (segmentation and paging) can be configured to support simple single-program (or single- task) systems, multitasking systems, or multiple-processor systems that used shared memory. As shown in Figure 3-1, segmentation provides a mechanism for dividing the processor’s addressable memory space (called the linear address space) into smaller protected address spaces called segments. Segments can be used to hold the code, data, and stack for a program or to hold system data structures (such as a TSS or LDT).
  • X86 Memory Protection and Translation

    X86 Memory Protection and Translation

    x86 Memory Protection and Translation Don Porter CSE 506 Lecture Goal ò Understand the hardware tools available on a modern x86 processor for manipulating and protecting memory ò Lab 2: You will program this hardware ò Apologies: Material can be a bit dry, but important ò Plus, slides will be good reference ò But, cool tech tricks: ò How does thread-local storage (TLS) work? ò An actual (and tough) Microsoft interview question Undergrad Review ò What is: ò Virtual memory? ò Segmentation? ò Paging? Two System Goals 1) Provide an abstraction of contiguous, isolated virtual memory to a program 2) Prevent illegal operations ò Prevent access to other application or OS memory ò Detect failures early (e.g., segfault on address 0) ò More recently, prevent exploits that try to execute program data Outline ò x86 processor modes ò x86 segmentation ò x86 page tables ò Software vs. Hardware mechanisms ò Advanced Features ò Interesting applications/problems x86 Processor Modes ò Real mode – walks and talks like a really old x86 chip ò State at boot ò 20-bit address space, direct physical memory access ò Segmentation available (no paging) ò Protected mode – Standard 32-bit x86 mode ò Segmentation and paging ò Privilege levels (separate user and kernel) x86 Processor Modes ò Long mode – 64-bit mode (aka amd64, x86_64, etc.) ò Very similar to 32-bit mode (protected mode), but bigger ò Restrict segmentation use ò Garbage collect deprecated instructions ò Chips can still run in protected mode with old instructions Translation Overview 0xdeadbeef Segmentation 0x0eadbeef Paging 0x6eadbeef Virtual Address Linear Address Physical Address Protected/Long mode only ò Segmentation cannot be disabled! ò But can be a no-op (aka flat mode) x86 Segmentation ò A segment has: ò Base address (linear address) ò Length ò Type (code, data, etc).