/* chapter3/1/pm.h   Author: Wenbo Yang <solrex@gmail.com> <http://solrex.cn>   This file is part of the source code of book "Write Your Own OS with Free   and Open Source Software". Homepage @ <http://share.solrex.cn/WriteOS/>.   This file is licensed under the GNU General Public License; either   version 3 of the License, or (at your option) any later version. *//* Comments below accords to "Chapter 3.4.5: Segment Descriptors" of "Intel   64 and IA-32 Arch. SW Developer's Manual: Volume 3A: System Programming   Guide". *//* GDT Descriptor Attributes     DA_  : Descriptor Attribute     D    : Data Segment     C    : Code Segment     S    : System Segment     R    : Read-only     RW   : Read/Write     A    : Access */.set    DA_32,  0x4000  /* 32-bit segment *//* Descriptor privilege level */.set    DA_DPL0,  0x00  /* DPL = 0 */.set    DA_DPL1,  0x20  /* DPL = 1 */.set    DA_DPL2,  0x40  /* DPL = 2 */.set    DA_DPL3,  0x60  /* DPL = 3 *//* GDT Code- and Data-Segment Types */.set    DA_DR,   0x90   /* Read-Only */.set    DA_DRW,  0x92   /* Read/Write */.set    DA_DRWA, 0x93   /* Read/Write, accessed */.set    DA_C,    0x98   /* Execute-Only */.set    DA_CR,   0x9A   /* Execute/Read */.set    DA_CCO,  0x9C   /* Execute-Only, conforming */.set    DA_CCOR, 0x9E   /* Execute/Read-Only, conforming *//* GDT System-Segment and Gate-Descriptor Types */.set    DA_LDT,      0x82    /* LDT */.set    DA_TaskGate, 0x85    /* Task Gate */.set    DA_386TSS,   0x89    /* 32-bit TSS(Available) */.set    DA_386CGate, 0x8C    /* 32-bit Call Gate */.set    DA_386IGate, 0x8E    /* 32-bit Interrupt Gate */.set    DA_386TGate, 0x8F    /* 32-bit Trap Gate *//* Selector Attributes */.set    SA_RPL0, 0.set    SA_RPL1, 1.set    SA_RPL2, 2.set    SA_RPL3, 3.set    SA_TIG,  0.set    SA_TIL,  4/* MACROS *//* Segment Descriptor data structure.   Usage: Descriptor Base, Limit, Attr    Base:  4byte     Limit: 4byte (low 20 bits available)    Attr:  2byte (lower 4 bits of higher byte are always 0) */.macro Descriptor Base, Limit, Attr    .2byte  \Limit & 0xFFFF    .2byte  \Base & 0xFFFF    .byte   (\Base >> 16) & 0xFF    .2byte  ((\Limit >> 8) & 0xF00) | (\Attr & 0xF0FF)    .byte   (\Base >> 24) & 0xFF.endm/* Gate Descriptor data structure.   Usage: Gate Selector, Offset, PCount, Attr    Selector:  2byte    Offset:    4byte    PCount:    byte    Attr:      byte */.macro Gate  Selector, Offset, PCount, Attr    .2byte     (\Offset & 0xFFFF)    .2byte     \Selector    .2byte     (\PCount & 0x1F) | ((\Attr << 8) & 0xFF00)    .2byte     ((\Offset >> 16) & 0xFFFF).endm