绋嬪簭6-3 linux/boot/head.s

  1 /*

  2  *  linux/boot/head.s

  3  *

  4  *  (C) 1991  Linus Torvalds

  5  */

  6

  7 /*

  8  *  head.s contains the 32-bit startup code.

  9  *

 10  * NOTE!!! Startup happens at absolute address 0x00000000, which is also where

 11  * the page directory will exist. The startup code will be overwritten by

 12  * the page directory.

 13  */

    /*

     *  head.s鍚�鏈�32浣嶅惎鍔ㄤ唬鐮併��

     * 娉ㄦ剰!!! 32浣嶅惎鍔ㄤ唬鐮佹槸浠庣粷瀵瑰湴鍧�0x00000000寮�濮嬬殑锛岃繖閲屼篃鍚屾牱鏄�椤电洰褰曞皢瀛樺湪鐨勫湴鏂癸��

     * 鍥犳�よ繖閲岀殑鍚�鍔ㄤ唬鐮佸皢琚�椤电洰褰曡�嗙洊鎺夈��

     */

 14 .text

 15 .globl _idt,_gdt,_pg_dir,_tmp_floppy_area

 16 _pg_dir:                   # 椤电洰褰曞皢浼氬瓨鏀惧湪杩欓噷銆�

 

    # 鍐嶆�℃敞鎰�!!! 杩欓噷宸茬粡澶勪簬32浣嶈繍琛屾ā寮忥紝鍥犳�よ繖閲岀��$0x10骞朵笉鏄�鎶婂湴鍧�0x10瑁呭叆鍚勪釜

    # 娈靛瘎瀛樺櫒锛屽畠鐜板湪鍏跺疄鏄�鍏ㄥ眬娈垫弿杩扮�﹁〃涓�鐨勫亸绉诲�硷紝鎴栬�呮洿鍑嗙‘鍦拌�存槸涓�涓�鎻忚堪绗﹁〃椤�

    # 鐨勯�夋嫨绗︺�傛湁鍏抽�夋嫨绗︾殑璇存槑璇峰弬瑙�setup.s涓�193琛屼笅鐨勮�存槑銆傝繖閲�$0x10鐨勫惈涔夋槸璇锋眰

    # 鐗规潈绾�0(浣�0-1=0)銆侀�夋嫨鍏ㄥ眬鎻忚堪绗﹁〃(浣�2=0)銆侀�夋嫨琛ㄤ腑绗�2椤�(浣�3-15=2)銆傚畠姝ｅソ鎸�

    # 鍚戣〃涓�鐨勬暟鎹�娈垫弿杩扮�﹂」銆傦紙鎻忚堪绗︾殑鍏蜂綋鏁板�煎弬瑙佸墠闈�setup.s涓�212锛�213琛岋級

    # 涓嬮潰浠ｇ爜鐨勫惈涔夋槸锛氳�剧��ds,es,fs,gs涓�setup.s 涓�鏋勯�犵殑鏁版嵁娈碉紙鍏ㄥ眬娈垫弿杩扮�﹁〃绗�2椤癸級

    # 鐨勯�夋嫨绗�=0x10锛屽苟灏嗗爢鏍堟斁缃�鍦�stack_start鎸囧悜鐨�user_stack鏁扮粍鍖猴紝鐒跺悗浣跨敤鏈�绋嬪��

    # 鍚庨潰瀹氫箟鐨勬柊涓�鏂�鎻忚堪绗﹁〃鍜屽叏灞�娈垫弿杩拌〃銆傛柊鍏ㄥ眬娈垫弿杩拌〃涓�鍒濆�嬪唴瀹逛笌setup.s涓�鐨勫熀鏈�

    # 涓�鏍凤紝浠呮�甸檺闀夸��8MB淇�鏀规垚浜�16MB銆�stack_start瀹氫箟鍦�kernel/sched.c锛�69琛屻�傚畠鏄�鎸囧��

    # user_stack鏁扮粍鏈�绔�鐨勪竴涓�闀挎寚閽堛�傜��23琛岃�剧疆杩欓噷浣跨敤鐨勬爤锛屽�戜笖绉颁负绯荤粺鏍堛�備絾鍦ㄧЩ鍔ㄥ埌

    # 浠诲姟0鎵ц�岋��init/main.c涓�137琛岋級浠ュ悗璇ユ爤灏辫��鐢ㄤ綔浠诲姟0鍜屼换鍔�1鍏卞悓浣跨敤鐨勭敤鎴锋爤浜嗐��

 

 17 startup_32:                  # 18-22琛岃�剧疆鍚勪釜鏁版嵁娈靛瘎瀛樺櫒銆�

 18         movl $0x10,%eax      # 瀵逛簬GNU姹囩紪锛屾瘡涓�鐩存帴鎿嶄綔鏁拌�佷互'$'寮�濮嬶紝鍚﹀垯琛ㄧず鍦板潃銆�

                                 # 姣忎釜瀵勫瓨鍣ㄥ悕閮借�佷��'%'寮�澶达紝eax琛ㄧず鏄�32浣嶇殑ax瀵勫瓨鍣ㄣ��

 19         mov %ax,%ds

 20         mov %ax,%es

 21         mov %ax,%fs

 22         mov %ax,%gs

 23         lss _stack_start,%esp      # 琛ㄧず_stack_start猫ss:esp锛岃�剧疆绯荤粺鍫嗘爤銆�

                                       # stack_start瀹氫箟鍦�kernel/sched.c锛�69琛屻��

 24         call setup_idt             # 璋冪敤璁剧疆涓�鏂�鎻忚堪绗﹁〃瀛愮▼搴忋��

 25         call setup_gdt             # 璋冪敤璁剧疆鍏ㄥ眬鎻忚堪绗﹁〃瀛愮▼搴忋��

 26         movl $0x10,%eax            # reload all the segment registers

 27         mov %ax,%ds                # after changing gdt. CS was already

 28         mov %ax,%es                # reloaded in 'setup_gdt'

 29         mov %ax,%fs                # 鍥犱负淇�鏀逛��gdt锛屾墍浠ラ渶瑕侀噸鏂拌�呰浇鎵�鏈夌殑娈靛瘎瀛樺櫒銆�

 30         mov %ax,%gs                # CS浠ｇ爜娈靛瘎瀛樺櫒宸茬粡鍦�setup_gdt涓�閲嶆柊鍔犺浇杩囦簡銆�

 

    # 鐢变簬娈垫弿杩扮�︿腑鐨勬�甸檺闀夸粠setup.s涓�鐨�8MB鏀规垚浜嗘湰绋嬪簭璁剧疆鐨�16MB锛堣��setup.s琛�208-216

    # 鍜屾湰绋嬪簭鍚庨潰鐨�235-236琛岋級锛屽洜姝よ繖閲屽啀娆″�规墍鏈夋�靛瘎瀛樺櫒鎵ц�屽姞杞芥搷浣滄槸蹇呴』鐨勩�傚彟澶栵紝閫氳繃

    # 浣跨敤bochs璺熻釜瑙傚療锛屽�傛灉涓嶅��CS鍐嶆�℃墽琛屽姞杞斤紝閭ｄ箞鍦ㄦ墽琛屽��26琛屾椂CS浠ｇ爜娈典笉鍙�瑙侀儴鍒嗕��

    # 鐨勯檺闀胯繕鏄�8MB銆傝繖鏍风湅鏉ュ簲璇ラ噸鏂板姞杞�CS銆備絾鏄�鐢变��setup.s涓�鐨勫唴鏍镐唬鐮佹�垫弿杩扮�︿笌鏈�绋嬪簭涓�

    # 閲嶆柊璁剧疆鐨勪唬鐮佹�垫弿杩扮�﹂櫎浜嗘�甸檺闀夸互澶栧叾浣欓儴鍒嗗畬鍏ㄤ竴鏍凤紝8MB鐨勯檺闀垮湪鍐呮牳鍒濆�嬪寲闃舵�典笉浼氭湁

    # 闂�棰橈紝鑰屼笖鍦ㄤ互鍚庡唴鏍告墽琛岃繃绋嬩腑娈甸棿璺宠浆鏃朵細閲嶆柊鍔犺浇CS銆傚洜姝よ繖閲屾病鏈夊姞杞藉畠骞舵病鏈夎�╃▼搴�

    # 鍑洪敊銆�

    # 閽堝�硅�ラ棶棰橈紝鐩�鍓嶅唴鏍镐腑灏卞湪绗�25琛屼箣鍚庢坊鍔犱簡涓�鏉￠暱璺宠浆鎸囦护锛�'ljmp $(__KERNEL_CS),$1f'锛�

    # 璺宠浆鍒扮��26琛屾潵纭�淇�CS纭�瀹炲張琚�閲嶆柊鍔犺浇銆�

 

 31         lss _stack_start,%esp

 

    # 32-36琛岀敤浜庢祴璇�A20鍦板潃绾挎槸鍚﹀凡缁忓紑鍚�銆傞噰鐢ㄧ殑鏂规硶鏄�鍚戝唴瀛樺湴鍧�0x000000澶勫啓鍏ヤ换鎰�

    # 涓�涓�鏁板�硷紝鐒跺悗鐪嬪唴瀛樺湴鍧�0x100000(1M)澶勬槸鍚︿篃鏄�杩欎釜鏁板�笺�傚�傛灉涓�鐩寸浉鍚岀殑璇濓紝灏变竴鐩�

    # 姣旇緝涓嬪幓锛屼篃鍗虫�诲惊鐜�銆佹�绘満銆傝〃绀哄湴鍧�A20绾挎病鏈夐�夐�氾紝缁撴灉鍐呮牳灏变笉鑳戒娇鐢�1MB浠ヤ笂鍐呭瓨銆�

    #

    # 33琛屼笂鐨�'1:'鏄�涓�涓�灞�閮ㄧ�﹀彿鏋勬垚鐨勬爣鍙枫�傛爣鍙风敱绗﹀彿鍚庤窡涓�涓�鍐掑彿缁勬垚銆傛�ゆ椂璇ョ�﹀彿琛ㄧず娲诲姩

    # 浣嶇疆璁℃暟锛�Active location counter锛夌殑褰撳墠鍊硷紝骞跺彲浠ヤ綔涓烘寚浠ょ殑鎿嶄綔鏁般�傚眬閮ㄧ�﹀彿鐢ㄤ簬甯�鍔�

    # 缂栬瘧鍣ㄥ拰缂栫▼浜哄憳涓存椂浣跨敤涓�浜涘悕绉般�傚叡鏈�10涓�灞�閮ㄧ�﹀彿鍚嶏紝鍙�鍦ㄦ暣涓�绋嬪簭涓�閲嶅�嶄娇鐢ㄣ�傝繖浜涚�﹀��

    # 鍚嶄娇鐢ㄥ悕绉�'0'銆�'1'銆�...銆�'9'鏉ュ紩鐢ㄣ�備负浜嗗畾涔変竴涓�灞�閮ㄧ�﹀彿锛岄渶鎶婃爣鍙峰啓鎴�'N:'褰㈠紡锛堝叾涓�N

    # 琛ㄧず涓�涓�鏁板瓧锛夈�備负浜嗗紩鐢ㄥ厛鍓嶆渶杩戝畾涔夌殑杩欎釜绗﹀彿锛岄渶瑕佸啓鎴�'Nb'锛屽叾涓�N鏄�瀹氫箟鏍囧彿鏃朵娇鐢ㄧ��

    # 鏁板瓧銆備负浜嗗紩鐢ㄤ竴涓�灞�閮ㄦ爣鍙风殑涓嬩竴涓�瀹氫箟锛岄渶瑕佸啓鎴�'Nf'锛岃繖閲�N鏄�10涓�鍓嶅悜寮曠敤涔嬩竴銆備笂闈�

    # 'b'琛ㄧず鈥�鍚戝悗锛�backwards锛�鈥�锛�'f'琛ㄧず鈥�鍚戝墠锛�forwards锛�鈥�銆傚湪姹囩紪绋嬪簭鐨勬煇涓�澶勶紝鎴戜滑鏈�澶�

    # 鍙�浠ュ悜鍚�/鍚戝墠寮曠敤10涓�鏍囧彿锛堟渶杩滅��10涓�锛夈��

 

 32         xorl %eax,%eax

 33 1:      incl %eax                  # check that A20 really IS enabled

 34         movl %eax,0x000000         # loop forever if it isn't

 35         cmpl %eax,0x100000

 36         je 1b                      # '1b'琛ㄧず鍚戝悗(backward)璺宠浆鍒版爣鍙�1鍘伙紙33琛岋級銆�

                                       # 鑻ユ槸'5f'鍒欒〃绀哄悜鍓�(forward)璺宠浆鍒版爣鍙�5鍘汇��

 37 /*

 38  * NOTE! 486 should set bit 16, to check for write-protect in supervisor

 39  * mode. Then it would be unnecessary with the "verify_area()"-calls.

 40  * 486 users probably want to set the NE (#5) bit also, so as to use

 41  * int 16 for math errors.

 42  */

    /*

     * 娉ㄦ剰! 鍦ㄤ笅闈㈣繖娈电▼搴忎腑锛�486搴旇�ュ皢浣�16缃�浣嶏紝浠ユ��鏌ュ湪瓒呯骇鐢ㄦ埛妯″紡涓嬬殑鍐欎繚鎶�,

     * 姝ゅ悗 "verify_area()" 璋冪敤灏变笉闇�瑕佷簡銆�486鐨勭敤鎴烽�氬父涔熶細鎯冲皢NE(#5)缃�浣嶏紝浠ヤ��

     * 瀵规暟瀛﹀崗澶勭悊鍣ㄧ殑鍑洪敊浣跨敤int 16銆�

     */

    # 涓婇潰鍘熸敞閲婁腑鎻愬埌鐨�486 CPU涓�CR0鎺у埗瀵勫瓨鍣ㄧ殑浣�16鏄�鍐欎繚鎶ゆ爣蹇�WP锛�Write-Protect锛夛紝

    # 鐢ㄤ簬绂佹�㈣秴绾х敤鎴风骇鐨勭▼搴忓悜涓�鑸�鐢ㄦ埛鍙�璇婚〉闈�涓�杩涜�屽啓鎿嶄綔銆傝�ユ爣蹇椾富瑕佺敤浜庢搷浣滅郴缁熷湪鍒涘��

    # 鏂拌繘绋嬫椂瀹炵幇鍐欐椂澶嶅埗锛�copy-on-write锛夋柟娉曘��

    # 涓嬮潰杩欐�电▼搴忥��43-65锛夌敤浜庢��鏌ユ暟瀛﹀崗澶勭悊鍣ㄨ姱鐗囨槸鍚﹀瓨鍦ㄣ�傛柟娉曟槸淇�鏀规帶鍒跺瘎瀛樺��CR0锛屽湪

    # 鍋囪�惧瓨鍦ㄥ崗澶勭悊鍣ㄧ殑鎯呭喌涓嬫墽琛屼竴涓�鍗忓�勭悊鍣ㄦ寚浠わ紝濡傛灉鍑洪敊鐨勮瘽鍒欒�存槑鍗忓�勭悊鍣ㄨ姱鐗囦笉瀛樺湪锛�

    # 闇�瑕佽�剧��CR0涓�鐨勫崗澶勭悊鍣ㄤ豢鐪熶��EM锛堜綅2锛夛紝骞跺�嶄綅鍗忓�勭悊鍣ㄥ瓨鍦ㄦ爣蹇�MP锛堜綅1锛夈��

 

 43         movl %cr0,%eax             # check math chip

 44         andl $0x80000011,%eax      # Save PG,PE,ET

 45 /* "orl $0x10020,%eax" here for 486 might be good */

 46         orl $2,%eax                # set MP

 47         movl %eax,%cr0

 48         call check_x87

 49         jmp after_page_tables      # 璺宠浆鍒�135琛屻��

 50

 51 /*

 52  * We depend on ET to be correct. This checks for 287/387.

 53  */

    /*

     * 鎴戜滑渚濊禆浜�ET鏍囧織鐨勬�ｇ‘鎬ф潵妫�娴�287/387瀛樺湪涓庡惁銆�

     */

    # 涓嬮潰fninit鍜�fstsw鏄�鏁板�﹀崗澶勭悊鍣�锛�80287/80387锛夌殑鎸囦护銆�

    # finit 鍚戝崗澶勭悊鍣ㄥ彂鍑哄垵濮嬪寲鍛戒护锛屽畠浼氭妸鍗忓�勭悊鍣ㄧ疆浜庝竴涓�鏈�鍙椾互鍓嶆搷浣滃奖鍝嶇殑宸茬煡鐘舵�侊紝璁剧疆

    # 鍏舵帶鍒跺瓧涓洪粯璁ゅ�笺�佹竻闄ょ姸鎬佸瓧鍜屾墍鏈夋诞鐐规爤寮忓瘎瀛樺櫒銆傞潪绛夊緟褰㈠紡鐨勮繖鏉℃寚浠わ紙fninit锛夎繕浼氳��

    # 鍗忓�勭悊鍣ㄧ粓姝㈡墽琛屽綋鍓嶆�ｅ湪鎵ц�岀殑浠讳綍鍏堝墠鐨勭畻鏈�鎿嶄綔銆�fstsw 鎸囦护鍙栧崗澶勭悊鍣ㄧ殑鐘舵�佸瓧銆傚�傛灉绯�

    # 缁熶腑瀛樺湪鍗忓�勭悊鍣ㄧ殑璇濓紝閭ｄ箞鍦ㄦ墽琛屼��fninit鎸囦护鍚庡叾鐘舵�佸瓧浣庡瓧鑺傝偗瀹氫负0銆�

 

 54 check_x87:

 55         fninit                     # 鍚戝崗澶勭悊鍣ㄥ彂鍑哄垵濮嬪寲鍛戒护銆�

 56         fstsw %ax                  # 鍙栧崗澶勭悊鍣ㄧ姸鎬佸瓧鍒�ax瀵勫瓨鍣ㄤ腑銆�

 57         cmpb $0,%al                # 鍒濆�嬪寲鍚庣姸鎬佸瓧搴旇�ヤ��0锛屽惁鍒欒�存槑鍗忓�勭悊鍣ㄤ笉瀛樺湪銆�

 58         je 1f                      /* no coprocessor: have to set bits */

 59         movl %cr0,%eax             # 濡傛灉瀛樺湪鍒欏悜鍓嶈烦杞�鍒版爣鍙�1澶勶紝鍚﹀垯鏀瑰啓cr0銆�

 60         xorl $6,%eax               /* reset MP, set EM */

 61         movl %eax,%cr0

 62         ret

 

    # 涓嬮潰鏄�涓�姹囩紪璇�瑷�鎸囩ず绗︺�傚叾鍚�涔夋槸鎸囧瓨鍌ㄨ竟鐣屽�归綈璋冩暣銆�"2"琛ㄧず鎶婇殢鍚庣殑浠ｇ爜鎴栨暟鎹�鐨勫亸绉讳綅缃�

    # 璋冩暣鍒板湴鍧�鍊兼渶鍚�2姣旂壒浣嶄负闆剁殑浣嶇疆锛�2^2锛夛紝鍗虫寜4瀛楄妭鏂瑰紡瀵归綈鍐呭瓨鍦板潃銆備笉杩囩幇鍦�GNU as

    # 鐩存帴鏃跺啓鍑哄�归綈鐨勫�艰�岄潪2鐨勬�℃柟鍊间簡銆備娇鐢ㄨ�ユ寚绀虹�︾殑鐩�鐨勬槸涓轰簡鎻愰��32浣�CPU璁块棶鍐呭瓨涓�浠ｇ��

    # 鎴栨暟鎹�鐨勯�熷害鍜屾晥鐜囥�傚弬瑙佺▼搴忓悗鐨勮�︾粏璇存槑銆�

    # 涓嬮潰鐨勪袱涓�瀛楄妭鍊兼槸80287鍗忓�勭悊鍣ㄦ寚浠�fsetpm鐨勬満鍣ㄧ爜銆傚叾浣滅敤鏄�鎶�80287璁剧疆涓轰繚鎶ゆā寮忋��

    # 80387鏃犻渶璇ユ寚浠わ紝骞朵笖灏嗕細鎶婅�ユ寚浠ょ湅浣滄槸绌烘搷浣溿��

 

 63 .align 2

 64 1:      .byte 0xDB,0xE4            /* fsetpm for 287, ignored by 387 */  # 287鍗忓�勭悊鍣ㄧ爜銆�

 65         ret

 66

 67 /*

 68  *  setup_idt

 69  *

 70  *  sets up a idt with 256 entries pointing to

 71  *  ignore_int, interrupt gates. It then loads

 72  *  idt. Everything that wants to install itself

 73  *  in the idt-table may do so themselves. Interrupts

 74  *  are enabled elsewhere, when we can be relatively

 75  *  sure everything is ok. This routine will be over-

 76  *  written by the page tables.

 77  */

    /*

     * 涓嬮潰杩欐�垫槸璁剧疆涓�鏂�鎻忚堪绗﹁〃瀛愮▼搴� setup_idt

     *

     * 灏嗕腑鏂�鎻忚堪绗﹁��idt璁剧疆鎴愬叿鏈�256涓�椤癸紝骞堕兘鎸囧��ignore_int涓�鏂�闂ㄣ�傜劧鍚庡姞杞戒腑鏂�

     * 鎻忚堪绗﹁〃瀵勫瓨鍣�(鐢�lidt鎸囦护)銆傜湡姝ｅ疄鐢ㄧ殑涓�鏂�闂ㄤ互鍚庡啀瀹夎�呫�傚綋鎴戜滑鍦ㄥ叾浠栧湴鏂硅�や负涓�鍒�

     * 閮芥�ｅ父鏃跺啀寮�鍚�涓�鏂�銆傝�ュ瓙绋嬪簭灏嗕細琚�椤佃〃瑕嗙洊鎺夈��

     */

    # 涓�鏂�鎻忚堪绗﹁〃涓�鐨勯」铏界劧涔熸��8瀛楄妭缁勬垚锛屼絾鍏舵牸寮忎笌鍏ㄥ眬琛ㄤ腑鐨勪笉鍚岋紝琚�绉颁负闂ㄦ弿杩扮��

    # (Gate Descriptor)銆傚畠鐨�0-1,6-7瀛楄妭鏄�鍋忕Щ閲忥��2-3瀛楄妭鏄�閫夋嫨绗︼紝4-5瀛楄妭鏄�涓�浜涙爣蹇椼��

    # 杩欐�典唬鐮侀�栧厛鍦�edx銆�eax涓�缁勫悎璁剧疆鍑�8瀛楄妭榛樿�ょ殑涓�鏂�鎻忚堪绗﹀�硷紝鐒跺悗鍦�idt琛ㄦ瘡涓�椤逛腑

    # 閮芥斁缃�璇ユ弿杩扮�︼紝鍏�256椤广��eax鍚�鏈夋弿杩扮�︿綆4瀛楄妭锛�edx鍚�鏈夐��4瀛楄妭銆傚唴鏍稿湪闅忓悗鐨勫垵濮�

    # 鍖栬繃绋嬩腑浼氭浛鎹㈠畨瑁呴偅浜涚湡姝ｅ疄鐢ㄧ殑涓�鏂�鎻忚堪绗﹂」銆�

 

 78 setup_idt:

 79         lea ignore_int,%edx        # 灏�ignore_int鐨勬湁鏁堝湴鍧�锛堝亸绉诲�硷級鍊�猫edx瀵勫瓨鍣�

 80         movl $0x00080000,%eax      # 灏嗛�夋嫨绗�0x0008缃�鍏�eax鐨勯珮16浣嶄腑銆�

 81         movw %dx,%ax               /* selector = 0x0008 = cs */

                                       # 鍋忕Щ鍊肩殑浣�16浣嶇疆鍏�eax鐨勪綆16浣嶄腑銆傛�ゆ��eax鍚�鏈�

                                       # 闂ㄦ弿杩扮�︿��4瀛楄妭鐨勫�笺��

 82         movw $0x8E00,%dx           /* interrupt gate - dpl=0, present */

 83                                    # 姝ゆ椂edx鍚�鏈夐棬鎻忚堪绗﹂��4瀛楄妭鐨勫�笺��

 84         lea _idt,%edi              # _idt鏄�涓�鏂�鎻忚堪绗﹁〃鐨勫湴鍧�銆�

 85         mov $256,%ecx

 86 rp_sidt:

 87         movl %eax,(%edi)           # 灏嗗搼涓�鏂�闂ㄦ弿杩扮�﹀瓨鍏ヨ〃涓�銆�

 88         movl %edx,4(%edi)          # eax鍐呭�规斁鍒� edi+4 鎵�鎸囧唴瀛樹綅缃�澶勩��

 89         addl $8,%edi               # edi鎸囧悜琛ㄤ腑涓嬩竴椤广��

 90         dec %ecx

 91         jne rp_sidt

 92         lidt idt_descr             # 鍔犺浇涓�鏂�鎻忚堪绗﹁〃瀵勫瓨鍣ㄥ�笺��

 93         ret

 94

 95 /*

 96  *  setup_gdt

 97  *

 98  *  This routines sets up a new gdt and loads it.

 99  *  Only two entries are currently built, the same

100  *  ones that were built in init.s. The routine

101  *  is VERY complicated at two whole lines, so this

102  *  rather long comment is certainly needed :-).

103  *  This routine will beoverwritten by the page tables.

104  */

    /*

     * 璁剧疆鍏ㄥ眬鎻忚堪绗﹁〃椤� setup_gdt

     * 杩欎釜瀛愮▼搴忚�剧疆涓�涓�鏂扮殑鍏ㄥ眬鎻忚堪绗﹁〃gdt锛屽苟鍔犺浇銆傛�ゆ椂浠呭垱寤轰簡涓や釜琛ㄩ」锛屼笌鍓�

     * 闈㈢殑涓�鏍枫�傝�ュ瓙绋嬪簭鍙�鏈変袱琛岋紝鈥滈潪甯哥殑鈥濆�嶆潅锛屾墍浠ュ綋鐒堕渶瑕佽繖涔堥暱鐨勬敞閲婁簡J銆�

     * 璇ュ瓙绋嬪簭灏嗚��椤佃〃瑕嗙洊鎺夈��

     */

105 setup_gdt:

106         lgdt gdt_descr             # 鍔犺浇鍏ㄥ眬鎻忚堪绗﹁〃瀵勫瓨鍣�(鍐呭�瑰凡璁剧疆濂斤紝瑙�234-238琛�)銆�

107         ret

108

109 /*

110  * I put the kernel page tables right after the page directory,

111  * using 4 of them to span 16 Mb of physical memory. People with

112  * more than 16MB will have to expand this.

113  */

    /* Linus灏嗗唴鏍哥殑鍐呭瓨椤佃〃鐩存帴鏀惧湪椤电洰褰曚箣鍚庯紝浣跨敤浜�4涓�琛ㄦ潵瀵诲潃16 MB鐨勭墿鐞嗗唴瀛樸��

     * 濡傛灉浣犳湁澶氫簬16 Mb鐨勫唴瀛橈紝灏遍渶瑕佸湪杩欓噷杩涜�屾墿鍏呬慨鏀广��

     */

     # 姣忎釜椤佃〃闀夸负4 Kb瀛楄妭锛�1椤靛唴瀛橀〉闈�锛夛紝鑰屾瘡涓�椤佃〃椤归渶瑕�4涓�瀛楄妭锛屽洜姝や竴涓�椤佃〃鍏卞彲浠ュ瓨鏀�

     # 1024涓�琛ㄩ」銆傚�傛灉涓�涓�椤佃〃椤瑰�诲潃4 KB鐨勫湴鍧�绌洪棿锛屽垯涓�涓�椤佃〃灏卞彲浠ュ�诲潃4 MB鐨勭墿鐞嗗唴瀛樸��

     # 椤佃〃椤圭殑鏍煎紡涓猴細椤圭殑鍓�0-11浣嶅瓨鏀句竴浜涙爣蹇楋紝渚嬪�傛槸鍚﹀湪鍐呭瓨涓�(P浣�0)銆佽�诲啓璁稿��(R/W浣�1)銆�

     # 鏅�閫氱敤鎴疯繕鏄�瓒呯骇鐢ㄦ埛浣跨��(U/S浣�2)銆佹槸鍚︿慨鏀硅繃(鏄�鍚﹁剰浜�)(D浣�6)绛夛紱琛ㄩ」鐨勪綅12-31鏄�

     # 椤垫�嗗湴鍧�锛岀敤浜庢寚鍑轰竴椤靛唴瀛樼殑鐗╃悊璧峰�嬪湴鍧�銆�

 

114 .org 0x1000      # 浠庡亸绉�0x1000澶勫紑濮嬫槸绗�1涓�椤佃〃锛堝亸绉�0寮�濮嬪�勫皢瀛樻斁椤佃〃鐩�褰曪級銆�

115 pg0:

116

117 .org 0x2000

118 pg1:

119

120 .org 0x3000

121 pg2:

122

123 .org 0x4000

124 pg3:

125

126 .org 0x5000        # 瀹氫箟涓嬮潰鐨勫唴瀛樻暟鎹�鍧椾粠鍋忕��0x5000澶勫紑濮嬨��

127 /*

128  * tmp_floppy_area is used by the floppy-driver when DMA cannot

129  * reach to a buffer-block. It needs to be aligned, so that it isn't

130  * on a 64kB border.

131  */

    /* 褰�DMA锛堢洿鎺ュ瓨鍌ㄥ櫒璁块棶锛変笉鑳借�块棶缂撳啿鍧楁椂锛屼笅闈㈢��tmp_floppy_area鍐呭瓨鍧�

     * 灏卞彲渚涜蒋鐩橀┍鍔ㄧ▼搴忎娇鐢ㄣ�傚叾鍦板潃闇�瑕佸�归綈璋冩暣锛岃繖鏍峰氨涓嶄細璺ㄨ��64KB杈圭晫銆�

     */

132 _tmp_floppy_area:

133         .fill 1024,1,0             # 鍏变繚鐣�1024椤癸紝姣忛」1瀛楄妭锛屽～鍏呮暟鍊�0銆�

134

    # 涓嬮潰杩欏嚑涓�鍏ユ爤鎿嶄綔鐢ㄤ簬涓鸿烦杞�鍒�init/main.c涓�鐨�main()鍑芥暟浣滃噯澶囧伐浣溿�傜��139琛屼笂

    # 鐨勬寚浠ゅ湪鏍堜腑鍘嬪叆浜嗚繑鍥炲湴鍧�锛岃�岀��140琛屽垯鍘嬪叆浜�main()鍑芥暟浠ｇ爜鐨勫湴鍧�銆傚綋head.s

    # 鏈�鍚庡湪绗�218琛屾墽琛�ret鎸囦护鏃跺氨浼氬脊鍑�main()鐨勫湴鍧�锛屽苟鎶婃帶鍒舵潈杞�绉诲��init/main.c

    # 绋嬪簭涓�銆傚弬瑙佺��3绔犱腑鏈夊叧C鍑芥暟璋冪敤鏈哄埗鐨勮�存槑銆�

    # 鍓嶉潰3涓�鍏ユ��0鍊煎簲璇ュ垎鍒�琛ㄧ��envp銆�argv鎸囬拡鍜�argc鐨勫�硷紝浣�main()娌℃湁鐢ㄥ埌銆�

    # 139琛岀殑鍏ユ爤鎿嶄綔鏄�妯℃嫙璋冪��main.c绋嬪簭鏃堕�栧厛灏嗚繑鍥炲湴鍧�鍏ユ爤鐨勬搷浣滐紝鎵�浠ュ�傛��

    # main.c绋嬪簭鐪熺殑閫�鍑烘椂锛屽氨浼氳繑鍥炲埌杩欓噷鐨勬爣鍙�L6澶勭户缁�鎵ц�屼笅鍘伙紝涔熷嵆姝诲惊鐜�銆�

    # 140琛屽皢main.c鐨勫湴鍧�鍘嬪叆鍫嗘爤锛岃繖鏍凤紝鍦ㄨ�剧疆鍒嗛〉澶勭悊锛�setup_paging锛夌粨鏉熷悗

    # 鎵ц��'ret'杩斿洖鎸囦护鏃跺氨浼氬皢main.c绋嬪簭鐨勫湴鍧�寮瑰嚭鍫嗘爤锛屽苟鍘绘墽琛�main.c绋嬪簭浜嗐��

    # 鏈夊叧C鍑芥暟璋冪敤鏈哄埗璇峰弬瑙佺▼搴忓悗鐨勮�存槑銆�

135 after_page_tables:

136         pushl $0                   # These are the parameters to main :-)

137         pushl $0                   # 杩欎簺鏄�璋冪��main绋嬪簭鐨勫弬鏁帮紙鎸�init/main.c锛夈��

138         pushl $0                   # 鍏朵腑鐨�'$'绗﹀彿琛ㄧず杩欐槸涓�涓�绔嬪嵆鎿嶄綔鏁般��

139         pushl $L6                  # return address for main, if it decides to.

140         pushl $_main               # '_main'鏄�缂栬瘧绋嬪簭瀵�main鐨勫唴閮ㄨ〃绀烘柟娉曘��

141         jmp setup_paging           # 璺宠浆鑷崇��198琛屻��

142 L6:

143         jmp L6                     # main should never return here, but

144                                    # just in case, we know what happens.

                                       # main绋嬪簭缁濆�逛笉搴旇�ヨ繑鍥炲埌杩欓噷銆備笉杩囦负浜嗕互闃蹭竾涓�锛�

                                       # 鎵�浠ユ坊鍔犱簡璇ヨ��鍙ャ�傝繖鏍锋垜浠�灏辩煡閬撳彂鐢熶粈涔堥棶棰樹簡銆�

145

146 /* This is the default interrupt "handler" :-) */

    /* 涓嬮潰鏄�榛樿�ょ殑涓�鏂�鈥滃悜閲忓彞鏌勨��J */

147 int_msg:

148         .asciz "Unknown interrupt\n\r"     # 瀹氫箟瀛楃�︿覆鈥滄湭鐭ヤ腑鏂�(鍥炶溅鎹㈣��)鈥濄��

149 .align 2                   # 鎸�4瀛楄妭鏂瑰紡瀵归綈鍐呭瓨鍦板潃銆�

150 ignore_int:

151         pushl %eax

152         pushl %ecx

153         pushl %edx

154         push %ds           # 杩欓噷璇锋敞鎰忥紒锛�ds,es,fs,gs绛夎櫧鐒舵槸16浣嶇殑瀵勫瓨鍣�锛屼絾鍏ユ爤鍚�

155         push %es           # 浠嶇劧浼氫互32浣嶇殑褰㈠紡鍏ユ爤锛屼篃鍗抽渶瑕佸崰鐢�4涓�瀛楄妭鐨勫爢鏍堢┖闂淬��

156         push %fs

157         movl $0x10,%eax    # 缃�娈甸�夋嫨绗︼紙浣�ds,es,fs鎸囧悜gdt琛ㄤ腑鐨勬暟鎹�娈碉級銆�

158         mov %ax,%ds

159         mov %ax,%es

160         mov %ax,%fs

161         pushl $int_msg     # 鎶婅皟鐢�printk鍑芥暟鐨勫弬鏁版寚閽堬紙鍦板潃锛夊叆鏍堛�傛敞鎰忥紒鑻�int_msg

162         call _printk       # 鍓嶄笉鍔�'$'锛屽垯琛ㄧず鎶�int_msg绗﹀彿澶勭殑闀垮瓧锛�'Unkn'锛夊叆鏍�J銆�

163         popl %eax          # 璇ュ嚱鏁板湪/kernel/printk.c涓�銆�'_printk'鏄�printk缂栬瘧鍚庢ā鍧椾腑

164         pop %fs            # 鐨勫唴閮ㄨ〃绀烘硶銆�

165         pop %es

166         pop %ds

167         popl %edx

168         popl %ecx

169         popl %eax

170         iret           # 涓�鏂�杩斿洖锛堟妸涓�鏂�璋冪敤鏃跺帇鍏ユ爤鐨�CPU鏍囧織瀵勫瓨鍣�锛�32浣嶏級鍊间篃寮瑰嚭锛夈��

171

172

173 /*

174  * Setup_paging

175  *

176  * This routine sets up paging by setting the page bit

177  * in cr0. The page tables are set up, identity-mapping

178  * the first 16MB. The pager assumes that no illegal

179  * addresses are produced (ie >4Mb on a 4Mb machine).

180  *

181  * NOTE! Although all physical memory should be identity

182  * mapped by this routine, only the kernel page functions

183  * use the >1Mb addresses directly. All "normal" functions

184  * use just the lower 1Mb, or the local data space, which

185  * will be mapped to some other place - mm keeps track of

186  * that.

187  *

188  * For those with more memory than 16 Mb - tough luck. I've

189  * not got it, why should you :-) The source is here. Change

190  * it. (Seriously - it shouldn't be too difficult. Mostly

191  * change some constants etc. I left it at 16Mb, as my machine

192  * even cannot be extended past that (ok, but it was cheap :-)

193  * I've tried to show which constants to change by having

194  * some kind of marker at them (search for "16Mb"), but I

195  * won't guarantee that's all :-( )

196  */

    /*

     * 杩欎釜瀛愮▼搴忛�氳繃璁剧疆鎺у埗瀵勫瓨鍣�cr0鐨勬爣蹇楋紙PG 浣�31锛夋潵鍚�鍔ㄥ�瑰唴瀛樼殑鍒嗛〉澶勭悊鍔熻兘锛�

     * 骞惰�剧疆鍚勪釜椤佃〃椤圭殑鍐呭�癸紝浠ユ亽绛夋槧灏勫墠16 MB鐨勭墿鐞嗗唴瀛樸�傚垎椤靛櫒鍋囧畾涓嶄細浜х敓闈炴硶鐨�

     * 鍦板潃鏄犲皠锛堜篃鍗冲湪鍙�鏈�4Mb鐨勬満鍣ㄤ笂璁剧疆鍑哄ぇ浜�4Mb鐨勫唴瀛樺湴鍧�锛夈��

     *

     * 娉ㄦ剰锛佸敖绠℃墍鏈夌殑鐗╃悊鍦板潃閮藉簲璇ョ敱杩欎釜瀛愮▼搴忚繘琛屾亽绛夋槧灏勶紝浣嗗彧鏈夊唴鏍搁〉闈㈢�＄悊鍑芥暟鑳�

     * 鐩存帴浣跨敤>1Mb鐨勫湴鍧�銆傛墍鏈夆�滄櫘閫氣�濆嚱鏁颁粎浣跨敤浣庝簬1Mb鐨勫湴鍧�绌洪棿锛屾垨鑰呮槸浣跨敤灞�閮ㄦ暟鎹�

     * 绌洪棿锛岃�ュ湴鍧�绌洪棿灏嗚��鏄犲皠鍒板叾浠栦竴浜涘湴鏂瑰幓 -- mm锛堝唴瀛樼�＄悊绋嬪簭锛変細绠＄悊杩欎簺浜嬬殑銆�

     *

     * 瀵逛簬閭ｄ簺鏈夊�氫��16Mb鍐呭瓨鐨勫�朵�� 鈥� 鐪熸槸澶�骞歌繍浜嗭紝鎴戣繕娌℃湁锛屼负浠�涔堜綘浼氭湁J銆備唬鐮佸氨鍦�

     * 杩欓噷锛屽�瑰畠杩涜�屼慨鏀瑰惂銆傦紙瀹為檯涓婏紝杩欏苟涓嶅お鍥伴毦鐨勩�傞�氬父鍙�闇�淇�鏀逛竴浜涘父鏁扮瓑銆傛垜鎶婂畠璁剧疆

     * 涓�16Mb锛屽洜涓烘垜鐨勬満鍣ㄥ啀鎬庝箞鎵╁厖鐢氳嚦涓嶈兘瓒呰繃杩欎釜鐣岄檺锛堝綋鐒讹紝鎴戠殑鏈哄櫒鏄�寰堜究瀹滅��J锛夈��

     * 鎴戝凡缁忛�氳繃璁剧疆鏌愮被鏍囧織鏉ョ粰鍑洪渶瑕佹敼鍔ㄧ殑鍦版柟锛堟悳绱⑩��16Mb鈥�锛夛紝浣嗘垜涓嶈兘淇濊瘉浣滆繖浜�

     * 鏀瑰姩灏辫�屼��L锛夈��

     */

    # 涓婇潰鑻辨枃娉ㄩ噴绗�2娈电殑鍚�涔夋槸鎸囧湪鏈哄櫒鐗╃悊鍐呭瓨涓�澶т簬1MB鐨勫唴瀛樼┖闂翠富瑕佽��鐢ㄤ簬涓诲唴瀛樺尯銆�

    # 涓诲唴瀛樺尯绌洪棿鐢�mm妯″潡绠＄悊銆傚畠娑夊強鍒伴〉闈㈡槧灏勬搷浣溿�傚唴鏍镐腑鎵�鏈夊叾浠栧嚱鏁板氨鏄�杩欓噷鎸囩殑涓�鑸�

    #锛堟櫘閫氾級鍑芥暟銆傝嫢瑕佷娇鐢ㄤ富鍐呭瓨鍖虹殑椤甸潰锛屽氨闇�瑕佷娇鐢�get_free_page()绛夊嚱鏁拌幏鍙栥�傚洜涓轰富鍐�

    # 瀛樺尯涓�鍐呭瓨椤甸潰鏄�鍏变韩璧勬簮锛屽繀椤绘湁绋嬪簭杩涜�岀粺涓�绠＄悊浠ラ伩鍏嶈祫婧愪簤鐢ㄥ拰绔炰簤銆�

    #

    # 鍦ㄥ唴瀛樼墿鐞嗗湴鍧�0x0澶勫紑濮嬪瓨鏀�1椤甸〉鐩�褰曡〃鍜�4椤甸〉琛ㄣ�傞〉鐩�褰曡〃鏄�绯荤粺鎵�鏈夎繘绋嬪叕鐢ㄧ殑锛岃��

    # 杩欓噷鐨�4椤甸〉琛ㄥ垯灞炰簬鍐呮牳涓撶敤锛屽畠浠�涓�涓�鏄犲皠绾挎�у湴鍧�璧峰��16MB绌洪棿鑼冨洿鍒扮墿鐞嗗唴瀛樹笂銆傚�逛��

    # 鏂扮殑杩涚▼锛岀郴缁熶細鍦ㄤ富鍐呭瓨鍖轰负鍏剁敵璇烽〉闈㈠瓨鏀鹃〉琛ㄣ�傚彟澶栵紝1椤靛唴瀛橀暱搴︽槸4096瀛楄妭銆�

 

197 .align 2                           # 鎸�4瀛楄妭鏂瑰紡瀵归綈鍐呭瓨鍦板潃杈圭晫銆�

198 setup_paging:                      # 棣栧厛瀵�5椤靛唴瀛橈紙1椤电洰褰� + 4椤甸〉琛�锛夋竻闆躲��

199         movl $1024*5,%ecx          /* 5 pages - pg_dir+4 page tables */

200         xorl %eax,%eax

201         xorl %edi,%edi             /* pg_dir is at 0x000 */

                                       # 椤电洰褰曚粠0x000鍦板潃寮�濮嬨��

202         cld;rep;stosl              # eax鍐呭�瑰瓨鍒�es:edi鎵�鎸囧唴瀛樹綅缃�澶勶紝涓�edi澧�4銆�

 

    # 涓嬮潰4鍙ヨ�剧疆椤电洰褰曡〃涓�鐨勯」锛屽洜涓烘垜浠�锛堝唴鏍革級鍏辨��4涓�椤佃〃鎵�浠ュ彧闇�璁剧疆4椤广��

    # 椤电洰褰曢」鐨勭粨鏋勪笌椤佃〃涓�椤圭殑缁撴瀯涓�鏍凤紝4涓�瀛楄妭涓�1椤广�傚弬瑙佷笂闈�113琛屼笅鐨勮�存槑銆�

    # 渚嬪��"$pg0+7"琛ㄧず锛�0x00001007锛屾槸椤电洰褰曡〃涓�鐨勭��1椤广��

    # 鍒欑��1涓�椤佃〃鎵�鍦ㄧ殑鍦板潃 = 0x00001007 & 0xfffff000 = 0x1000锛�

    # 绗�1涓�椤佃〃鐨勫睘鎬ф爣蹇� = 0x00001007 & 0x00000fff = 0x07锛岃〃绀鸿�ラ〉瀛樺湪銆佺敤鎴峰彲璇诲啓銆�

203         movl $pg0+7,_pg_dir        /* set present bit/user r/w */

204         movl $pg1+7,_pg_dir+4      /*  --------- " " --------- */

205         movl $pg2+7,_pg_dir+8      /*  --------- " " --------- */

206         movl $pg3+7,_pg_dir+12     /*  --------- " " --------- */

 

    # 涓嬮潰6琛屽～鍐�4涓�椤佃〃涓�鎵�鏈夐」鐨勫唴瀹癸紝鍏辨湁锛�4(椤佃〃)*1024(椤�/椤佃〃)=4096椤�(0 - 0xfff)锛�

    # 涔熷嵆鑳芥槧灏勭墿鐞嗗唴瀛� 4096*4Kb = 16Mb銆�

    # 姣忛」鐨勫唴瀹规槸锛氬綋鍓嶉」鎵�鏄犲皠鐨勭墿鐞嗗唴瀛樺湴鍧� + 璇ラ〉鐨勬爣蹇楋紙杩欓噷鍧囦负7锛夈��

    # 浣跨敤鐨勬柟娉曟槸浠庢渶鍚庝竴涓�椤佃〃鐨勬渶鍚庝竴椤瑰紑濮嬫寜鍊掗��椤哄簭濉�鍐欍�備竴涓�椤佃〃鐨勬渶鍚庝竴椤瑰湪椤佃〃涓�鐨�

    # 浣嶇疆鏄�1023*4 = 4092銆傚洜姝ゆ渶鍚庝竴椤电殑鏈�鍚庝竴椤圭殑浣嶇疆灏辨槸$pg3+4092銆�

 

207         movl $pg3+4092,%edi        # edi猫鏈�鍚庝竴椤电殑鏈�鍚庝竴椤广��

208         movl $0xfff007,%eax        /*  16Mb - 4096 + 7 (r/w user,p) */

                                       # 鏈�鍚�1椤瑰�瑰簲鐗╃悊鍐呭瓨椤甸潰鐨勫湴鍧�鏄�0xfff000锛�

                                       # 鍔犱笂灞炴�ф爣蹇�7锛屽嵆涓�0xfff007銆�

209         std                        # 鏂瑰悜浣嶇疆浣嶏紝edi鍊奸�掑噺(4瀛楄妭)銆�

210 1:      stosl                      /* fill pages backwards - more efficient :-) */

211         subl $0x1000,%eax          # 姣忓～鍐欏ソ涓�椤癸紝鐗╃悊鍦板潃鍊煎噺0x1000銆�

212         jge 1b                     # 濡傛灉灏忎簬0鍒欒�存槑鍏ㄦ坊鍐欏ソ浜嗐��

    # 璁剧疆椤电洰褰曡〃鍩哄潃瀵勫瓨鍣�cr3鐨勫�硷紝鎸囧悜椤电洰褰曡〃銆�cr3涓�淇濆瓨鐨勬槸椤电洰褰曡〃鐨勭墿鐞嗗湴鍧�銆�

213         xorl %eax,%eax             /* pg_dir is at 0x0000 */   # 椤电洰褰曡〃鍦�0x0000澶勩��

214         movl %eax,%cr3             /* cr3 - page directory start */

    # 璁剧疆鍚�鍔ㄤ娇鐢ㄥ垎椤靛�勭悊锛�cr0鐨�PG鏍囧織锛屼綅31锛�

215         movl %cr0,%eax

216         orl $0x80000000,%eax       # 娣讳笂PG鏍囧織銆�

217         movl %eax,%cr0             /* set paging (PG) bit */

218         ret                        /* this also flushes prefetch-queue */

 

    # 鍦ㄦ敼鍙樺垎椤靛�勭悊鏍囧織鍚庤�佹眰浣跨敤杞�绉绘寚浠ゅ埛鏂伴�勫彇鎸囦护闃熷垪锛岃繖閲岀敤鐨勬槸杩斿洖鎸囦护ret銆�

    # 璇ヨ繑鍥炴寚浠ょ殑鍙︿竴涓�浣滅敤鏄�灏�140琛屽帇鍏ュ爢鏍堜腑鐨�main绋嬪簭鐨勫湴鍧�寮瑰嚭锛屽苟璺宠浆鍒�/init/main.c

    # 绋嬪簭鍘昏繍琛屻�傛湰绋嬪簭鍒版�ゅ氨鐪熸�ｇ粨鏉熶簡銆�

 

219

220 .align 2                           # 鎸�4瀛楄妭鏂瑰紡瀵归綈鍐呭瓨鍦板潃杈圭晫銆�

221 .word 0                            # 杩欓噷鍏堢┖鍑�2瀛楄妭锛岃繖鏍�224琛屼笂鐨勯暱瀛楁槸4瀛楄妭瀵归綈鐨勩��

 

    ! 涓嬮潰鏄�鍔犺浇涓�鏂�鎻忚堪绗﹁〃瀵勫瓨鍣�idtr鐨勬寚浠�lidt瑕佹眰鐨�6瀛楄妭鎿嶄綔鏁般�傚墠2瀛楄妭鏄�idt琛ㄧ殑闄愰暱锛�

    ! 鍚�4瀛楄妭鏄�idt琛ㄥ湪绾挎�у湴鍧�绌洪棿涓�鐨�32浣嶅熀鍦板潃銆�

222 idt_descr:

223         .word 256*8-1              # idt contains 256 entries  # 鍏�256椤癸紝闄愰暱=闀垮害 - 1銆�

224         .long _idt

225 .align 2

226 .word 0

 

    ! 涓嬮潰鍔犺浇鍏ㄥ眬鎻忚堪绗﹁〃瀵勫瓨鍣�gdtr鐨勬寚浠�lgdt瑕佹眰鐨�6瀛楄妭鎿嶄綔鏁般�傚墠2瀛楄妭鏄�gdt琛ㄧ殑闄愰暱锛�

    ! 鍚�4瀛楄妭鏄�gdt琛ㄧ殑绾挎�у熀鍦板潃銆傝繖閲屽叏灞�琛ㄩ暱搴﹁�剧疆涓�2KB瀛楄妭锛�0x7ff鍗冲彲锛夛紝鍥犱负姣�8瀛楄妭

    ! 缁勬垚涓�涓�鎻忚堪绗﹂」锛屾墍浠ヨ〃涓�鍏卞彲鏈�256椤广�傜�﹀��_gdt鏄�鍏ㄥ眬琛ㄥ湪鏈�绋嬪簭涓�鐨勫亸绉讳綅缃�锛岃��234琛屻��

227 gdt_descr:

228         .word 256*8-1              # so does gdt (not that that's any   # 娉�锛�not 脿 note

229         .long _gdt                 # magic number, but it works for me :^)

230

231         .align 3                   # 鎸�8锛�2^3锛夊瓧鑺傛柟寮忓�归綈鍐呭瓨鍦板潃杈圭晫銆�

232 _idt:   .fill 256,8,0              # idt is uninitialized   # 256椤癸紝姣忛」8瀛楄妭锛屽～0銆�

233

    # 鍏ㄥ眬琛ㄣ�傚墠4椤瑰垎鍒�鏄�绌洪」锛堜笉鐢�锛夈�佷唬鐮佹�垫弿杩扮�︺�佹暟鎹�娈垫弿杩扮�︺�佺郴缁熻皟鐢ㄦ�垫弿杩扮�︼紝鍏朵腑

    # 绯荤粺璋冪敤娈垫弿杩扮�﹀苟娌℃湁娲剧敤澶勶��Linus褰撴椂鍙�鑳芥浘鎯虫妸绯荤粺璋冪敤浠ｇ爜涓撻棬鏀惧湪杩欎釜鐙�绔嬬殑娈典腑銆�

    # 鍚庨潰杩橀�勭暀浜�252椤圭殑绌洪棿锛岀敤浜庢斁缃�鎵�鍒涘缓浠诲姟鐨勫眬閮ㄦ弿杩扮��(LDT)鍜屽�瑰簲鐨勪换鍔＄姸鎬佹��TSS

    # 鐨勬弿杩扮�︺��

    # (0-nul, 1-cs, 2-ds, 3-syscall, 4-TSS0, 5-LDT0, 6-TSS1, 7-LDT1, 8-TSS2 etc...)

 

234 _gdt:   .quad 0x0000000000000000        /* NULL descriptor */

235         .quad 0x00c09a0000000fff        /* 16Mb */      # 0x08锛屽唴鏍镐唬鐮佹�垫渶澶ч暱搴�16MB銆�

236         .quad 0x00c0920000000fff        /* 16Mb */      # 0x10锛屽唴鏍告暟鎹�娈垫渶澶ч暱搴�16MB銆�

237         .quad 0x0000000000000000        /* TEMPORARY - don't use */

238         .fill 252,8,0                   /* space for LDT's and TSS's etc */  # 棰勭暀绌洪棿銆�