#include?
#include?
#include?

/*?*********************************************************************
?*?This?a?dirt?simple?boot?loader?whose?sole?job?is?to?boot
?*?an?ELF?kernel?image?from?the?first?IDE?hard?disk.
?*
?*?DISK?LAYOUT
?*??*?This?program（bootasm.S?and?bootmain.c）?is?the?bootloader.
?*????It?should?be?stored?in?the?first?sector?of?the?disk.
?*
?*??*?The?2nd?sector?onward?holds?the?kernel?image.
?*
?*??*?The?kernel?image?must?be?in?ELF?format.
?*
?*?BOOT?UP?STEPS
?*??*?when?the?CPU?boots?it?loads?the?BIOS?into?memory?and?executes?it
?*
?*??*?the?BIOS?intializes?devices?sets?of?the?interrupt?routines?and
?*????reads?the?first?sector?of?the?boot?device（e.g.?hard-drive）
?*????into?memory?and?jumps?to?it.
?*
?*??*?Assuming?this?boot?loader?is?stored?in?the?first?sector?of?the
?*????hard-drive?this?code?takes?over...
?*
?*??*?control?starts?in?bootasm.S?--?which?sets?up?protected?mode
?*????and?a?stack?so?C?code?then?run?then?calls?bootmain（）
?*
?*??*?bootmain（）?in?this?file?takes?over?reads?in?the?kernel?and?jumps?to?it.
?*?*/

#define?SECTSIZE????????512
#define?ELFHDR??????????（（struct?elfhdr?*）0x10000）??????//?scratch?space

/*?waitdisk?-?wait?for?disk?ready?*/
static?void
waitdisk（void）?{
????while?（（inb（0x1F7）?&?0xC0）?!=?0x40）
????????/*?do?nothing?*/;
}

/*?readsect?-?read?a?single?sector?at?@secno?into?@dst?*/
static?void
readsect（void?*dst?uint32_t?secno）?{
????//?wait?for?disk?to?be?ready
????waitdisk（）;

????outb（0x1F2?1）;?????????????????????????//?count?=?1
????outb（0x1F3?secno?&?0xFF）;
????outb（0x1F4?（secno?>>?8）?&?0xFF）;
????outb（0x1F5?（secno?>>?16）?&?0xFF）;
????outb（0x1F6?（（secno?>>?24）?&?0xF）?|?0xE0）;
????outb（0x1F7?0x20）;??????????????????????//?cmd?0x20?-?read?sectors

????//?wait?for?disk?to?be?ready
????waitdisk（）;

????//?read?a?sector
????insl（0x1F0?dst?SECTSIZE?/?4）;
}

/*?*
?*?readseg?-?read?@count?bytes?at?@offset?from?kernel?into?virtual?address?@va
?*?might?copy?more?than?asked.
?*?*/
static?void
readseg（uintptr_t?va?uint32_t?count?uint32_t?offset）?{
????uintptr_t?end_va?=?va?+?count;

????//?round?down?to?sector?boundary
????va?-=?offset?%?SECTSIZE;

????//?translate?from?bytes?to?sectors;?kernel?starts?at?sector?1
????uint32_t?secno?=?（offset?/?SECTSIZE）?+?1;

????//?If?this?is?too?slow?we?could?read?lots?of?sectors?at?a?time.
????//?We‘d?write?more?to?memory?than?asked?but?it?doesn‘t?matter?--
????//?we?load?in?increasing?order.
????for?（;?va?????????readsect（（void?*）va?secno）;
????}
}

/*?bootmain?-?the?entry?of?bootloader?*/
void
bootmain（void）?{
????//?read?the?1st?page?off?disk
????readseg（（uintptr_t）ELFHDR?SECTSIZE?*?8?0）;

????//?is?this?a?valid?ELF?
????if?（ELFHDR->e_magic?!=?ELF_MAGIC）?{
????????goto?bad;
????}

????struct?proghdr?*ph?*eph;

????//?load?each?program?segment?（ignores?ph?flags）
????ph?=?（struct?proghdr?*）（（uintptr_t）ELFHDR?+?ELFHDR->e_phoff）;
????eph?=?ph?+?ELFHDR->e_phnum;
????for?（;?ph?