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[WIP] Get bare metal working outside of an emulator (#609)

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You can now run bare metal on bare metal!

* Fix handling of int 0x15 eax = 0xe820 memory map
* Fix some issues in initial page table creation
* hello4.com now works outside emulators
* Ensure area for identity page tables are zeroed first
* Simplify logic for creating page table entries, this partly
  reverts 577c0f6226
* Add degenerate MBR partition entry, to ease testing

Co-authored-by: tkchia <tkchia-cosmo@gmx.com>
This commit is contained in:
tkchia 2022-09-13 17:01:49 +08:00 • committed by Justine Tunney
parent c03359c637
commit 116bda997e
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GPG key ID: BE714B4575D6E328
3 changed files with 55 additions and 35 deletions
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67
ape/ape.S
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@ -329,7 +329,7 @@ dsknfo: push %bx
movpp %es,%ds
xor %si,%si
mov %si,%es
mov $0x1510,%si # mman::pc_drive_base_table
mov $0x1d10,%si # mman::pc_drive_base_table
xchg %si,%di
movsw #→ headunloadtime, headloadtime
movsw #→ shutofftime, bytespersector
@ -382,11 +382,11 @@ pcread: push %ax
add $512>>4,%si
mov %si,%es
inc %al # ++sector
cmp 0x151c,%al # mman::pc_drive_last_sector
cmp 0x1d1c,%al # mman::pc_drive_last_sector
jbe 2f
mov $1,%al
inc %dh # ++head
cmp 0x1520,%dh # mman::pc_drive_last_head
cmp 0x1d20,%dh # mman::pc_drive_last_head
jbe 2f
xor %dh,%dh
inc %cx # ++cylinder
@ -485,19 +485,19 @@ ape.mbrpad:
ape_disk:
.stub ape.diskid,quad
.org 0x1be,0x00
.macro .partn x
.stub ape.part\x\().status,byte # 0=absent / 0x80=present
.stub ape.part\x\().first.head,byte # in low 6 bits
.stub ape.part\x\().first.cylinder,byte
.stub ape.part\x\().first.sector,byte
.stub ape.part\x\().filesystem,byte
.stub ape.part\x\().last.head,byte
.stub ape.part\x\().last.cylinder,byte
.stub ape.part\x\().last.sector,byte
.stub ape.part\x\().lba,long # c₀*Cₙ + h₀*Hₙ + s₀*Sₙ
.stub ape.part\x\().sector.count,long # sectors are 512 bytes
.macro .partn x:req sta h0 s0 c0 fs h9 s9 c9 lba0 nsec
.stub ape.part\x\().status,byte,\sta # 0=non-boot / 0x80=active
.stub ape.part\x\().first.head,byte,\h0
.stub ape.part\x\().first.sector,byte,\s0 # in low 6 bits
.stub ape.part\x\().first.cylinder,byte,\c0
.stub ape.part\x\().filesystem,byte,\fs
.stub ape.part\x\().last.head,byte,\h9
.stub ape.part\x\().last.sector,byte,\s9
.stub ape.part\x\().last.cylinder,byte,\c9
.stub ape.part\x\().lba,long,\lba0 # c₀*Cₙ + h₀*Hₙ + s₀*Sₙ
.stub ape.part\x\().sector.count,long,\nsec # sectors are 512 bytes
.endm
.partn 1
.partn 1,0x80,0,1,0,0x7f,0xff,0xff,0xff,0,0xffffffff
.partn 2
.partn 3
.partn 4
@ -1291,27 +1291,38 @@ lcheck: pushf # check for i8086 / i8088 / i80186
// Gets memory map from BIOS.
e820: mov $0x0510>>4,%di # mman::e820
mov %di,%es
xor %edi,%edi # es:di is destination buffer
xor %di,%di # es:di is destination buffer
xor %ebx,%ebx # ebx is an api state tracker
1: mov $0xE820,%eax # magic
mov $8+8+4+4,%ecx # sizeof(struct SmapEntry)
mov $0x534d4150,%edx # magic number
movl $1,8+8+4/*SmapEntry::acpi3*/(%di) # prefill ACPI attributes;
# apparently some buggy BIOSes say
# that they return this field, yet
# do not fill it correctly
int $0x15 # ax,bx,cx,dx,di → ax,bx,cx
jc 9f # cf = unsupported or abuse
cmp %edx,%eax # more magic means success
jne 9f
test %cx,%cx # discard empty results
jz 5f
mov 8/*LODWORD(SmapEntry::size)*/(%di),%eax
or 8+4/*HIDWORD(SmapEntry::size)*/(%di),%eax
jz 5f
cmp $8+8+4+1,%cx # discard if ignore flag
jb 4f
testb $1/*ignore*/,8+8+4/*SmapEntry::__acpi3*/(%di)
jnz 5f
testb $1/*don't ignore*/,8+8+4/*SmapEntry::acpi3*/(%di)
jz 5f
4: add $8+8+4+4,%di # keep entry
5: test %ebx,%ebx # last entry?
jz 8f
cmp $0x1000,%di
cmp $(256-1)*(8+8+4+4),%di
jb 1b
8: ret
8: xor %ax,%ax # add a blank sentinel entry
mov $(8+8)/2,%cx
cld
rep stosw
ret
9: mov $REAL(str.e820),%di
call rldie
.endfn e820
@ -1381,9 +1392,16 @@ a20: cli
// Initializes long mode paging.
pinit: push %ds
push %es
#define SEG 0x79000
mov $SEG>>4,%ax
mov %ax,%ds
mov %ax,%es
xor %di,%di
xor %ax,%ax
mov $(0x7f000-SEG)/2,%cx
cld
rep stosw
movl $0x7d000+PAGE_V+PAGE_RW,0x7e000-SEG # PDPT←PML4T (+)
movl $0x7c000+PAGE_V+PAGE_RW,0x7e800-SEG # PDPT←PML4T (-)
movl $0x7b000+PAGE_V+PAGE_RW,0x7d000-SEG # PDT←PDPT (+)
@ -1392,13 +1410,14 @@ pinit: push %ds
movl $0x79000+PAGE_V+PAGE_RW,0x7a000-SEG # PD←PDT (-)
mov $512,%cx # PD±2MB
mov $PAGE_V+PAGE_RW,%eax
xor %si,%si
0: mov %eax,(%si)
xor %di,%di
0: stosl
add $0x1000,%eax
add $8,%si
scasl # di += 4
loop 0b
mov $0x7e000,%eax # PML4T←CR3
mov %eax,%cr3
pop %es
pop %ds
ret
.endfn pinit
@ -1407,7 +1426,7 @@ pinit: push %ds
//
// @see Intel Manual V3A §4.1.2
golong: cli
lidt 0x1522 # mman::bad_idt
lidt 0x1d22 # mman::bad_idt
mov %cr4,%eax
or $CR4_PAE|CR4_PGE|CR4_OSFXSR,%eax
mov %eax,%cr4