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| author | Kartik K. Agaram <vc@akkartik.com> | 2021-03-14 23:30:58 -0700 |
|---|---|---|
| committer | Kartik K. Agaram <vc@akkartik.com> | 2021-03-14 23:30:58 -0700 |
| commit | 4f7758fa1598c04062b24eee3afbec446ecd6b67 (patch) | |
| tree | 4f93eedbf37e2157f3e16015a54b08b124e57c68 | |
| parent | ee81002eb06285e3b13754e95d513f1ac79f4827 (diff) | |
| download | mu-4f7758fa1598c04062b24eee3afbec446ecd6b67.tar.gz | |
first use of the padding segment selector
| -rw-r--r-- | boot.subx | 31 |
1 files changed, 18 insertions, 13 deletions
diff --git a/boot.subx b/boot.subx index dd01f409..d1d8a3bc 100644 --- a/boot.subx +++ b/boot.subx @@ -164,7 +164,9 @@ 66 83 c8 01 # eax <- or 0x1 == code 0f 22/cr<- 3/mod/direct 0/rm32/cr0 0/r32/eax - # . far jump that sets cs to offset 8 in the gdt in the process + # far jump to initialize_32bit_mode that sets cs to offset 8 in the gdt in the process + # We can't refer to the label directly because SubX doesn't have syntax for + # segment selectors. So we pin initialize_32bit_mode instead below. ea/jump-far-absolute 0x00087d00/disp32 # address 0x7d00 in offset 8 of the gdt == data @@ -219,20 +221,21 @@ gdt_descriptor: 0x17/imm16 # final index of gdt = size of gdt - 1 gdt_start/imm32/start -# padding -# fe: - 00 00 - -## 32-bit code from this point (still some instructions not in SubX) +## 32-bit code from this point -# offset 100 (address 0x7d00): -# initialize_32bit_mode: +== code 0x7d00 +initialize_32bit_mode: +== data + # TODO: SubX doesn't understand 66 prefix 66 b8 10 00 # ax <- offset 16 from gdt_start - 8e d8 # ds <- ax - 8e d0 # ss <- ax - 8e c0 # es <- ax - 8e e0 # fs <- ax - 8e e8 # gs <- ax +== code + 8e/seg-> 3/mod/direct 0/rm32/ax 3/r32/ds + 8e/seg-> 3/mod/direct 0/rm32/ax 2/r32/ss + 8e/seg-> 3/mod/direct 0/rm32/ax 0/r32/es + 8e/seg-> 3/mod/direct 0/rm32/ax 4/r32/fs + 8e/seg-> 3/mod/direct 0/rm32/ax 5/r32/gs + +== data # 10e: bc 00 00 07 00 # esp <- 0x00070000 @@ -271,6 +274,8 @@ gdt_descriptor: e0 # 11/mod/direct 100/r32/CR4 000/rm32/eax e9 d0 16 00 00 # jump to 0x9400 [label] +== data + # padding # 130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |