reorganize source

[com32] / src / kern / segm_s.asm

diff --git a/src/kern/segm_s.asm b/src/kern/segm_s.asm
new file mode 100644 (file)
index 0000000..6448c04
--- /dev/null
+++ b/src/kern/segm_s.asm
@@ -0,0 +1,64 @@
+; pcboot - bootable PC demo/game kernel
+; Copyright (C) 2018-2023  John Tsiombikas <nuclear@member.fsf.org>
+; 
+; This program is free software: you can redistribute it and/or modify
+; it under the terms of the GNU General Public License as published by
+; the Free Software Foundation, either version 3 of the License, or
+; (at your option) any later version.
+; 
+; This program is distributed in the hope that it will be useful,
+; but WITHOUT ANY WARRANTY, without even the implied warranty of
+; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+; GNU General Public License for more details.
+; 
+; You should have received a copy of the GNU General Public License
+; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+       section .data
+       align 4
+; memory reserved for setup_selectors
+off:   dd 0
+segm:  dw 0
+; memory reserved for set_gdt
+lim:   dw 0
+addr:  dd 0
+
+       section .text
+; setup_selectors(uint16_t code, uint16_t data)
+; loads the requested selectors to all the selector registers
+       global setup_selectors
+setup_selectors:
+       ; set data selectors directly
+       mov eax, [esp + 8]
+       mov ss, ax
+       mov es, ax
+       mov ds, ax
+       mov gs, ax
+       ;mov fs, ax     ; XXX don't touch fs, we use it to store initial seg
+       ; set cs using a long jump
+       mov eax, [esp + 4]
+       mov [segm], ax
+       mov dword [off], .ldcs
+       jmp [off]
+.ldcs: ret
+
+; set_gdt(uint32_t addr, uint16_t limit)
+; loads the GDTR with the new address and limit for the GDT
+       global set_gdt
+set_gdt:
+       mov eax, [esp + 4]
+       mov [addr], eax
+       mov ax, [esp + 8]
+       mov [lim], ax
+       lgdt [lim]
+       ret
+
+; set_task_reg(uint16_t tss_selector)
+; loads the TSS selector in the task register
+       global set_task_reg
+set_task_reg:
+       mov eax, [esp + 4]
+       ltr [esp + 4]
+       ret
+
+; vi:set ts=8 sts=8 sw=8 ft=nasm: