From: Duje Mihanović <duje.mihanovic@skole.hr>
Date: Mon, 27 Jun 2022 19:29:50 +0000 (+0200)
Subject: Merge branch 'elf' into mm
X-Git-Url: http://git.dujemihanovic.xyz/%7B%7B%20%24.Site.BaseURL%20%7D%7Dposts/index.xml?a=commitdiff_plain;h=5eb69417259dd239d1d7b69724b7e2bccb7d146e;hp=da4e7bf5dd2b9448b638255a20ee503b0641e495;p=nameless-os.git

Merge branch 'elf' into mm
---

diff --git a/boot/x86/stage3/loader.s b/boot/x86/stage3/loader.s
index 87598f4..bd2fb9b 100644
--- a/boot/x86/stage3/loader.s
+++ b/boot/x86/stage3/loader.s
@@ -210,3 +210,5 @@ ss_s: db "SS: ", 0
 space: db " ", 0
 hex_delm: db "0x", 0
 newline: db 0xd, 0xa, 0
+
+%include "paging.s"
diff --git a/boot/x86/stage3/paging.s b/boot/x86/stage3/paging.s
new file mode 100644
index 0000000..004da84
--- /dev/null
+++ b/boot/x86/stage3/paging.s
@@ -0,0 +1,80 @@
+; Code for enabling paging before calling the kernel
+; Identity maps the VGA framebuffer memory and high-half maps the kernel memory
+bits 32
+
+section .text
+
+; The problem with this code is that it assumes that the kernel's various
+; sections occupy a certain number of pages. As of writing it is correct, but as
+; the kernel grows this code may fail to map those pages, which is not good. The
+; solution to this is to use ELF instead of a flat binary. This was not done
+; before because it would require paging, but now that paging works using ELF is
+; a possibility which must be exploited.
+
+enable_paging:
+	push eax
+	mov eax, cr0
+	or eax, 0x80000000
+	mov cr0, eax
+	pop eax
+	ret
+
+load_paging_structs:
+	push eax
+	push ebx
+	xor ebx, ebx
+.pt_low_loop:
+	mov eax, ebx
+	shl eax, 12
+	or eax, 1|2 ; P and R/W flags
+	mov [page_table_low+ebx*4], eax
+	inc ebx
+	cmp ebx, 0x100
+	jl .pt_low_loop
+
+	xor ebx, ebx
+.pt_high_ro_loop:
+	mov eax, ebx
+	add eax, 0x100
+	shl eax, 12
+	or eax, 1 ; P flag
+	mov [page_table_high+ebx*4], eax
+	inc ebx
+	cmp ebx, 0x2
+	jl .pt_high_ro_loop
+
+	mov ebx, 0x2
+.pt_high_rw_loop:
+	mov eax, ebx
+	add eax, 0x100
+	shl eax, 12
+	or eax, 1|2 ; P and R/W flags
+	mov [page_table_high+ebx*4], eax
+	inc ebx
+	cmp ebx, 0x9
+	jl .pt_high_rw_loop
+
+	mov eax, page_table_low
+	and eax, 0xfffff000
+	or eax, 1|2
+	mov [page_directory], eax
+
+	mov eax, page_table_high
+	and eax, 0xfffff000
+	or eax, 1|2
+	mov [page_directory+768*4], eax
+
+	mov eax, page_directory
+	mov cr3, eax
+	pop ebx
+	pop eax
+	ret
+
+section .data
+align 4096
+page_table_low:
+	times 1024 dd 0
+page_table_high:
+	times 1024 dd 0
+page_directory:
+	times 1024 dd 0
diff --git a/include/arch/x86/mm/paging.h b/include/arch/x86/mm/paging.h
new file mode 100644
index 0000000..a4bdf22
--- /dev/null
+++ b/include/arch/x86/mm/paging.h
@@ -0,0 +1,35 @@
+#ifndef X86_PAGING_H
+#define X86_PAGING_H
+
+struct page_directory_entry {
+	unsigned p: 1,
+		 rw: 1,
+		 us: 1,
+		 pwt: 1,
+		 pcd: 1,
+		 a: 1,
+		 ignored: 1,
+		 ps: 1,
+		 ignored2: 4,
+		 page_table_addr: 20;
+} __attribute__((packed));
+
+struct page_table_entry {
+	unsigned p: 1,
+		 rw: 1,
+		 us: 1,
+		 pwt: 1,
+		 pcd: 1,
+		 a: 1,
+		 d: 1,
+		 pat: 1,
+		 g: 1,
+		 ignored: 3,
+		 page_frame_addr: 20;
+} __attribute__((packed));
+
+struct pf_errcode {
+	unsigned p: 1, wr: 1, us: 1, rsvd: 1, id: 1, pk: 1, ss: 1, hlat: 1, reserved: 7, sgx: 1, reserved2: 15;
+} __attribute__((packed));
+
+#endif