From 1ce7df083a8b1b6d3ed63e529d128e399f5ee032 Mon Sep 17 00:00:00 2001
From: nakst <>
Date: Fri, 29 Oct 2021 14:42:47 +0100
Subject: [PATCH] booting into 32 bit kernels
---
arch/x86_64/kernel.cpp | 1 +
boot/x86/loader.s | 179 ++++++++++++++++++++++++++++++++++++++++-
util/build.c | 10 ++-
3 files changed, 186 insertions(+), 4 deletions(-)
diff --git a/arch/x86_64/kernel.cpp b/arch/x86_64/kernel.cpp
index 98eabeb..73448e5 100644
--- a/arch/x86_64/kernel.cpp
+++ b/arch/x86_64/kernel.cpp
@@ -303,6 +303,7 @@ bool MMArchMapPage(MMSpace *space, uintptr_t physicalAddress, uintptr_t virtualA
// That said, a CPU won't overwrite and clear a dirty bit when writing out its accessed flag (tested on Qemu);
// see here https://stackoverflow.com/questions/69024372/.
// Tl;dr: if a CPU ever sees an entry without these bits set, it can overwrite the entry with junk whenever it feels like it.
+ // TODO Should we be marking page tables as dirty/accessed? (Including those made by the 32-bit AND 64-bit bootloader and MMArchInitialise).
value |= (1 << 5) | (1 << 6);
if ((oldValue & 1) && !(flags & MM_MAP_PAGE_OVERWRITE)) {
diff --git a/boot/x86/loader.s b/boot/x86/loader.s
index bf4314d..b5c95f2 100644
--- a/boot/x86/loader.s
+++ b/boot/x86/loader.s
@@ -1,7 +1,7 @@
[bits 16]
[org 0x1000]
-; This is missing any fileSystem specific macros.
+; This is missing any file system specific macros.
%define vesa_info 0x7000
%define os_installation_identifier 0x7FF0
%define temporary_load_buffer 0x9000
@@ -363,7 +363,184 @@ setup_elf:
jne error_32
cmp byte [ebx + 4],2
je setup_elf_64
+ cmp byte [ebx + 4],1
jne error_32
+ jmp setup_elf_32
+
+setup_elf_32:
+ mov dword [page_table_allocation_location],0x2000
+
+ ; Check the ELF data is correct
+ mov ebx,[kernel_buffer]
+ mov esi,error_bad_kernel
+ cmp byte [ebx + 5],1
+ jne error_32
+ cmp byte [ebx + 7],0
+ jne error_32
+ cmp byte [ebx + 16],2
+ jne error_32
+ cmp byte [ebx + 18],0x03
+ jne error_32
+
+ ; Find the program headers
+ ; EAX = ELF header, EBX = program headers
+ mov eax,ebx
+ mov ebx,[eax + 28]
+ add ebx,eax
+
+ ; ECX = entries, EDX = size of entry
+ movzx ecx,word [eax + 44]
+ movzx edx,word [eax + 42]
+
+ ; Loop through each program header
+ .loop_program_headers:
+ push eax
+ push ecx
+ push edx
+ push ebx
+
+ ; Only deal with load segments
+ mov eax,[ebx]
+ cmp eax,1
+ jne .next_entry
+
+ ; Work out how many physical pages we need to allocate
+ mov ecx,[ebx + 20]
+ shr ecx,12
+ inc ecx
+
+ ; Get the starting virtual address
+ mov eax,[ebx + 8]
+ mov [.target_page],eax
+
+ ; For every frame in the segment
+ .frame_loop:
+ xor ebx,ebx
+
+ ; For every memory region
+ .memory_region_loop:
+
+ ; Check the region has enough pages remaining
+ mov eax,[ebx + memory_map + 8]
+ or eax,eax
+ jz .try_next_memory_region
+
+ ; Remove one page from the region
+ mov eax,[ebx + memory_map + 4]
+ or eax,eax
+ jnz .try_next_memory_region ; Reject 64-bit pages.
+ mov eax,[ebx + memory_map + 0]
+ mov [.physical_page],eax
+ add eax,0x1000
+ mov [ebx + memory_map + 0],eax
+ sub dword [ebx + memory_map + 8],1
+
+ jmp .found_physical_page
+
+ ; Go to the next memory region
+ .try_next_memory_region:
+ add ebx,16
+ mov eax,[load_memory_map.pointer]
+ cmp ebx,eax
+ jne .memory_region_loop
+ mov esi,error_no_memory
+ jmp error_32
+
+ ; Map the page into virtual memory
+ .found_physical_page:
+
+ ; Make sure we have a page table
+ mov eax,[.target_page]
+ shr eax,22
+ shl eax,2
+ add eax,0xFFFFF000
+ mov ebx,[eax]
+ cmp ebx,0
+ jne .has_pt
+ mov ebx,[page_table_allocation_location]
+ add ebx,page_directory
+ or ebx,7
+ mov [eax],ebx
+ add dword [page_table_allocation_location],0x1000
+ mov eax,cr3
+ mov cr3,eax
+ .has_pt:
+
+ ; Map the page!
+ mov eax,[.target_page]
+ shr eax,12
+ mov ebx,[.physical_page]
+ or ebx,0x103
+ shl eax,2
+ add eax,0xFFC00000
+ mov [eax],ebx
+ mov ebx,[.target_page]
+ invlpg [ebx]
+
+ ; Go to the next frame
+ add dword [.target_page],0x1000
+ dec ecx
+ or ecx,ecx
+ jnz .frame_loop
+
+ ; Restore the pointer to the segment
+ pop ebx
+ push ebx
+
+ ; Clear the memory
+ mov ecx,[ebx + 20]
+ xor eax,eax
+ mov edi,[ebx + 8]
+ rep stosb
+
+ ; Copy the memory
+ mov ecx,[ebx + 16]
+ mov esi,[ebx + 4]
+ add esi,[kernel_buffer]
+ mov edi,[ebx + 8]
+ rep movsb
+
+ ; Go to the next entry
+ .next_entry:
+ pop ebx
+ pop edx
+ pop ecx
+ pop eax
+
+ add ebx,edx
+ dec ecx
+ or ecx,ecx
+ jnz .loop_program_headers
+
+ jmp run_kernel32
+
+ .target_page: dd 0
+ .physical_page: dd 0
+
+run_kernel32:
+ ; Let the kernel use the memory that was used to store the executable
+ xor eax,eax
+ mov ebx,[load_memory_map.pointer]
+ mov [memory_map + ebx + 4],eax
+ mov [memory_map + ebx + 12],eax
+ mov [memory_map + ebx + 16],eax
+ mov [memory_map + ebx + 20],eax
+ mov eax,[memory_map + ebx + 8]
+ mov [memory_map + ebx + 24],eax
+ mov eax,[memory_map + ebx + 12]
+ mov [memory_map + ebx + 28],eax
+ mov eax,[kernel_buffer]
+ mov [memory_map + ebx],eax
+ mov eax,[kernel_size]
+ shr eax,12
+ mov [memory_map + ebx + 8],eax
+
+ ; Execute the kernel's _start function
+ mov ebx,[kernel_buffer]
+ mov ecx,[ebx + 24]
+ xor edi,edi
+ mov esi,1
+ jmp ecx
setup_elf_64:
; Check that the processor is 64-bit
diff --git a/util/build.c b/util/build.c
index 7a486d1..791106a 100644
--- a/util/build.c
+++ b/util/build.c
@@ -2,14 +2,16 @@
#define _GNU_SOURCE
#endif
-#if 1
+#if 0
#define TOOLCHAIN_PREFIX "x86_64-essence"
#define TARGET_NAME "x86_64"
#define TOOLCHAIN_HAS_RED_ZONE
#define TOOLCHAIN_HAS_CSTDLIB
+#define QEMU_EXECUTABLE "qemu-system-x86_64"
#else
#define TOOLCHAIN_PREFIX "i686-elf"
#define TARGET_NAME "x86_32"
+#define QEMU_EXECUTABLE "qemu-system-i386"
#endif
#define WARNING_FLAGS \
@@ -519,7 +521,7 @@ void Run(int emulator, int log, int debug) {
serialFlags[0] = 0;
}
- CallSystemF("%s %s qemu-system-x86_64 %s%s %s -m %d %s -smp cores=%d -cpu Haswell "
+ CallSystemF("%s %s " QEMU_EXECUTABLE " %s%s %s -m %d %s -smp cores=%d -cpu Haswell "
" -device qemu-xhci,id=xhci -device usb-kbd,bus=xhci.0,id=mykeyboard -device usb-mouse,bus=xhci.0,id=mymouse "
" -netdev user,id=u1 -device e1000,netdev=u1 -object filter-dump,id=f1,netdev=u1,file=bin/net.dat "
" %s %s %s %s %s %s %s ",
@@ -1397,7 +1399,9 @@ void DoCommand(const char *l) {
LineCountFile("", "start.sh");
const char *folders[] = {
- "desktop/", "boot/x86/", "drivers/", "kernel/", "apps/", "apps/file_manager/", "shared/", "util/"
+ "desktop/", "boot/x86/", "drivers/", "kernel/",
+ "apps/", "apps/file_manager/", "shared/", "util/",
+ "arch/", "arch/x86_32/", "arch/x86_64/",
};
for (uintptr_t i = 0; i < sizeof(folders) / sizeof(folders[0]); i++) {