Start integrating first-stage executable into bootloader

Author: phil-opp

Cargo.lock

@@ -10,6 +10,7 @@ edition = "2021"
 [workspace]
 members = [
     "api",
+    "bios/first_stage",
     "tests/runner",
     "tests/test_kernels/default_settings",
     "tests/test_kernels/map_phys_mem",
@@ -103,6 +104,15 @@ lto = false
 debug = true
 overflow-checks = true
 
+[profile.first-stage]
+inherits = "release"
+opt-level = "s"
+lto = true
+codegen-units = 1
+debug = false
+overflow-checks = false
+
+
 [package.metadata.docs.rs]
 default-target = "x86_64-unknown-linux-gnu"
 

Cargo.toml

@@ -1,16 +1,9 @@
 [package]
-name = "first_stage"
+name = "bootloader_first_stage"
 version = "0.1.0"
 authors = ["Philipp Oppermann <dev@phil-opp.com>"]
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-
-[profile.release]
-opt-level = "s"
-lto = true
-codegen-units = 1
-
-# debug = true

real_mode/first_stage/.gitignore renamed to bios/first_stage/.gitignore

@@ -0,0 +1,110 @@
+.section .boot, "awx"
+.global _start
+.code16
+
+# This stage initializes the stack, enables the A20 line
+
+_start:
+    # zero segment registers
+    xor ax, ax
+    mov ds, ax
+    mov es, ax
+    mov ss, ax
+    mov fs, ax
+    mov gs, ax
+
+    # clear the direction flag (e.g. go forward in memory when using
+    # instructions like lodsb)
+    cld
+
+    # initialize stack
+    mov sp, 0x7c00
+
+enable_a20:
+    # enable A20-Line via IO-Port 92, might not work on all motherboards
+    in al, 0x92
+    test al, 2
+    jnz enable_a20_after
+    or al, 2
+    and al, 0xFE
+    out 0x92, al
+enable_a20_after:
+
+enter_protected_mode:
+    # clear interrupts
+    cli
+    push ds
+    push es
+
+    lgdt [gdt32info]
+
+    mov eax, cr0
+    or al, 1    # set protected mode bit
+    mov cr0, eax
+
+    jmp protected_mode                # tell 386/486 to not crash
+
+protected_mode:
+    mov bx, 0x10
+    mov ds, bx # set data segment
+    mov es, bx # set extra segment
+
+    and al, 0xfe    # clear protected mode bit
+    mov cr0, eax
+
+unreal_mode:
+    pop es # get back old extra segment
+    pop ds # get back old data segment
+    sti
+
+    # back to real mode, but internal data segment register is still loaded
+    # with gdt segment -> we can access the full 4GiB of memory
+
+    mov bx, 0x0f02         # attrib/char of smiley
+    mov eax, 0xb8f00       # note 32 bit offset
+    mov word ptr ds:[eax], bx
+
+check_int13h_extensions:
+    push 'y'    # error code
+    mov ah, 0x41
+    mov bx, 0x55aa
+    # dl contains drive number
+    int 0x13
+    jc fail
+    pop ax      # pop error code again
+
+rust:
+    # push arguments
+    push dx     # disk number
+    call first_stage
+
+spin:
+    hlt
+    jmp spin
+
+gdt32info:
+   .word gdt32_end - gdt32 - 1  # last byte in table
+   .word gdt32                  # start of table
+
+gdt32:
+    # entry 0 is always unused
+    .quad 0
+codedesc:
+    .byte 0xff
+    .byte 0xff
+    .byte 0
+    .byte 0
+    .byte 0
+    .byte 0x9a
+    .byte 0xcf
+    .byte 0
+datadesc:
+    .byte 0xff
+    .byte 0xff
+    .byte 0
+    .byte 0
+    .byte 0
+    .byte 0x92
+    .byte 0xcf
+    .byte 0
+gdt32_end:

real_mode/first_stage/16-bit-linker.ld renamed to bios/first_stage/16-bit-linker.ld

@@ -19,7 +19,7 @@
 	"relocation-model": "static",
 	"pre-link-args": {
 		"ld.lld": [
-			"--script=16-bit-linker.ld"
+			"--script=bios/first_stage/16-bit-linker.ld"
 		]
 	}
 }