Make it run on UEFI!

The program is now usable, albeit barely, running inside QEMU, with the only
dependency being UEFI! Very cool!

Right now, no output is printed to the screen when you type characters, newlines
aren't printed correctly, and the program doesn't accept Enter as valid
whitespace when reading input.

.gitignore

@@ -1 +1,3 @@
-/main
+/out
+/OVMF_CODE.fd
+/OVMF_VARS.fd

Makefile

@@ -1,10 +1,23 @@
-.PHONY: run
-run: main
-	cat sys.f - | ./main
+.PHONY: qemu
+qemu: out/main OVMF_CODE.fd OVMF_VARS.fd
+	# Based on https://wiki.osdev.org/UEFI#Emulation_with_QEMU_and_OVMF
+	qemu-system-x86_64 -cpu qemu64 \
+		-drive if=pflash,format=raw,unit=0,file=OVMF_CODE.fd,readonly=on \
+		-drive if=pflash,format=raw,unit=1,file=OVMF_VARS.fd \
+		-net none \
+		-drive format=raw,file=fat:rw:out \
+		-display type=gtk,zoom-to-fit=on
 
-main: main.asm impl.asm bootstrap.asm sys.f
-	fasm $< $@
+# Assuming 'ovmf' package on Arch Linux is installed.
+OVMF_CODE.fd: /usr/share/ovmf/x64/OVMF_CODE.fd
+	cp $< $@
+OVMF_VARS.fd: /usr/share/ovmf/x64/OVMF_VARS.fd
+	cp $< $@
+
+out/main: main.asm impl.asm bootstrap.asm sys.f uefi.asm
+	mkdir -p out
+	fasm $< out/main
 
 .PHONY: clean
 clean:
-	rm -f main
+	rm -rf out OVMF_CODE.fd OVMF_VARS.fd

impl.asm

@@ -1,6 +1,6 @@
 ;; vim: syntax=fasm
 
-segment readable executable
+section '.text' code readable executable
 
 macro printlen msg, len {
   push rsi
@@ -231,7 +231,7 @@ parse_number:
   newline
   sys_terminate 100
 
-segment readable writable
+section '.data' readable writable
 
 find.search_length dq ?
 find.search_buffer dq ?

main.asm

@@ -1,6 +1,6 @@
 ;; vim: syntax=fasm
 
-format ELF64 executable
+include "uefi.asm"
 
 ;; "Syscalls" {{{
 
@@ -22,10 +22,15 @@ format ELF64 executable
 ;;
 ;; Clobbers: RAX, RCX, R11, RDI, RSI
 macro sys_print_string {
-  mov rax, 1
-  mov rdi, 1
-  mov rsi, rcx
-  syscall
+  push r8
+  push r9
+  push r10
+
+  call uefi_print_string
+
+  pop r10
+  pop r9
+  pop r8
 }
 
 ;; Read a character from the user into the given buffer.
@@ -38,16 +43,25 @@ macro sys_print_string {
 ;;
 ;; Clobbers: RAX, RCX, R11, RDI, RSI, RDX
 macro sys_read_char {
-  mov rax, 0
-  mov rdi, 0
-  mov rdx, 1
-  syscall
+  push rbx
+  push r8
+  push r9
+  push r10
+  push r15
+
+  mov rcx, rsi
+  call uefi_read_char
+
+  pop r15
+  pop r10
+  pop r9
+  pop r8
+  pop rbx
 }
 
 macro sys_terminate code {
-  mov rax, $3C
-  mov rdi, code
-  syscall
+  mov rax, code
+  call uefi_terminate
 }
 
 ;; }}}
@@ -109,9 +123,7 @@ macro forth_asm label, name, immediate {
 .start:
 }
 
-segment readable executable
-
-entry main
+section '.text' code readable executable
 
 include "impl.asm"      ; Misc. subroutines
 include "bootstrap.asm" ; Forth words encoded in Assembly
@@ -120,6 +132,8 @@ main:
   cld                        ; Clear direction flag so LODSQ does the right thing.
   mov rbp, return_stack_top  ; Initialize return stack
 
+  call uefi_initialize
+
   mov rax, MAIN
   jmp qword [rax]
 
@@ -597,7 +611,7 @@ forth INPUT_LENGTH, 'INPUT-LENGTH'
   dq LIT, input_buffer_length
   dq EXIT
 
-segment readable writable
+section '.data' readable writable
 
 ;; The LATEST variable holds a pointer to the word that was last added to the
 ;; dictionary. This pointer is updated as new words are added, and its value is
@@ -637,8 +651,6 @@ here_top rq $4000
 rq $2000
 return_stack_top:
 
-segment readable
-
 ;; We store some Forth code in sys.f that defined common words that the user
 ;; would expect to have available at startup. To execute these words, we just
 ;; include the file directly in the binary, and then interpret it at startup.

uefi/main.asm → uefi.asm

@@ -3,20 +3,6 @@
 format pe64 dll efi
 entry main
 
-;; [TODO] We need to provide the following:
-;; - [X] Print a string of a given length
-;; - [ ] Print a single character
-;; - [ ] Terminate the program (? - What should this do?)
-;; - [X] Read a single character
-;;       - This should allow the user to type in a string, and then feed the
-;;         buffer to us one character at a time.
-;;       - [ ] We want to show the user's input on the screen while reading
-;; - [ ] Read a file that was bundled with the program
-;;       - It looks like we can use EFI_LOAD_FILE_PROTOCOL.LoadFile() to load
-;;         a file into a buffer. In order to be able to use this, we need to
-;;         have some way of interpreting a static buffer instead of reading as
-;;         we go.
-
 ;; EFI struct definitions {{{
 
 EFI_NOT_READY = 0x8000_0000_0000_0000 or 6
@@ -74,33 +60,19 @@ struct EFI_INPUT_KEY
 
 section '.text' code executable readable
 
-main:
+uefi_initialize:
   ; At program startup, RDX contains an EFI_SYSTEM_TABLE*.
   mov [system_table], rdx
-
-  mov rcx, hello_string
-  mov rdx, hello_string.len
-  call print_string
-
-  mov rcx, char_buffer
-  call read_char
-
-  mov rcx, char_buffer
-  mov rdx, 1
-  call print_string
-
-  mov rcx, hello_string
-  mov rdx, hello_string.len
-  call print_string
-
   ret
 
 ;; Print a string of the given length.
 ;;
 ;; Inputs:
 ;;  - RCX = String buffer
 ;;  - RDX = String length
-print_string:
+;;
+;; [TODO] Handle newlines correctly. (I.e. translate '\n' to '\r\n'.)
+uefi_print_string:
   mov r8, rcx
   mov r9, rdx
 
@@ -146,13 +118,16 @@ print_string:
 ;;
 ;; Inputs:
 ;; - RCX = Character buffer (1 byte)
-read_char:
+;;
+;; [TODO] Show the user's input on screen while they are typing.
+;; [TODO] Handle enter key correctly (should return '\n').
+uefi_read_char:
   mov r15, rcx
 .read_key:
-  mov rcx, [system_table] ; EFI_SYSTEM_TABLE* rcx
-  mov rcx, [rcx + EFI_SYSTEM_TABLE.ConIn] ; EFI_SIMPLE_TEXT_INPUT_PROTOCOL* rcx
+  mov rcx, [system_table]                                       ; EFI_SYSTEM_TABLE* rcx
+  mov rcx, [rcx + EFI_SYSTEM_TABLE.ConIn]                       ; EFI_SIMPLE_TEXT_INPUT_PROTOCOL* rcx
   mov rbx, [rcx + EFI_SIMPLE_TEXT_INPUT_PROTOCOL.ReadKeyStroke] ; EFI_INPUT_READ_KEY rbx
-  mov rdx, input_key ; EFI_INPUT_KEY* rdx
+  mov rdx, input_key                                            ; EFI_INPUT_KEY* rdx
   sub rsp, 32
   call rbx
   add rsp, 32
@@ -166,14 +141,24 @@ read_char:
 
   ret
 
+;; Terminate with the given error code.
+;;
+;; Inputs:
+;; - RCX = Error code
+uefi_terminate:
+  mov rcx, terminated_msg
+  mov rdx, terminated_msg.len
+  call uefi_print_string
+  jmp $
+
 section '.data' readable writable
 
-system_table dq ?  ; EFI_SYSTEM_TABLE*
+system_table dq ? ; EFI_SYSTEM_TABLE*
 
-hello_string db 'Hello, world!', 0xD, 0xA, 'Here is some more text.', 0xD, 0xA
-.len = $ - hello_string
+terminated_msg db 0xD, 0xA, '(The program has terminated.)', 0xD, 0xA
+.len = $ - terminated_msg
 
-print_string.output_buffer rq 0x400
+uefi_print_string.output_buffer rq 0x400
 
 char_buffer db ?