-;; vim: syntax=fasm
-
-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
-
-;; Based on https://wiki.osdev.org/Uefi.inc
-macro struct name {
- virtual at 0
- name name
- end virtual
-}
-
-struc EFI_TABLE_HEADER {
- dq ?
- dd ?
- dd ?
- dd ?
- dd ?
-}
-
-struc EFI_SYSTEM_TABLE {
- .Hdr EFI_TABLE_HEADER
- .FirmwareVendor dq ? ; CHAR16*
- .FirmwareRevision dd ? ; UINT32
- align 8
- .ConsoleInHandle dq ? ; EFI_HANDLE
- .ConIn dq ? ; EFI_SIMPLE_TEXT_INPUT_PROTOCOL*
- .ConsoleOutHandle dq ? ; EFI_HANDLE
- .ConOut dq ? ; EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL*
- ; ...
-}
-struct EFI_SYSTEM_TABLE
-
-struc EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL {
- .Reset dq ? ; EFI_TEXT_RESET
- .OutputString dq ? ; EFI_TEXT_STRING
- ; ...
-}
-struct EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL
-
-struc EFI_SIMPLE_TEXT_INPUT_PROTOCOL {
- .Reset dq ? ; EFI_INPUT_RESET
- .ReadKeyStroke dq ? ; EFI_INPUT_READ_KEY
- ; ...
-}
-struct EFI_SIMPLE_TEXT_INPUT_PROTOCOL
-
-struc EFI_INPUT_KEY {
- .ScanCode dw ? ; UINT16
- .UnicodeChar dw ? ; CHAR16
- align 8
-}
-struct EFI_INPUT_KEY
-
-;; }}}
-
-section '.text' code executable readable
-
-main:
- ; 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:
- mov r8, rcx
- mov r9, rdx
-
- mov r10, r9
- add r10, r10
-
- ; We take an input string of bytes without any terminator. We need to turn
- ; this string into a string of words, terminated by a null character.
- mov rcx, 0
- mov rsi, 0
-.copy_byte:
- cmp rcx, r10
- je .done
-
- mov al, byte [r8 + rsi]
- lea rdx, [.output_buffer + rcx]
- mov byte [rdx], al
- inc rcx
- inc rsi
-
- lea rdx, [.output_buffer + rcx]
- mov byte [rdx], 0
- inc rcx
-
- jmp .copy_byte
-.done:
- lea rdx, [.output_buffer + r10]
- mov byte [rdx], 0
-
- ; At this point we have our null-terminated word-string at .output_buffer. Now
- ; we just need to print it.
-
- mov rcx, [system_table] ; EFI_SYSTEM_TABLE* rcx
- mov rcx, [rcx + EFI_SYSTEM_TABLE.ConOut] ; EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL* rcx
- mov rdx, .output_buffer
- mov rbx, [rcx + EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.OutputString] ; EFI_TEXT_STRING rbx
- sub rsp, 32
- call rbx
- add rsp, 32
- ret
-
-;; Read a character as an ASCII byte into the given buffer.
-;;
-;; Inputs:
-;; - RCX = Character buffer (1 byte)
-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 rbx, [rcx + EFI_SIMPLE_TEXT_INPUT_PROTOCOL.ReadKeyStroke] ; EFI_INPUT_READ_KEY rbx
- mov rdx, input_key ; EFI_INPUT_KEY* rdx
- sub rsp, 32
- call rbx
- add rsp, 32
-
- mov r8, EFI_NOT_READY
- cmp rax, r8
- je .read_key
-
- mov ax, [input_key.UnicodeChar]
- mov [r15], al
-
- ret
-
-section '.data' readable writable
-
-system_table dq ? ; EFI_SYSTEM_TABLE*
-
-hello_string db 'Hello, world!', 0xD, 0xA, 'Here is some more text.', 0xD, 0xA
-.len = $ - hello_string
-
-print_string.output_buffer rq 0x400
-
-char_buffer db ?
-
-input_key EFI_INPUT_KEY