From d8a61fe84d4b71c21c4ce18a9b7bc78000db725a Mon Sep 17 00:00:00 2001
From: Jonas Hvid <mail@johv.dk>
Date: Sun, 4 Oct 2020 02:02:42 +0200
Subject: [PATCH] Clean up OS interface

We got rid of those weird macros that would try to preserve a bunch of registers
for no reason. The OS interface was changes slightly to allow for simpler
implementation and usage.
---
 impl.asm    |  5 ++--
 main.asm    | 75 +++++++----------------------------------------------
 os/uefi.asm | 11 ++++----
 3 files changed, 18 insertions(+), 73 deletions(-)

diff --git a/impl.asm b/impl.asm
index e8cd883..dd7fc9d 100644
--- a/impl.asm
+++ b/impl.asm
@@ -8,7 +8,7 @@ macro printlen msg, len {
 
   mov rcx, msg
   mov rdx, len
-  sys_print_string
+  call os_print_string
 
   sub rsp, 8
   pop rsi
@@ -183,7 +183,8 @@ parse_number:
   pop rdi
   printlen rdi, [.length]
   newline
-  sys_terminate 100
+  mov rax, 100
+  call os_terminate
 
 section '.data' readable writable
 
diff --git a/main.asm b/main.asm
index 5985b99..407d3a3 100644
--- a/main.asm
+++ b/main.asm
@@ -15,62 +15,12 @@
 ;;
 ;; os_read_char
 ;;   Wait for the user to type a key, and then put the corresponding ASCII byte
-;;   into the buffer pointed to by RCX.
+;;   into RAX.
 ;;
 ;; os_terminate
-;;   Shut down the system.
+;;   Shut down the system, returning the error code given in RAX.
 include '%OS_INCLUDE%'
 
-;; Print a string of a given length.
-;;
-;; Input:
-;; - RCX = Pointer to buffer
-;; - RDX = Buffer length
-;;
-;; Clobbers: RAX, RCX, R11, RDI, RSI
-macro sys_print_string {
-  push r8
-  push r9
-  push r10
-
-  call os_print_string
-
-  pop r10
-  pop r9
-  pop r8
-}
-
-;; Read a character from the user into the given buffer.
-;;
-;; Input:
-;; - RSI = Character buffer
-;;
-;; Output:
-;; - BYTE [RSI] = Character
-;;
-;; Clobbers: RAX, RCX, R11, RDI, RSI, RDX
-macro sys_read_char {
-  push rbx
-  push r8
-  push r9
-  push r10
-  push r15
-
-  mov rcx, rsi
-  call os_read_char
-
-  pop r15
-  pop r10
-  pop r9
-  pop r8
-  pop rbx
-}
-
-macro sys_terminate code {
-  mov rax, code
-  call os_terminate
-}
-
 ;; The code in this macro is placed at the end of each Forth word. When we are
 ;; executing a definition, this code is what causes execution to resume at the
 ;; next word in that definition.
@@ -240,7 +190,7 @@ forth_asm EMIT, 'EMIT'
 
   lea rcx, [rsp]
   mov rdx, 1
-  sys_print_string
+  call os_print_string
 
   add rsp, 8
   popr rax
@@ -265,12 +215,7 @@ forth_asm KEY, 'KEY'
   jne .from_buffer
 
   ;; Reading user input
-  push rsi
-  mov rsi, .buffer
-  sys_read_char
-  pop rsi
-
-  movzx rax, byte [.buffer]
+  call os_read_char
   ret
 
 .from_buffer:
@@ -341,7 +286,7 @@ forth_asm TELL, 'TELL'
 
   pop rdx ; Length
   pop rcx ; Buffer
-  sys_print_string
+  call os_print_string
 
   popr rsi
   popr rax
@@ -349,7 +294,8 @@ forth_asm TELL, 'TELL'
 
 ;; Exit the program cleanly.
 forth_asm TERMINATE, 'TERMINATE'
-  sys_terminate 0
+  mov rax, 0
+  call os_terminate
 
 ;; Duplicate a pair of elements.
 forth_asm PAIRDUP, '2DUP'
@@ -438,7 +384,7 @@ forth_asm DOTU, '.U'
   ;; Print the buffer
   mov rcx, .buffer
   mov rdx, [.printed_length]
-  sys_print_string
+  call os_print_string
 
   ;; Restore RSI and continue execution
   pop rsi
@@ -511,10 +457,7 @@ forth_asm READ_STRING, 'S"'
   mov [.length], 0
 
 .read_char:
-  mov rsi, .char_buffer
-  sys_read_char
-
-  mov al, [.char_buffer]
+  call os_read_char
   cmp al, '"'
   je .done
 
diff --git a/os/uefi.asm b/os/uefi.asm
index 4f8ce56..16fc85d 100644
--- a/os/uefi.asm
+++ b/os/uefi.asm
@@ -129,7 +129,6 @@ os_print_string:
   ret
 
 os_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
@@ -143,19 +142,21 @@ os_read_char:
   cmp rax, r8
   je .read_key
 
-  mov ax, [input_key.UnicodeChar]
-  mov [r15], al
+  movzx rax, word [input_key.UnicodeChar]
 
   ;; Special handling of enter (UEFI gives us '\r', but we want '\n'.)
   cmp ax, $D
   jne .no_enter
-  mov byte [r15], $A
+  mov al, $A
 .no_enter:
 
+  push rax
   ;; Print the character
-  mov rcx, r15
+  mov [char_buffer], al
+  mov rcx, char_buffer
   mov rdx, 1
   call os_print_string
+  pop rax
 
   ret
 
-- 
2.39.2