add comments to args passed to vbr

Makefile

@@ -108,7 +108,7 @@ imgz: $(IMGZ)
 # Helpers
 
 run: $(IMG)
-	@$(QEMU) $(QEMU_OPTS) -drive file=$(IMG),if=ide,index=0,media=disk,format=raw \
+	@$(QEMU) $(QEMU_ARGS) -drive file=$(IMG),if=ide,index=0,media=disk,format=raw \
 
 run_bochs: $(IMG)
 	@bochs -q

README.md

@@ -1,6 +1,8 @@
 # Stevia Bootloader
 
-Stevia is a lightweight, hobby bootloader written in Assembly and C, designed for educational purposes. It targets 686+ and aims to be simple, approachable, and understandable, focusing on minimalism and core functionality.
+Stevia is a lightweight, hobby bootloader written in Assembly (NASM) and is designed for educational purposes. It targets 686+ and aims to be simple, approachable, and understandable, focusing on minimalism and core functionality.
+
+Please note: **Most development currently takes place in Bochs (and maybe is tested on QEMU), due to this, the code in this repo has not been tested throughly aginist real hardware. As with most projects of this nature, there is a risk of damage due to improper programing of hardware, while careful effort is taken to not break the computer...accidents and mistakes can/do happen.**
 
 ## Features
 
@@ -56,6 +58,8 @@ To build and run Stevia, you will need the following tools installed on your sys
 
 Stevia is intended to be a learning tool for those interested in low-level programming, focusing on understanding the basics of how a computer starts up and manages early system resources.
 
+You are welcome to fork/review the code base but I am generally not accepting PR's/Contributions to the code at this time.
+
 ## License
 
 This project is licensed under the GPLv3 License. See the [LICENSE](LICENSE.md) or [COPYING](COPYING) file for more details.

include/cdecl16.inc

@@ -42,6 +42,7 @@
 ; __CDECL16_PROC_ARGS nargs
 ;   Creates %$arg1 .. %$argN as [bp+4], [bp+6], ...
 ;   for use inside of function bodies
+; BUG: still needs to be tested
 %ifnmacro __CDECL16_PROC_ARGS
 %macro __CDECL16_PROC_ARGS 1
     %push __CDECL16_PROC_ARGS
@@ -78,6 +79,7 @@
 ; __CDECL16_CALL_ARGS_SIZED func, size1[, size2 ...]  ; sizes in BYTES
 ;   if you *need* to pass dword sized args in 16-bit mode, use this to properly
 ;   count the stack frame to restore later!
+; BUG: still needs to be tested
 %ifnmacro __CDECL16_CALL_ARGS_SIZED
 %macro __CDECL16_CALL_ARGS_SIZED 2-*
     %push __CDECL16_CALL_ARGS_SIZED
@@ -124,13 +126,21 @@
 %endmacro
 %endif
 
+;
+; Only setup the minimum stack frame
+; unlike the above, everything is caller save
+;
 %ifnmacro __FASTCALL16_ENTRY
-%macro __FASTCALL16_ENTRY 0
+%macro __FASTCALL16_ENTRY 0-1
     push bp
     mov bp, sp
+    %if %0 = 1
+    sub  sp, %1        ; reserve locals only when needed
+    %endif
 %endmacro
 %endif
 
+; restore minimum stack frame, all regs are caller save
 %ifnmacro __FASTCALL16_EXIT
 %macro __FASTCALL16_EXIT 0
     mov sp, bp

src/mbr/mbr.nasm

@@ -146,9 +146,9 @@ main:
         call kmemcpy                            ; copy partition table to bss
         add sp, 0x6
         
-        mov si, word [bp - 4]
+        mov si, word [bp - 4]                   ; partition_offset address
-        mov dl, byte [bp - 2]
+        mov dl, byte [bp - 2]                   ; pass drive # from BIOS to VBR in dl
-        mov bx, partition_table
+        mov bx, partition_table                 ; partition_table address
         jmp word 0x0000:VBR_ENTRY
 
 ; ###############