From f9c0bd3db6c8053ca474676c8929ed5f50cc2ddd Mon Sep 17 00:00:00 2001
From: Jarkko Toivanen <jt@jakest.us>
Date: Fri, 8 Sep 2023 12:02:02 +0300
Subject: [PATCH] Improved framebuffer compatibility and memory safeguard

---
 src/framebuffer.asm | 25 ++++++++++++++-----------
 src/mbootinfo.asm   |  6 ------
 src/start32.asm     | 11 ++++++-----
 3 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/src/framebuffer.asm b/src/framebuffer.asm
index d831dec..9c215a4 100644
--- a/src/framebuffer.asm
+++ b/src/framebuffer.asm
@@ -10,15 +10,23 @@ putpixel:
 
 	cld
 
+	; check pixel is in screen
+	mov ebx, [ebp+12]	;y
+	cmp ebx, [mbootinfo.fb_height]
+	jge .done
+	mov ecx, [ebp+8]	;x
+	cmp ecx, [mbootinfo.fb_width]
+	jge .done
+
 	; Destination
 	mov edi, [mbootinfo.fb_addr]
 	mov eax, [mbootinfo.fb_pitch]
-	mul dword [ebp+12]   ;y
+	mul dword ebx   ;y
 	add edi, eax
 
-	mov eax, [ebp+8]   ;x
-	movzx ebx, byte [mbootinfo.fb_bytespp]
-	mul ebx
+	mov eax, ecx   ;x
+	movzx ecx, byte [mbootinfo.fb_bytespp]
+	mul ecx
 	add edi, eax
 
 
@@ -26,13 +34,8 @@ putpixel:
 	mov eax, [ebp + 16]
 
 	; Poke videomemory
-	stosb
-	stosb
-	stosb
-
-	cmp [mbootinfo.fb_bpp], 24
-	je .done
-	stosb
+	cld
+	rep stosb
 .done:
 	pop edi
 	pop ecx
diff --git a/src/mbootinfo.asm b/src/mbootinfo.asm
index 1a6f559..2ff07e8 100644
--- a/src/mbootinfo.asm
+++ b/src/mbootinfo.asm
@@ -45,12 +45,6 @@ mbootgetinfo:
 	add esi, 4
 
 	mov al, [esi]
-	cmp al, 32
-	je .bppokay
-	cmp al, 24
-	je .bppokay
-	jmp mbootunsupportedfbbpp
-.bppokay:
 	mov [mbootinfo.fb_bpp], al
 	inc esi
 
diff --git a/src/start32.asm b/src/start32.asm
index fc3ae85..f8e5d36 100644
--- a/src/start32.asm
+++ b/src/start32.asm
@@ -11,8 +11,9 @@ MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST
 MB_HEADER_FLAGS      equ MB_PAGE_ALIGN or MB_MEMORY_INFO or MB_VIDEO_REQUEST or MB_AOUT_KLUDGE
 MB_CHECKSUM          equ -(MB_HEADER_MAGIC + MB_HEADER_FLAGS)
 
-VWIDTH  equ 1024
-VHEIGHT equ 768
+VWIDTH  equ 640
+VHEIGHT equ 480
+VDEPTH  equ 24
 
 multiboot:
 	dd MB_HEADER_MAGIC
@@ -26,7 +27,7 @@ multiboot:
 	dd 0	; video mode_type (0:fb, 1:txt) (set flags[2]!)
 	dd VWIDTH	; video width
 	dd VHEIGHT	; video height
-	dd 24	; video depth
+	dd VDEPTH	; video depth
 
 start:
 	; Setup stack
@@ -103,8 +104,8 @@ start:
 	mov ebx, 767
 	mov ecx, 1023
 	push 0xff
-	push 767
-	push 1023
+	push 479
+	push 639
 	call putpixel
 	add esp, 3*4