commit 9b53b95a1c3b46e5a54734a46f37790460c9265e
author Paolo Bonzini <pbonzini@redhat.com> Mon Dec 29 14:43:42 2014 +0100
committer Paolo Bonzini <pbonzini@redhat.com> Thu Jan 18 10:43:13 2024 +0100
tree 9edfc2fa6e3c0434ac065edae3bc6c56786dffff
parent f9b925fd41337027e959baeb23d714b5214cd5ff

vga: mask addresses in non-VESA modes to 256k

This allows setting the start address to a high value, and reading the
bottom of the screen from the beginning of VRAM.  Commander Keen 4
("Goodbye, Galaxy!") relies on this behavior.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/display/vga-helpers.h

diff --git a/hw/display/vga-helpers.h b/hw/display/vga-helpers.h
index 10e9cfd..83b9a15 100644
--- a/hw/display/vga-helpers.h
+++ b/hw/display/vga-helpers.h
@@ -108,7 +108,7 @@
     plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf];
     width >>= 3;
     for(x = 0; x < width; x++) {
-        data = vga_read_dword_le(vga, addr);
+        data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1));
         data &= plane_mask;
         v = expand2[GET_PLANE(data, 0)];
         v |= expand2[GET_PLANE(data, 2)] << 2;
@@ -144,7 +144,7 @@
     plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf];
     width >>= 3;
     for(x = 0; x < width; x++) {
-        data = vga_read_dword_le(vga, addr);
+        data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1));
         data &= plane_mask;
         v = expand2[GET_PLANE(data, 0)];
         v |= expand2[GET_PLANE(data, 2)] << 2;
@@ -177,7 +177,7 @@
     plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf];
     width >>= 3;
     for(x = 0; x < width; x++) {
-        data = vga_read_dword_le(vga, addr);
+        data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1));
         data &= plane_mask;
         v = expand4[GET_PLANE(data, 0)];
         v |= expand4[GET_PLANE(data, 1)] << 1;
@@ -209,7 +209,7 @@
     plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf];
     width >>= 3;
     for(x = 0; x < width; x++) {
-        data = vga_read_dword_le(vga, addr);
+        data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1));
         data &= plane_mask;
         v = expand4[GET_PLANE(data, 0)];
         v |= expand4[GET_PLANE(data, 1)] << 1;
@@ -242,6 +242,7 @@
     palette = vga->last_palette;
     width >>= 3;
     for(x = 0; x < width; x++) {
+        addr &= VGA_VRAM_SIZE - 1;
         PUT_PIXEL2(d, 0, palette[vga_read_byte(vga, addr + 0)]);
         PUT_PIXEL2(d, 1, palette[vga_read_byte(vga, addr + 1)]);
         PUT_PIXEL2(d, 2, palette[vga_read_byte(vga, addr + 2)]);