From 45c3770d595fb3b8c06a3ecb8ce7660ab8e2f18f Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Thu, 10 Feb 2022 11:56:44 -0700
Subject: [PATCH] Use VbeFarPtr to fix reading video modes

---
 src/os/bios/vbe.rs | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/os/bios/vbe.rs b/src/os/bios/vbe.rs
index 57e2805db8..78e0547128 100644
--- a/src/os/bios/vbe.rs
+++ b/src/os/bios/vbe.rs
@@ -5,19 +5,32 @@ use crate::os::OsVideoMode;
 
 use super::{ThunkData, VBE_CARD_INFO_ADDR, VBE_MODE_INFO_ADDR};
 
+#[derive(Clone, Copy, Debug)]
+#[repr(packed)]
+pub struct VbeFarPtr {
+    pub offset: u16,
+    pub segment: u16,
+}
+
+impl VbeFarPtr {
+    pub unsafe fn as_ptr<T>(&self) -> *const T {
+        (((self.segment as usize) << 4) + (self.offset as usize)) as *const T
+    }
+}
+
 #[derive(Clone, Copy, Debug)]
 #[repr(packed)]
 pub struct VbeCardInfo {
     pub signature: [u8; 4],
     pub version: u16,
-    pub oemstring: u32,
-    pub capabilities: u32,
-    pub videomodeptr: u32,
+    pub oemstring: VbeFarPtr,
+    pub capabilities: [u8; 4],
+    pub videomodeptr: VbeFarPtr,
     pub totalmemory: u16,
     pub oemsoftwarerev: u16,
-    pub oemvendornameptr: u32,
-    pub oemproductnameptr: u32,
-    pub oemproductrevptr: u32,
+    pub oemvendornameptr: VbeFarPtr,
+    pub oemproductnameptr: VbeFarPtr,
+    pub oemproductrevptr: VbeFarPtr,
     pub reserved: [u8; 222],
     pub oemdata: [u8; 256],
 }
@@ -74,7 +87,7 @@ impl VideoModeIter {
         unsafe { data.with(thunk10); }
         let mode_ptr = if data.eax == 0x004F {
             let card_info = unsafe { ptr::read(VBE_CARD_INFO_ADDR as *const VbeCardInfo) };
-            card_info.videomodeptr as *const u16
+            unsafe { card_info.videomodeptr.as_ptr::<u16>() }
         } else {
             error!("Failed to read VBE card info: 0x{:04X}", { data.eax });
             ptr::null()