From 2f514a5127feebcf4b827b30f830a4c1bd58ac01 Mon Sep 17 00:00:00 2001
From: Stanislav Motylkov <x86corez@gmail.com>
Date: Thu, 18 Jun 2026 00:55:27 +0300
Subject: [PATCH] [FREELDR] Workaround for BIOSes that report unusual geometry
 for CD-ROMs

This is needed for ISO filesystem driver to work correctly,
as it assumes 2048 bytes per sector for CD-ROM media.

Happens on 86Box with board `[i430FX] ASUS P/I-P55TP4XE`,
Bochs emulator with `01/17/97-i440FX-2A69HV3CC-00` BIOS,
and some other real machines.

CORE-20640
---
 boot/freeldr/freeldr/arch/i386/hwdisk.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/boot/freeldr/freeldr/arch/i386/hwdisk.c b/boot/freeldr/freeldr/arch/i386/hwdisk.c
index 316cca5bddf..2315c191a03 100644
--- a/boot/freeldr/freeldr/arch/i386/hwdisk.c
+++ b/boot/freeldr/freeldr/arch/i386/hwdisk.c
@@ -90,6 +90,7 @@ DiskOpen(CHAR* Path, OPENMODE OpenMode, ULONG* FileId)
     GEOMETRY Geometry;
     ULONGLONG SectorOffset;
     ULONGLONG SectorCount;
+    static BOOLEAN PrintForce = FALSE;
 
     if (DiskReadBufferSize == 0)
     {
@@ -141,6 +142,16 @@ DiskOpen(CHAR* Path, OPENMODE OpenMode, ULONG* FileId)
     if (!Context)
         return ENOMEM;
 
+    if (DriveType == CdromController && SectorSize != 2048)
+    {
+        /* Workaround for CORE-20640 */
+        if (!PrintForce)
+        {
+            ERR("BIOS reports BytesPerSector = %d for CD-ROM, forcing 2048\n", SectorSize);
+            PrintForce = TRUE;
+        }
+        SectorSize = 2048;
+    }
     Context->DriveNumber = DriveNumber;
     Context->IsFloppy = (DriveType == FloppyDiskPeripheral);
     Context->SectorSize = SectorSize;