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[FREELDR] Improve DiskGetExtendedDriveParameters()

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- Move BIOS-specific `EXTENDED_GEOMETRY` structure to pcdisk.c

- Zero out the transfer buffer for INT 13h, function 48h before
  invocation. This ensures that any random data is removed and
  that some broken BIOSes behave better.

- Use a more suitable type for the pointer to the transfer buffer,
  so that we can use more human-manageable member names in TRACEs
  instead of magic buffer offsets.
This commit is contained in:
Hermès Bélusca-Maïto
2025-09-28 19:30:27 +02:00
parent 1375320ac4
commit a0c427319f
2 changed files with 53 additions and 49 deletions
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86
boot/freeldr/freeldr/arch/i386/pc/pcdisk.c
View File

@@ -27,7 +27,7 @@ DBG_DEFAULT_CHANNEL(DISK);
/* Enable this line if you want to support multi-drive caching (increases FreeLdr size!) */
// #define CACHE_MULTI_DRIVES
#include <pshpack2.h>
#include <pshpack1.h>
typedef struct
{
@@ -74,6 +74,22 @@ typedef struct
UCHAR Reserved;
} I386_CDROM_SPEC_PACKET, *PI386_CDROM_SPEC_PACKET;
/*
* Extended disk geometry (Int13 / AH=48h)
* See also ntdddisk.h DISK_EX_INT13_INFO
*/
typedef struct _EXTENDED_GEOMETRY
{
USHORT Size;
USHORT Flags;
ULONG Cylinders;
ULONG Heads;
ULONG SectorsPerTrack;
ULONGLONG Sectors;
USHORT BytesPerSector;
ULONG PDPTE;
} EXTENDED_GEOMETRY, *PEXTENDED_GEOMETRY;
#include <poppack.h>
typedef struct _PC_DISK_DRIVE
@@ -295,21 +311,27 @@ DiskInt13ExtensionsSupported(IN UCHAR DriveNumber)
static BOOLEAN
DiskGetExtendedDriveParameters(
IN UCHAR DriveNumber,
IN PPC_DISK_DRIVE DiskDrive,
OUT PVOID Buffer,
IN USHORT BufferSize)
_In_ UCHAR DriveNumber,
_In_ PPC_DISK_DRIVE DiskDrive,
_Out_ PVOID Buffer,
_In_ USHORT BufferSize)
{
PEXTENDED_GEOMETRY Ptr = (PEXTENDED_GEOMETRY)BIOSCALLBUFFER;
REGS RegsIn, RegsOut;
PUSHORT Ptr = (PUSHORT)(BIOSCALLBUFFER);
TRACE("DiskGetExtendedDriveParameters(0x%x)\n", DriveNumber);
if (!DiskDrive->Int13ExtensionsSupported)
if (!DiskDrive->Int13ExtensionsSupported || (BufferSize < sizeof(*Ptr)))
return FALSE;
/* Initialize transfer buffer */
*Ptr = BufferSize;
/*
* Initialize the transfer buffer.
* NOTE: Zeroing out the buffer also helps avoiding the bug where Dell
* machines using PhoenixBIOS 4.0 Release 6.0 fail to correctly handle
* this function if Ptr->Flags is not 0 on entry.
*/
RtlZeroMemory(Ptr, sizeof(*Ptr)); // BufferSize;
Ptr->Size = BufferSize;
/*
* BIOS Int 13h, function 48h - Get drive parameters
@@ -325,7 +347,7 @@ DiskGetExtendedDriveParameters(
*/
RegsIn.b.ah = 0x48;
RegsIn.b.dl = DriveNumber;
RegsIn.x.ds = BIOSCALLBUFSEGMENT; // DS:SI -> result buffer
RegsIn.x.ds = BIOSCALLBUFSEGMENT;
RegsIn.w.si = BIOSCALLBUFOFFSET;
/* Get drive parameters */
@@ -336,22 +358,25 @@ DiskGetExtendedDriveParameters(
RtlCopyMemory(Buffer, Ptr, BufferSize);
#if DBG
TRACE("Size of buffer: 0x%x\n", Ptr[0]);
TRACE("Information flags: 0x%x\n", Ptr[1]);
TRACE("Number of physical cylinders on drive: %u\n", *(PULONG)&Ptr[2]);
TRACE("Number of physical heads on drive: %u\n", *(PULONG)&Ptr[4]);
TRACE("Number of physical sectors per track: %u\n", *(PULONG)&Ptr[6]);
TRACE("Total number of sectors on drive: %I64u\n", *(PULONGLONG)&Ptr[8]);
TRACE("Bytes per sector: %u\n", Ptr[12]);
if (Ptr[0] >= 0x1e)
TRACE("Size of buffer: 0x%x\n", Ptr->Size);
TRACE("Information flags: 0x%x\n", Ptr->Flags);
TRACE("Number of physical cylinders on drive: %u\n", Ptr->Cylinders);
TRACE("Number of physical heads on drive: %u\n", Ptr->Heads);
TRACE("Number of physical sectors per track: %u\n", Ptr->SectorsPerTrack);
TRACE("Total number of sectors on drive: %I64u\n", Ptr->Sectors);
TRACE("Bytes per sector: %u\n", Ptr->BytesPerSector);
if (Ptr->Size >= 0x1E)
{
// Ptr[13]: offset, Ptr[14]: segment
TRACE("EDD configuration parameters (DPTE): %x:%x\n", Ptr[14], Ptr[13]);
// LOWORD(Ptr->PDPTE): offset, HIWORD(Ptr->PDPTE): segment
USHORT Off = (USHORT)(Ptr->PDPTE & 0xFFFF); // ((PUSHORT)&Ptr->PDPTE)[0];
USHORT Seg = (USHORT)((Ptr->PDPTE >> 16) & 0xFFFF); // ((PUSHORT)&Ptr->PDPTE)[1];
TRACE("EDD configuration parameters (DPTE): %x:%x\n", Seg, Off);
/* The DPTE pointer is valid if it's != FFFF:FFFF (per the Enhanced Disk
* Drive Specification), but also, when it's != 0000:0000 (broken BIOSes) */
if (!(Ptr[13] == 0xFFFF && Ptr[14] == 0xFFFF) && !(Ptr[13] == 0 && Ptr[14] == 0))
if (Ptr->PDPTE != 0xFFFFFFFF && Ptr->PDPTE != 0)
{
PUCHAR SpecPtr = (PUCHAR)(ULONG_PTR)((Ptr[14] << 4) + Ptr[13]);
PUCHAR SpecPtr = (PUCHAR)(ULONG_PTR)((Seg << 4) + Off);
TRACE("SpecPtr: 0x%x\n", SpecPtr);
TRACE("Physical I/O port base address: 0x%x\n", *(PUSHORT)&SpecPtr[0]);
TRACE("Disk-drive control port address: 0x%x\n", *(PUSHORT)&SpecPtr[2]);
@@ -364,9 +389,9 @@ DiskGetExtendedDriveParameters(
TRACE("Drive options: 0x%x\n", *(PUSHORT)&SpecPtr[10]);
}
}
if (Ptr[0] >= 0x42)
if (Ptr->Size >= 0x42)
{
TRACE("Signature: 0x%x\n", Ptr[15]);
TRACE("Signature: 0x%x\n", ((PUSHORT)Ptr)[15]);
}
#endif // DBG
@@ -383,16 +408,11 @@ InitDriveGeometry(
ULONG Cylinders;
/* Get the extended geometry first */
DiskDrive->ExtGeometry.Size = sizeof(DiskDrive->ExtGeometry);
RtlZeroMemory(&DiskDrive->ExtGeometry, sizeof(DiskDrive->ExtGeometry));
Success = DiskGetExtendedDriveParameters(DriveNumber, DiskDrive,
&DiskDrive->ExtGeometry,
DiskDrive->ExtGeometry.Size);
if (!Success)
{
/* Failed, zero it out */
RtlZeroMemory(&DiskDrive->ExtGeometry, sizeof(DiskDrive->ExtGeometry));
}
else
sizeof(DiskDrive->ExtGeometry));
if (Success)
{
TRACE("DiskGetExtendedDriveParameters(0x%x) returned:\n"
"Cylinders : 0x%x\n"
@@ -575,9 +595,9 @@ PcDiskReadLogicalSectorsLBA(
IN ULONG SectorCount,
OUT PVOID Buffer)
{
PI386_DISK_ADDRESS_PACKET Packet = (PI386_DISK_ADDRESS_PACKET)BIOSCALLBUFFER;
REGS RegsIn, RegsOut;
ULONG RetryCount;
PI386_DISK_ADDRESS_PACKET Packet = (PI386_DISK_ADDRESS_PACKET)(BIOSCALLBUFFER);
/* Setup disk address packet */
RtlZeroMemory(Packet, sizeof(*Packet));

16
boot/freeldr/freeldr/include/disk.h
View File

@@ -33,22 +33,6 @@ typedef struct _GEOMETRY
#include <pshpack1.h>
/*
* Extended disk geometry (Int13 / AH=48h)
* See also ntdddisk.h DISK_EX_INT13_INFO
*/
typedef struct _EXTENDED_GEOMETRY
{
USHORT Size;
USHORT Flags;
ULONG Cylinders;
ULONG Heads;
ULONG SectorsPerTrack;
ULONGLONG Sectors;
USHORT BytesPerSector;
ULONG PDPTE;
} EXTENDED_GEOMETRY, *PEXTENDED_GEOMETRY;
/*
* Define the structure of a partition table entry
*/