[FREELDR] linuxboot: It doesn't need the BIOS boot drive number and partition.

Also document a little bit the RootDevice field in the boot sector;
add SAL2 annotations.

boot/freeldr/freeldr/arch/amd64/linux.S

@@ -23,8 +23,6 @@
 
 EXTERN DiskStopFloppyMotor:PROC
 EXTERN Relocator16Boot:PROC
-EXTERN FrldrBootDrive:BYTE
-EXTERN FrldrBootPartition:DWORD
 
 .code64
 
@@ -32,12 +30,11 @@ Regs:
     .space REGS_SIZE
 
 /*
- * VOID __cdecl BootLinuxKernel(
+ * VOID __cdecl
- *     IN ULONG KernelSize<ecx>,
+ * BootLinuxKernel(
- *     IN PVOID KernelCurrentLoadAddress<rdx>,
+ *     _In_ ULONG KernelSize<ecx>,
- *     IN PVOID KernelTargetLoadAddress<r8>,
+ *     _In_ PVOID KernelCurrentLoadAddress<rdx>,
- *     IN UCHAR DriveNumber<r9b>,
+ *     _In_ PVOID KernelTargetLoadAddress<r8>);
- *     IN ULONG PartitionNumber<rsp+40>);
  */
 PUBLIC BootLinuxKernel
 BootLinuxKernel:
@@ -47,7 +44,6 @@ BootLinuxKernel:
     mov dword ptr [r11 +  8], ecx
     mov qword ptr [r11 + 16], rdx
     mov qword ptr [r11 + 24], r8
-    mov  byte ptr [r11 + 32], r9b
 
     /* Save non-volatile registers */
     push rsi
@@ -67,25 +63,6 @@ BootLinuxKernel:
     mov word ptr [Regs + REGS_FS], ax
     mov word ptr [Regs + REGS_GS], ax
 
-    /* Set the boot drive */
-    xor edx, edx
-    mov dl, byte ptr [r11 + 32]
-    test dl, dl
-    jnz set_part
-    mov dl, byte ptr /*ds:*/[FrldrBootDrive]
-
-    /* Set the boot partition */
-set_part:
-    mov eax, dword ptr [r11 + 40]
-    test eax, eax
-    jnz continue
-    mov eax, dword ptr /*ds:*/[FrldrBootPartition]
-continue:
-    /* Store the 1-byte truncated partition number in DH */
-    mov dh, al
-
-    mov dword ptr [Regs + REGS_EDX], edx
-
     /*
      * Relocate the kernel image to its final destination (can be as low as 0x10000).
      * The reason we can overwrite low memory is because this code executes

boot/freeldr/freeldr/arch/i386/linux.S

@@ -23,8 +23,6 @@
 
 EXTERN _DiskStopFloppyMotor:PROC
 EXTERN _Relocator16Boot:PROC
-EXTERN _FrldrBootDrive:BYTE
-EXTERN _FrldrBootPartition:DWORD
 
 .code32
 
@@ -32,12 +30,11 @@ Regs:
     .space REGS_SIZE
 
 /*
- * VOID __cdecl BootLinuxKernel(
+ * VOID __cdecl
- *     IN ULONG KernelSize,
+ * BootLinuxKernel(
- *     IN PVOID KernelCurrentLoadAddress,
+ *     _In_ ULONG KernelSize,
- *     IN PVOID KernelTargetLoadAddress,
+ *     _In_ PVOID KernelCurrentLoadAddress,
- *     IN UCHAR DriveNumber,
+ *     _In_ PVOID KernelTargetLoadAddress);
- *     IN ULONG PartitionNumber);
  */
 PUBLIC _BootLinuxKernel
 _BootLinuxKernel:
@@ -52,25 +49,6 @@ _BootLinuxKernel:
     mov word ptr [Regs + REGS_FS], ax
     mov word ptr [Regs + REGS_GS], ax
 
-    /* Set the boot drive */
-    xor edx, edx
-    mov dl, byte ptr [esp + 16]
-    test dl, dl
-    jnz set_part
-    mov dl, byte ptr ds:[_FrldrBootDrive]
-
-    /* Set the boot partition */
-set_part:
-    mov eax, dword ptr [esp + 20]
-    test eax, eax
-    jnz continue
-    mov eax, dword ptr ds:[_FrldrBootPartition]
-continue:
-    /* Store the 1-byte truncated partition number in DH */
-    mov dh, al
-
-    mov dword ptr [Regs + REGS_EDX], edx
-
     /*
      * Relocate the kernel image to its final destination (can be as low as 0x10000).
      * The reason we can overwrite low memory is because this code executes

boot/freeldr/freeldr/include/linux.h

@@ -129,18 +129,17 @@ typedef struct
 #include <poppack.h>
 
 // Implemented in linux.S
-VOID __cdecl BootLinuxKernel(
+VOID __cdecl
-    IN ULONG KernelSize,
+BootLinuxKernel(
-    IN PVOID KernelCurrentLoadAddress,
+    _In_ ULONG KernelSize,
-    IN PVOID KernelTargetLoadAddress,
+    _In_ PVOID KernelCurrentLoadAddress,
-    IN UCHAR DriveNumber,
+    _In_ PVOID KernelTargetLoadAddress);
-    IN ULONG PartitionNumber);
 
 ARC_STATUS
 LoadAndBootLinux(
-    IN ULONG Argc,
+    _In_ ULONG Argc,
-    IN PCHAR Argv[],
+    _In_ PCHAR Argv[],
-    IN PCHAR Envp[]);
+    _In_ PCHAR Envp[]);
 
 #endif /* _M_IX86 || _M_AMD64 */
 

boot/freeldr/freeldr/linuxboot.c

@@ -20,6 +20,7 @@
 /*
  * The x86 Linux Boot Protocol is explained at:
  * https://www.kernel.org/doc/Documentation/x86/boot.txt
+ * https://www.linux.it/~rubini/docs/boot/boot.html
  */
 
 #if defined(_M_IX86) || defined(_M_AMD64)
@@ -84,21 +85,29 @@ RemoveQuotes(
 
 ARC_STATUS
 LoadAndBootLinux(
-    IN ULONG Argc,
+    _In_ ULONG Argc,
-    IN PCHAR Argv[],
+    _In_ PCHAR Argv[],
-    IN PCHAR Envp[])
+    _In_ PCHAR Envp[])
 {
     ARC_STATUS Status;
     PCSTR Description;
     PCSTR ArgValue;
     PCSTR BootPath;
-    UCHAR DriveNumber = 0;
-    ULONG PartitionNumber = 0;
     ULONG LinuxKernel = 0;
     ULONG LinuxInitrdFile = 0;
     FILEINFORMATION FileInfo;
     CHAR ArcPath[MAX_PATH];
 
+#if DBG
+    /* Ensure the boot type is the one expected */
+    ArgValue = GetArgumentValue(Argc, Argv, "BootType");
+    if (!ArgValue || !*ArgValue || _stricmp(ArgValue, "Linux") != 0)
+    {
+        ERR("Unexpected boot type '%s', aborting\n", ArgValue ? ArgValue : "n/a");
+        return EINVAL;
+    }
+#endif
+
     Description = GetArgumentValue(Argc, Argv, "LoadIdentifier");
     if (Description && *Description)
         RtlStringCbPrintfA(LinuxBootDescription, sizeof(LinuxBootDescription), "Loading %s...", Description);
@@ -125,10 +134,10 @@ LoadAndBootLinux(
         ArgValue = GetArgumentValue(Argc, Argv, "BootDrive");
         if (ArgValue && *ArgValue)
         {
-            DriveNumber = DriveMapGetBiosDriveNumber(ArgValue);
+            UCHAR DriveNumber = DriveMapGetBiosDriveNumber(ArgValue);
 
             /* Retrieve the boot partition (not optional and cannot be zero) */
-            PartitionNumber = 0;
+            ULONG PartitionNumber = 0;
             ArgValue = GetArgumentValue(Argc, Argv, "BootPartition");
             if (ArgValue && *ArgValue)
                 PartitionNumber = atoi(ArgValue);
@@ -152,17 +161,6 @@ LoadAndBootLinux(
         }
     }
 
-    /* If we haven't retrieved the BIOS drive and partition numbers above, do it now */
-    if (PartitionNumber == 0)
-    {
-        /* Retrieve the BIOS drive and partition numbers */
-        if (!DissectArcPath(BootPath, NULL, &DriveNumber, &PartitionNumber))
-        {
-            /* This is not a fatal failure, but just an inconvenience: display a message */
-            TRACE("DissectArcPath(%s) failed to retrieve BIOS drive and partition numbers.\n", BootPath);
-        }
-    }
-
     /* Get the kernel name */
     LinuxKernelName = GetArgumentValue(Argc, Argv, "Kernel");
     if (!LinuxKernelName || !*LinuxKernelName)
@@ -240,9 +238,22 @@ LoadAndBootLinux(
             goto LinuxBootFailed;
     }
 
-    // If the default root device is set to FLOPPY (0000h), change to /dev/fd0 (0200h)
+    /*
-    if (LinuxBootSector->RootDevice == 0x0000)
+     * If the default root device is set to FLOPPY (0000h), change to /dev/fd0 (0200h).
-        LinuxBootSector->RootDevice = 0x0200;
+     * For a list of majors, see
+     * https://github.com/torvalds/linux/blob/master/include/uapi/linux/major.h
+     * For some examples of (decoded) root devices values, see
+     * https://github.com/torvalds/linux/blob/cc89c63e2/include/linux/root_dev.h
+     *
+     * NOTE: The RootDevice field is deprecated since commits
+     * https://github.com/torvalds/linux/commit/079f85e62
+     * https://github.com/torvalds/linux/commit/7448e8e5d
+     */
+#define NODEV           0
+#define FLOPPY_MAJOR    2
+#define makedev(maj, min)   (((maj) << 8) | (min))
+    if (LinuxBootSector->RootDevice == NODEV)
+        LinuxBootSector->RootDevice = makedev(FLOPPY_MAJOR, 0);
 
     if (LinuxSetupSector->Version >= 0x0202)
     {
@@ -271,8 +282,7 @@ LoadAndBootLinux(
     BootLinuxKernel(LinuxKernelSize, LinuxKernelLoadAddress,
                     (LinuxSetupSector->LoadFlags & LINUX_FLAG_LOAD_HIGH)
                         ? (PVOID)LINUX_KERNEL_LOAD_ADDRESS /* == 0x100000 */
-                        : (PVOID)0x10000,
+                        : (PVOID)0x10000);
-                    DriveNumber, PartitionNumber);
     /* Must not return! */
     return ESUCCESS;