automake commit without merge history

grub-core/commands/i386/pc/drivemap_int13h.S

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+/* drivemap_int13h.S - interrupt handler for the BIOS drive remapper */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2008, 2009  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/symbol.h>
+
+#define INT13H_OFFSET(x) ((x) - LOCAL (base))
+
+.code16
+
+/* Copy starts here.  When deployed, this code must be segment-aligned.  */
+
+/* The replacement int13 handler.   Preserve all registers.  */
+FUNCTION(grub_drivemap_handler)
+LOCAL (base):
+	/* Save %dx for future restore. */
+	push	%dx
+	/* Push flags. Used to simulate interrupt with original flags. */
+	pushf
+
+	/* Map the drive number (always in DL).  */
+	push	%ax
+	push	%bx
+	movw	$INT13H_OFFSET(LOCAL (mapstart)), %bx
+
+more_remaining:
+	movw	%cs:(%bx), %ax
+	cmpb	%ah, %al
+	jz	not_found /* DRV=DST => map end - drive not remapped, keep DL.  */
+	inc	%bx
+	inc	%bx
+	cmpb	%dl, %al
+	jnz	more_remaining /* Not found, but more remaining, loop.  */
+	movb	%ah, %dl /* Found - drive remapped, modify DL.  */
+
+not_found:
+	pop	%bx
+	pop	%ax
+
+	/* If the call isn't ah=0x8 or ah=0x15 we must restore %dx.  */
+	cmpb	$0x8, %ah
+	jz	norestore
+	cmpb	$0x15, %ah
+	jz	norestore
+
+	/* Restore flags.  */
+	popf
+	pushf
+
+	lcall *%cs:INT13H_OFFSET (LOCAL (oldhandler))
+
+	push	%bp
+	mov	%sp, %bp
+
+tail:
+	/* Save new flags below %esp so the caller will recieve new flags.  */
+	pushf
+	pop	%dx
+	mov	%dx, 8(%bp)
+
+	pop	%bp
+
+	/* Restore %dx.  */
+	pop	%dx
+	iret
+
+norestore:
+
+	/* Restore flags.  */
+	popf
+	pushf
+
+	lcall *%cs:INT13H_OFFSET (LOCAL (oldhandler))
+
+	push	%bp
+	mov	%sp, %bp
+
+	/* Save %dx. So it won't be restored to original value.  */
+	mov	%dx, 2(%bp)
+
+	jmp tail
+
+/* Far pointer to the old handler.  Stored as a CS:IP in the style of real-mode
+   IVT entries (thus PI:SC in mem).  */
+VARIABLE(grub_drivemap_oldhandler)
+LOCAL (oldhandler):
+	.word 0x0, 0x0
+
+/* This label MUST be at the end of the copied block, since the installer code
+   reserves additional space for mappings at runtime and copies them over it.  */
+	.align 2
+	
+VARIABLE(grub_drivemap_mapstart)
+LOCAL (mapstart):
+	.byte 0