[PATCH] Proof of concept interrupt wrapping

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

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Hello. We were discussing with Robert how to move BIOS interrupt
routines out of kernel. There are following possibilities:
1) Have a .lowmem section in every concerned module which will always be
placed in low memory. Currently in experimental.
Advantages:
  a) moving functions to modules is straightforward
  b) functions grow neither in size nor in complexity
Disadvantages:
  c) needs lowmem allocators in core
2) Make every function needing bios interrupts setup its own trampoline.
Due to complexity of trampolines it's not a real option
3) Have an universal routine grub_interrupt (int intno, struct
grub_cpu_interrupt_regs *regs) which will be used by C routine to do the
interrupt calls. This would move the complexity from asm to C.
Advantages:
a) simplicity in core
b) complexity moved to a more readable language
c)  we can also rename grub_interrupt to grub_interrupt_real and make
grub_interrupt dprintf registers before and after the call. This would
make debugging BIOS quirks easier.
Disadvantages:
a) Moving functions needs effort
b) C functions are probably bigger but it may be offset by possibility
of inlining functions
c) repeadetly changing from/to real mode is an overhead when executing
multiple interrupts in series. Fortunately this condition is rare in our
codebase and is only on non performance-critical parts like halting.
d) Some functions aren't covered by this. At least grub_pxe_call is in
this case. But we can use method 2 for them

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko


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=== modified file 'conf/i386-pc.rmk'
--- conf/i386-pc.rmk	2009-12-25 22:06:52 +0000
+++ conf/i386-pc.rmk	2009-12-31 12:07:51 +0000
@@ -64,7 +64,7 @@
 	partition.h msdos_partition.h reader.h symbol.h term.h time.h types.h \
 	machine/biosdisk.h machine/boot.h machine/console.h machine/init.h \
 	machine/memory.h machine/loader.h machine/vga.h machine/vbe.h \
-	machine/kernel.h machine/pxe.h i386/pit.h list.h handler.h command.h i18n.h
+	machine/kernel.h machine/pxe.h i386/pit.h list.h handler.h command.h i18n.h machine/int.h
 kernel_img_CFLAGS = $(COMMON_CFLAGS)  $(TARGET_IMG_CFLAGS)
 kernel_img_ASFLAGS = $(COMMON_ASFLAGS)
 kernel_img_LDFLAGS = $(COMMON_LDFLAGS) $(TARGET_IMG_LDFLAGS)$(GRUB_KERNEL_MACHINE_LINK_ADDR) $(COMMON_CFLAGS)

=== modified file 'disk/i386/pc/biosdisk.c'
--- disk/i386/pc/biosdisk.c	2009-12-10 18:15:20 +0000
+++ disk/i386/pc/biosdisk.c	2009-12-31 12:07:51 +0000
@@ -19,6 +19,7 @@
 #include <grub/machine/biosdisk.h>
 #include <grub/machine/memory.h>
 #include <grub/machine/kernel.h>
+#include <grub/machine/int.h>
 #include <grub/disk.h>
 #include <grub/dl.h>
 #include <grub/mm.h>
@@ -28,6 +29,59 @@
 #include <grub/term.h>
 
 static int cd_drive = 0;
+static int grub_biosdisk_rw_int13_extensions (int ah, int drive, void *dap);
+
+static int grub_biosdisk_get_num_floppies (void)
+{
+  struct grub_cpu_int_registers regs;
+  int drive;
+
+  /* reset the disk system first */
+  regs.ax = 0;
+  regs.dx = 0;
+  regs.flags = GRUB_CPU_INT_FLAGS_DEFAULT;
+
+  grub_cpu_interrupt (0x13, &regs);
+
+  for (drive = 0; drive < 2; drive++)
+    {
+      regs.flags = GRUB_CPU_INT_FLAGS_DEFAULT | GRUB_CPU_INT_FLAGS_CARRY;
+      regs.dx = drive;
+
+      /* call GET DISK TYPE */
+      regs.ax = 0x1500;
+      grub_cpu_interrupt (0x13, &regs);
+      if (regs.flags & GRUB_CPU_INT_FLAGS_CARRY)
+	break;
+
+      /* check if this drive exists */
+      if (!(regs.ax & 0x300))
+	break;
+    }
+
+  return drive;
+}
+
+/*
+ *   Call IBM/MS INT13 Extensions (int 13 %ah=AH) for DRIVE. DAP
+ *   is passed for disk address packet. If an error occurs, return
+ *   non-zero, otherwise zero.
+ */
+
+static int 
+grub_biosdisk_rw_int13_extensions (int ah, int drive, void *dap)
+{
+  struct grub_cpu_int_registers regs;
+  regs.ax = ah << 8;
+  /* compute the address of disk_address_packet */
+  regs.ds = (((grub_addr_t) dap) & 0xffff0000) >> 4;
+  regs.si = (((grub_addr_t) dap) & 0xffff);
+  regs.dx = drive;
+  regs.flags = GRUB_CPU_INT_FLAGS_DEFAULT;
+
+  grub_cpu_interrupt (0x13, &regs);
+  return regs.ax >> 8;
+}
 
 static int
 grub_biosdisk_get_drive (const char *name)

=== modified file 'include/grub/i386/pc/biosdisk.h'
--- include/grub/i386/pc/biosdisk.h	2009-06-10 21:04:23 +0000
+++ include/grub/i386/pc/biosdisk.h	2009-12-31 12:07:51 +0000
@@ -106,7 +106,6 @@
   grub_uint64_t block;
 } __attribute__ ((packed));
 
-int EXPORT_FUNC(grub_biosdisk_rw_int13_extensions) (int ah, int drive, void *dap);
 int EXPORT_FUNC(grub_biosdisk_rw_standard) (int ah, int drive, int coff, int hoff,
 			       int soff, int nsec, int segment);
 int EXPORT_FUNC(grub_biosdisk_check_int13_extensions) (int drive);
@@ -118,7 +117,6 @@
 					 unsigned long *cylinders,
 					 unsigned long *heads,
 					 unsigned long *sectors);
-int EXPORT_FUNC(grub_biosdisk_get_num_floppies) (void);
 
 void grub_biosdisk_init (void);
 void grub_biosdisk_fini (void);

=== added file 'include/grub/i386/pc/int.h'
--- include/grub/i386/pc/int.h	1970-01-01 00:00:00 +0000
+++ include/grub/i386/pc/int.h	2009-12-31 12:07:51 +0000
@@ -0,0 +1,50 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 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/>.
+ */
+
+#ifndef GRUB_INTERRUPT_MACHINE_HEADER
+#define GRUB_INTERRUPT_MACHINE_HEADER	1
+
+#include <grub/symbol.h>
+
+struct grub_cpu_int_registers
+{
+  grub_uint16_t bx;
+  grub_uint16_t es;
+  grub_uint16_t cx;
+  grub_uint16_t ax;
+  grub_uint16_t dx;
+  grub_uint16_t ds;
+  grub_uint16_t di;
+  grub_uint16_t flags;
+  grub_uint16_t si;
+};
+
+#define  GRUB_CPU_INT_FLAGS_CARRY     0x1
+#define  GRUB_CPU_INT_FLAGS_PARITY    0x4
+#define  GRUB_CPU_INT_FLAGS_ADJUST    0x10
+#define  GRUB_CPU_INT_FLAGS_ZERO      0x40
+#define  GRUB_CPU_INT_FLAGS_SIGN      0x80
+#define  GRUB_CPU_INT_FLAGS_TRAP      0x100
+#define  GRUB_CPU_INT_FLAGS_INTERRUPT 0x200
+#define  GRUB_CPU_INT_FLAGS_DIRECTION 0x400
+#define  GRUB_CPU_INT_FLAGS_OVERFLOW  0x800
+#define  GRUB_CPU_INT_FLAGS_DEFAULT   GRUB_CPU_INT_FLAGS_INTERRUPT
+
+void EXPORT_FUNC (grub_cpu_interrupt) (grub_uint8_t intno, struct grub_cpu_int_registers *regs);
+
+#endif

=== modified file 'kern/i386/pc/startup.S'
--- kern/i386/pc/startup.S	2009-12-25 22:01:32 +0000
+++ kern/i386/pc/startup.S	2009-12-31 12:07:51 +0000
@@ -567,44 +567,6 @@
 #include "../loader.S"
 
 /*
- *   int grub_biosdisk_rw_int13_extensions (int ah, int drive, void *dap)
- *
- *   Call IBM/MS INT13 Extensions (int 13 %ah=AH) for DRIVE. DAP
- *   is passed for disk address packet. If an error occurs, return
- *   non-zero, otherwise zero.
- */
-
-FUNCTION(grub_biosdisk_rw_int13_extensions)
-	pushl	%ebp
-	pushl	%esi
-
-	/* compute the address of disk_address_packet */
-	movw	%cx, %si
-	xorw	%cx, %cx
-	shrl	$4, %ecx	/* save the segment to cx */
-
-	/* ah */
-	movb	%al, %dh
-	/* enter real mode */
-	call	prot_to_real
-
-	.code16
-	movb	%dh, %ah
-	movw	%cx, %ds
-	int	$0x13		/* do the operation */
-	movb	%ah, %dl	/* save return value */
-	/* back to protected mode */
-	DATA32	call	real_to_prot
-	.code32
-
-	movb	%dl, %al	/* return value in %eax */
-
-	popl	%esi
-	popl	%ebp
-
-	ret
-
-/*
  *   int grub_biosdisk_rw_standard (int ah, int drive, int coff, int hoff,
  *                                  int soff, int nsec, int segment)
  *
@@ -862,43 +824,6 @@
 
 
 /*
- * int grub_biosdisk_get_num_floppies (void)
- */
-FUNCTION(grub_biosdisk_get_num_floppies)
-	pushl	%ebp
-
-	xorl	%edx, %edx
-	call	prot_to_real
-
-	.code16
-	/* reset the disk system first */
-	int	$0x13
-1:
-	stc
-
-	/* call GET DISK TYPE */
-	movb	$0x15, %ah
-	int	$0x13
-
-	jc	2f
-
-	/* check if this drive exists */
-	testb	$0x3, %ah
-	jz	2f
-
-	incb	%dl
-	cmpb	$2, %dl
-	jne	1b
-2:
-	DATA32	call	real_to_prot
-	.code32
-
-	movl	%edx, %eax
-	popl	%ebp
-	ret
-
-
-/*
  *
  * grub_get_memsize(i) :  return the memory size in KB. i == 0 for conventional
  *		memory, i == 1 for extended memory
@@ -2142,3 +2067,74 @@
 	popl	%esi
 	popl	%ebp
 	ret
+
+FUNCTION(grub_cpu_interrupt)
+	pushl    %ebp
+	pushl    %esi
+	pushl    %edi
+	pushl    %ebx
+	pushl    %edx
+	movb     %al, intno
+	movl     %edx, %esi
+
+	movl     0(%esi), %ebx
+	movl	 4(%esi), %ecx
+	movl     8(%esi), %edx
+	movl     12(%esi), %edi
+	movw     16(%esi), %si
+
+	call    prot_to_real
+	.code16
+	movl    %edi, %eax
+	shrl    $16, %eax
+	push    %ax
+
+	movl    %ebx, %eax
+	shrl    $16, %eax
+	movw    %ax, %es
+	
+	movl    %edx, %eax
+	shrl    $16, %eax
+	movw    %ax, %ds
+
+	movl    %ecx, %eax
+	shrl    $16, %eax
+
+	popf
+	.byte   0xcd
+intno:	
+	.byte   0
+
+	pushf
+	andl    $0xffff, %ebx
+	andl    $0xffff, %ecx
+	andl    $0xffff, %edx
+	andl    $0xffff, %edi
+
+	shll    $16, %eax
+	orl     %eax, %ecx
+
+	movw    %ds, %ax
+	shll    $16, %eax
+	orl     %eax, %edx
+
+	pop     %ax
+	shll    $16, %eax
+	orl     %eax, %edi
+
+	DATA32  call	real_to_prot
+	.code32
+	pushl    %esi
+	movl     4(%esp), %esi
+	movl     %ebx, 0(%esi)
+	movl     %ecx, 4(%esi)
+	movl     %edx, 8(%esi)
+	movl     %edi, 12(%esi)
+	popl     %eax
+	movw     %ax, 16(%esi)
+	popl     %eax
+	popl	 %ebx
+	popl	 %edi
+	popl	 %esi
+	popl     %ebp
+	ret


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