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Re: [PATCH] Kernel support for VESA Bios Extension


From: Vesa Jääskeläinen
Subject: Re: [PATCH] Kernel support for VESA Bios Extension
Date: Thu, 14 Jul 2005 23:36:53 +0300
User-agent: Mozilla Thunderbird (Windows/20050412)

Marco Gerards wrote:

I would like to hear comments about the patch. I tried to implement
most commonly needed functions, so you can't do everything with
this. As I didn't need to use every function in my frame buffer
console test, some things might not work. But I tried to make my best
to proof read every function.

Can you please make sure you are using the GCS for coding style?
Please have a look at the other sourcecode and the GCS (GNU Coding
Standards) first:

http://www.gnu.org/prep/standards/

It is important for us to have a single and consistent coding style.
If you have questions about either GRUB or the coding style you are of
course free to ask.

Perhaps this is a bit closer to requirement?

If there still are issues on formatting could you specify what issues you are thinking on.

Thanks,
Vesa Jääskeläinen
diff -ruN grub2/ChangeLog grub2.vbe/ChangeLog
--- grub2/ChangeLog     2005-07-13 01:36:43.000000000 +0300
+++ grub2.vbe/ChangeLog 2005-07-16 15:07:01.132381816 +0300
@@ -1,3 +1,21 @@
+2005-07-14  Vesa Jaaskelainen  <address@hidden>
+
+       * conf/i386-pc.rmk (kernel_img_HEADERS): Added machine/vbe.h.
+       * kern/i386/pc/startup.S: Updated Global Descriptor table's
+       descriptions.
+       (grub_vbe_get_controller_info): New function.
+       (grub_vbe_get_mode_info): Likewise.
+       (grub_vbe_set_mode): Likewise.
+       (grub_vbe_get_mode): Likewise.
+       (grub_vbe_set_memory_window): Likewise.
+       (grub_vbe_get_memory_window): Likewise.
+       (grub_vbe_set_scanline_length): Likewise.
+       (grub_vbe_get_scanline_length): Likewise.
+       (grub_vbe_set_display_start): Likewise.
+       (grub_vbe_get_display_start): Likewise.
+       (grub_vbe_set_palette_data): Likewise.
+       * include/grub/i386/pc/vbe.h: New file.
+
 2005-07-12  Hollis Blanchard  <address@hidden>
 
        * disk/powerpc/ieee1275/ofdisk.c (grub_ofdisk_open): dprintf the
diff -ruN grub2/conf/i386-pc.rmk grub2.vbe/conf/i386-pc.rmk
--- grub2/conf/i386-pc.rmk      2005-07-10 10:57:49.000000000 +0300
+++ grub2.vbe/conf/i386-pc.rmk  2005-07-15 18:10:05.000000000 +0300
@@ -33,7 +33,8 @@
        file.h fs.h kernel.h loader.h misc.h mm.h net.h rescue.h symbol.h \
        term.h types.h machine/biosdisk.h machine/boot.h \
        machine/console.h machine/init.h machine/memory.h \
-       machine/loader.h partition.h pc_partition.h machine/time.h machine/vga.h
+       machine/loader.h partition.h pc_partition.h machine/time.h 
machine/vga.h \
+       machine/vbe.h
 kernel_img_CFLAGS = $(COMMON_CFLAGS)
 kernel_img_ASFLAGS = $(COMMON_ASFLAGS)
 kernel_img_LDFLAGS = -nostdlib -Wl,-N,-Ttext,8200
diff -ruN grub2/include/grub/i386/pc/vbe.h grub2.vbe/include/grub/i386/pc/vbe.h
--- grub2/include/grub/i386/pc/vbe.h    1970-01-01 02:00:00.000000000 +0200
+++ grub2.vbe/include/grub/i386/pc/vbe.h        2005-07-16 17:21:40.815083344 
+0300
@@ -0,0 +1,180 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2005  Free Software Foundation, Inc.
+ *
+ *  This program 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 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 this program; if not, write to the Free Software
+ *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef GRUB_VBE_MACHINE_HEADER
+#define GRUB_VBE_MACHINE_HEADER        1
+
+#include <grub/symbol.h>
+#include <grub/types.h>
+
+/*
+ * Note:
+ *
+ * Please refer to VESA BIOS Extension 3.0 Specification for more descriptive
+ * meanings of following structures and how they should be used.
+ *
+ * I have tried to maintain field name comatibility against specification while
+ * following naming convetions used in GRUB.
+ */
+
+typedef grub_uint32_t  grub_vbe_farptr_t;
+typedef grub_uint32_t  grub_vbe_physptr_t;
+typedef grub_uint32_t  grub_vbe_status_t;
+
+struct grub_vbe_info_block
+{
+  grub_uint8_t signature[4];
+  grub_uint16_t version;
+
+  grub_vbe_farptr_t oem_string_ptr;
+  grub_uint32_t capabilities;
+  grub_vbe_farptr_t video_mode_ptr;
+  grub_uint16_t total_memory;
+
+  grub_uint16_t oem_software_rev;
+  grub_vbe_farptr_t oem_vendor_name_ptr;
+  grub_vbe_farptr_t oem_product_name_ptr;
+  grub_vbe_farptr_t oem_product_rev_ptr;
+
+  grub_uint8_t reserved[222];
+
+  grub_uint8_t oem_data[256];
+} __attribute__ ((packed));
+
+struct grub_vbe_mode_info_block
+{
+  /* Mandory information for all VBE revisions */
+  grub_uint16_t mode_attributes;
+  grub_uint8_t win_a_attributes;
+  grub_uint8_t win_b_attributes;
+  grub_uint16_t win_granularity;
+  grub_uint16_t win_size;
+  grub_uint16_t win_a_segment;
+  grub_uint16_t win_b_segment;
+  grub_vbe_farptr_t win_func_ptr;
+  grub_uint16_t bytes_per_scan_line;
+
+  /* Mandory information for VBE 1.2 and above */
+  grub_uint16_t x_resolution;
+  grub_uint16_t y_resolution;
+  grub_uint8_t x_char_size;
+  grub_uint8_t y_char_size;
+  grub_uint8_t number_of_planes;
+  grub_uint8_t bits_per_pixel;
+  grub_uint8_t number_of_banks;
+  grub_uint8_t memory_model;
+  grub_uint8_t bank_size;
+  grub_uint8_t number_of_image_pages;
+  grub_uint8_t reserved;
+
+  /* Direct Color fields (required for direct/6 and YUV/7 memory models) */
+  grub_uint8_t red_mask_size;
+  grub_uint8_t red_field_position;
+  grub_uint8_t green_mask_size;
+  grub_uint8_t green_field_position;
+  grub_uint8_t blue_mask_size;
+  grub_uint8_t blue_field_position;
+  grub_uint8_t rsvd_mask_size;
+  grub_uint8_t rsvd_field_position;
+  grub_uint8_t direct_color_mode_info;
+
+  /* Mandory information for VBE 2.0 and above */
+  grub_vbe_physptr_t phys_base_addr;
+  grub_uint32_t reserved2;
+  grub_uint16_t reserved3;
+
+  /* Mandory information for VBE 3.0 and above */
+  grub_uint16_t lin_bytes_per_scan_line;
+  grub_uint8_t bnk_number_of_image_pages;
+  grub_uint8_t lin_number_of_image_pages;
+  grub_uint8_t lin_red_mask_size;
+  grub_uint8_t lin_red_field_position;
+  grub_uint8_t lin_green_mask_size;
+  grub_uint8_t lin_green_field_position;
+  grub_uint8_t lin_blue_mask_size;
+  grub_uint8_t lin_blue_field_position;
+  grub_uint8_t lin_rsvd_mask_size;
+  grub_uint8_t lin_rsvd_field_position;
+  grub_uint32_t max_pixel_clock;
+
+  /*
+   * Reserved field to make structure to be 256 bytes long, VESA BIOS 
+   * Extension 3.0 Specification says to reserve 189 bytes here but 
+   * that doesn't make structure to be 256 bytes. So additional one is 
+   * added here.
+   */
+  grub_uint8_t reserved4[189+1];
+} __attribute__ ((packed));
+
+struct grub_vbe_crtc_info_block
+{
+  grub_uint16_t horizontal_total;
+  grub_uint16_t horizontal_sync_start;
+  grub_uint16_t horizontal_sync_end;
+  grub_uint16_t vertical_total;
+  grub_uint16_t vertical_sync_start;
+  grub_uint16_t vertical_sync_end;
+  grub_uint8_t flags;
+  grub_uint32_t pixel_clock;
+  grub_uint16_t refresh_rate;
+  grub_uint8_t reserved[40];
+} __attribute__ ((packed));
+
+struct grub_vbe_palette_data
+{
+  grub_uint8_t blue;
+  grub_uint8_t green;
+  grub_uint8_t red;
+  grub_uint8_t aligment;
+} __attribute__ ((packed));
+
+/* Call VESA BIOS 0x4f00 to get VBE Controller Information, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_controller_info) (struct 
grub_vbe_info_block *controller_info);
+
+/* Call VESA BIOS 0x4f01 to get VBE Mode Information, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_mode_info) (grub_uint32_t mode, 
struct grub_vbe_mode_info_block *mode_info);
+
+/* Call VESA BIOS 0x4f02 to set video mode, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_set_mode) (grub_uint32_t mode, struct 
grub_vbe_crtc_info_block *crtc_info);
+
+/* Call VESA BIOS 0x4f03 to return current VBE Mode, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_mode) (grub_uint32_t *mode);
+
+/* Call VESA BIOS 0x4f05 to set memory window, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_set_memory_window) (grub_uint32_t 
window, grub_uint32_t position);
+
+/* Call VESA BIOS 0x4f05 to return memory window, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_memory_window) (grub_uint32_t 
window, grub_uint32_t *position);
+
+/* Call VESA BIOS 0x4f06 to set scanline length (in bytes), return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_set_scanline_length) (grub_uint32_t 
length);
+
+/* Call VESA BIOS 0x4f06 to return scanline length (in bytes), return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_scanline_length) (grub_uint32_t 
*length);
+
+/* Call VESA BIOS 0x4f07 to set display start, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_set_display_start) (grub_uint32_t x, 
grub_uint32_t y);
+
+/* Call VESA BIOS 0x4f07 to get display start, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_get_display_start) (grub_uint32_t *x, 
grub_uint32_t *y);
+
+/* Call VESA BIOS 0x4f09 to set palette data, return status */
+grub_vbe_status_t EXPORT_FUNC(grub_vbe_set_palette_data) (grub_uint32_t 
color_count, grub_uint32_t start_index, struct grub_vbe_palette_data 
*palette_data);
+
+#endif /* ! GRUB_VBE_MACHINE_HEADER */
diff -ruN grub2/kern/i386/pc/startup.S grub2.vbe/kern/i386/pc/startup.S
--- grub2/kern/i386/pc/startup.S        2004-04-04 16:46:02.000000000 +0300
+++ grub2.vbe/kern/i386/pc/startup.S    2005-07-16 17:17:21.471509560 +0300
@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 1999,2000,2001,2002,2003 Free Software Foundation, Inc.
+ *  Copyright (C) 1999,2000,2001,2002,2003,2005 Free Software Foundation, Inc.
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -219,11 +219,11 @@
  * 31          24         19   16                 7           0
  * ------------------------------------------------------------
  * |             | |B| |A|       | |   |1|0|E|W|A|            |
- * | BASE 31..24 |G|/|0|V| LIMIT |P|DPL|  TYPE   | BASE 23:16 |
+ * | BASE 31..24 |G|/|L|V| LIMIT |P|DPL|  TYPE   | BASE 23:16 |  4
  * |             | |D| |L| 19..16| |   |1|1|C|R|A|            |
  * ------------------------------------------------------------
  * |                             |                            |
- * |        BASE 15..0           |       LIMIT 15..0          |
+ * |        BASE 15..0           |       LIMIT 15..0          |  0
  * |                             |                            |
  * ------------------------------------------------------------
  *
@@ -236,19 +236,31 @@
        .word   0, 0
        .byte   0, 0, 0, 0
 
-       /* code segment */
+       /* -- code segment --
+        * base = 0x00000000, limit = 0xFFFFF (4 KiB Granularity), present
+        * type = 32bit code execute/read, DPL = 0
+        */
        .word   0xFFFF, 0
        .byte   0, 0x9A, 0xCF, 0
 
-       /* data segment */
+       /* -- data segment --
+        * base = 0x00000000, limit 0xFFFFF (4 KiB Granularity), present
+        * type = 32 bit data read/write, DPL = 0 
+        */
        .word   0xFFFF, 0
        .byte   0, 0x92, 0xCF, 0
 
-       /* 16 bit real mode CS */
+       /* -- 16 bit real mode CS --
+        * base = 0x00000000, limit 0x0FFFF (1 B Granularity), present
+        * type = 16 bit code execute/read only/conforming, DPL = 0
+        */
        .word   0xFFFF, 0
        .byte   0, 0x9E, 0, 0
 
-       /* 16 bit real mode DS */
+       /* -- 16 bit real mode DS --
+        * base = 0x00000000, limit 0x0FFFF (1 B Granularity), present
+        * type = 16 bit data read/write, DPL = 0
+        */
        .word   0xFFFF, 0
        .byte   0, 0x92, 0, 0
 
@@ -1594,3 +1606,414 @@
        popl    %ebx
        popl    %ebp
        ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_controller_info (struct grub_vbe_info_block 
*controller_info)
+ *
+ * Register allocations for parameters:
+ * %eax                *controller_info
+ */
+FUNCTION(grub_vbe_get_controller_info)
+       pushl   %ebp
+       pushl   %edi
+
+       movw    %ax, %di                /* store *controller_info to edx:di */
+       xorw    %ax, %ax
+       shrl    $4, %eax
+       mov     %eax, %edx              /* prot_to_real destroys %eax */
+       
+       call    prot_to_real
+       .code16
+
+       pushw   %es
+
+       movw    %dx, %es                /* *controller_info is now on es:di */
+       movw    $0x4f00, %ax
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       popw    %es
+
+       DATA32 call     real_to_prot
+       .code32
+
+       movl    %edx, %eax
+       andl    $0x0FFFF, %eax          /* return value in %eax */
+       
+       popl    %edi
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_mode_info (grub_uint32_t mode,
+ *                                          struct grub_vbe_mode_info_block 
*mode_info)
+ *
+ * Register allocations for parameters:
+ * %eax                mode
+ * %edx                *mode_info
+ */
+FUNCTION(grub_vbe_get_mode_info)
+       pushl   %ebp
+       pushl   %edi
+
+       movl    %eax, %ecx              /* store mode number to %ecx */
+
+       movw    %dx, %di                /* store *mode_info to edx:di*/
+       xorw    %dx, %dx
+       shrl    $4, %edx
+
+       call    prot_to_real
+       .code16
+
+       pushw   %es
+
+       movw    %dx, %es                /* *mode_info is now on es:di */
+       movw    $0x4f01, %ax
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       popw    %es
+
+       DATA32 call     real_to_prot
+       .code32
+
+       movl    %edx, %eax
+       andl    $0x0FFFF, %eax          /* return value in %eax */
+
+       popl    %edi
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_set_mode (grub_uint32_t mode,
+ *                                     struct grub_vbe_crtc_info_block 
*crtc_info)
+ *
+ * Register allocations for parameters:
+ * %eax                mode
+ * %edx                *crtc_info
+ */
+FUNCTION(grub_vbe_set_mode)
+       pushl   %ebp
+       pushl   %ebx
+
+       movl    %eax, %ebx              /* store mode in ebx */
+
+       movw    %dx, %di                /* store *crtc_info to edx:di*/
+       xorw    %dx, %dx
+       shrl    $4, %edx
+
+       call    prot_to_real
+       .code16
+
+       pushw   %es
+
+       movw    %dx, %es                /* *crtc_info is now on es:di */
+
+       movw    $0x4f02, %ax
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       popw    %es
+
+       DATA32 call     real_to_prot
+       .code32
+       
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_mode (grub_uint32_t *mode)
+ *
+ * Register allocations for parameters:
+ * %eax                *mode
+ */
+FUNCTION(grub_vbe_get_mode)
+       pushl   %ebp
+       pushl   %ebx
+       pushl   %eax                    /* push *mode to stack */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f03, %ax
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+
+       popl    %edi                    /* pops *mode from stack to %edi */
+       andl    $0xFFFF, %ebx
+       movl    %ebx, (%edi)
+
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_set_memory_window (grub_uint32_t window,
+ *                                              grub_uint32_t position);
+ *
+ * Register allocations for parameters:
+ * %eax                window
+ * %edx                position
+ */
+FUNCTION(grub_vbe_set_memory_window)
+       pushl   %ebp
+       pushl   %ebx
+
+       movl    %eax, %ebx
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f05, %ax
+       andw    $0x00ff, %bx            /* BL = window, BH = 0, Set memory 
window */
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+       
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_memory_window (grub_uint32_t window,
+ *                                              grub_uint32_t *position);
+ *
+ * Register allocations for parameters:
+ * %eax                window
+ * %edx                *position
+ */
+FUNCTION(grub_vbe_get_memory_window)
+       pushl   %ebp
+       pushl   %ebx
+       pushl   %edx                    /* push *position to stack */
+
+       movl    %eax, %ebx              /* store window in ebx */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f05, %ax
+       andw    $0x00ff, %bx            /* BL = window */
+       orw     $0x0100, %bx            /* BH = 1, Get memory window */
+       int     $0x10
+
+       movw    %ax, %bx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+
+       popl    %edi                    /* pops *position from stack to %edi */
+       andl    $0xFFFF, %edx
+       movl    %edx, (%edi)            /* return position to caller */
+
+       movw    %bx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_set_scanline_length (grub_uint32_t length)
+ *
+ * Register allocations for parameters:
+ * %eax                length
+ */
+FUNCTION(grub_vbe_set_scanline_length)
+       pushl   %ebp
+       pushl   %ebx
+
+       movl    %eax, %ecx              /* store length in ecx */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f06, %ax
+       movw    $0x0002, %bx            /* BL = 2, Set Scan Line in Bytes */
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+       
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_scanline_length (grub_uint32_t *length)
+ *
+ * Register allocations for parameters:
+ * %eax                *length
+ */
+FUNCTION(grub_vbe_get_scanline_length)
+       pushl   %ebp
+       pushl   %ebx
+       pushl   %edx                    /* push *length to stack */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f06, %ax
+       movw    $0x0001, %bx            /* BL = 1, Get Scan Line Length (in 
bytes) */
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+
+       popl    %edi                    /* pops *length from stack to %edi */
+       andl    $0xFFFF, %ebx
+       movl    %ebx, (%edi)            /* return length to caller */
+
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_set_display_start (grub_uint32_t x,
+ *                                              grub_uint32_t y)
+ *
+ * Register allocations for parameters:
+ * %eax                x
+ * %edx                y
+ */
+FUNCTION(grub_vbe_set_display_start)
+       pushl   %ebp
+       pushl   %ebx
+
+       movl    %eax, %ecx              /* store x in ecx */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f07, %ax
+       movw    $0x0080, %bx            /* BL = 80h, Set Display Start during 
Vertical Retrace */
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+       
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_get_display_start (grub_uint32_t *x,
+ *                                              grub_uint32_t *y)
+ *
+ * Register allocations for parameters:
+ * %eax                *x
+ * %edx                *y
+ */
+FUNCTION(grub_vbe_get_display_start)
+       pushl   %ebp
+       pushl   %ebx
+       pushl   %eax                    /* push *x to stack */
+       pushl   %edx                    /* push *y to stack */
+
+       call    prot_to_real
+       .code16
+
+       movw    $0x4f07, %ax
+       movw    $0x0001, %bx            /* BL = 1, Get Display Start */
+       int     $0x10
+
+       movw    %ax, %bx                /* real_to_prot destroys %eax */
+
+       DATA32 call     real_to_prot
+       .code32
+
+       popl    %edi                    /* pops *y from stack to %edi */
+       andl    $0xFFFF, %edx
+       movl    %edx, (%edi)            /* return y-position to caller */
+
+       popl    %edi                    /* pops *x from stack to %edi */
+       andl    $0xFFFF, %ecx
+       movl    %ecx, (%edi)            /* return x-position to caller */
+
+       movw    %bx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret
+
+/*
+ * grub_vbe_status_t grub_vbe_set_palette_data (grub_uint32_t color_count,
+ *                                             grub_uint32_t start_index,
+ *                                             struct grub_vbe_palette_data 
*palette_data)
+ *
+ * Register allocations for parameters:
+ * %eax                color_count
+ * %edx                start_index
+ * %ecx                *palette_data
+ */
+FUNCTION(grub_vbe_set_palette_data)
+       pushl   %ebp
+       pushl   %ebx
+
+       movl    %eax, %ebx              /* store color_count in ebx */
+
+       movw    %cx, %di                /* store *palette_data to ecx:di */
+       xorw    %cx, %cx
+       shrl    $4, %ecx
+
+       call    prot_to_real
+       .code16
+
+       pushw   %es
+
+       movw    %cx, %es                /* *palette_data is now on es:di */
+       movw    %bx, %cx                /* color_count is now on cx */
+
+       movw    $0x4f09, %ax
+       xorw    %bx, %bx                /* BL = 0, Set Palette Data */
+       int     $0x10
+
+       movw    %ax, %dx                /* real_to_prot destroys %eax */
+
+       popw    %es
+
+       DATA32 call     real_to_prot
+       .code32
+       
+       movw    %dx, %ax
+       andl    $0xFFFF, %eax           /* return value in %eax */
+
+       popl    %ebx
+       popl    %ebp
+       ret

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