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><H1
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><A
NAME="bootloader"
></A
>C. GRUB and LILO</H1
><P
> Both <A
HREF="http://www.gnu.org/software/grub"
TARGET="_top"
>GNU GRUB</A
> and
<A
HREF="http://freshmeat.net/projects/lilo"
TARGET="_top"
>LILO</A
>
understand the real-mode kernel header format and will load
the bootsect (one sector), setup code
(<EM
>setup_sects</EM
> sectors) and
compressed kernel image (<EM
>syssize</EM
>*16 bytes) into memory.
They fill out the loader identifier (<EM
>type_of_loader</EM
>)
and try to pass appropriate parameters and options to the kernel.
After they finish their jobs, control is passed to setup code.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="grub"
></A
>C.1. GNU GRUB</H2
><P
> The following GNU GRUB program outline is based on grub-0.93.
<TABLE
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WIDTH="100%"
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COLOR="#000000"
><PRE
CLASS="programlisting"
>stage2/stage2.c:cmain()
`-- run_menu()
`-- run_script();
|-- builtin = find_command(heap);
|-- kernel_func(); // builtin->func() for command "kernel"
| `-- load_image(); // search BOOTSEC_SIGNATURE in boot.c
| /* memory from 0x100000 is populated by and in the order of
| * (bvmlinux, bbootsect, bsetup) or (vmlinux, bootsect, setup) */
|-- initrd_func(); // for command "initrd"
| `-- load_initrd();
`-- boot_func(); // for implicit command "boot"
`-- linux_boot(); // defined in stage2/asm.S
or big_linux_boot(); // not in grub/asmstub.c!
// In stage2/asm.S
linux_boot:
/* copy kernel */
move system code from 0x100000 to 0x10000 (linux_text_len bytes);
big_linux_boot:
/* copy the real mode part */
EBX = linux_data_real_addr;
move setup code from linux_data_tmp_addr (0x100000+text_len)
to linux_data_real_addr (0x9100 bytes);
/* change %ebx to the segment address */
linux_setup_seg = (EBX >> 4) + 0x20;
/* XXX new stack pointer in safe area for calling functions */
ESP = 0x4000;
stop_floppy();
/* final setup for linux boot */
prot_to_real();
cli;
SS:ESP = BX:9000;
DS = ES = FS = GS = BX;
/* jump to start, i.e. ljmp linux_setup_seg:0
* Note that linux_setup_seg is just changed to BX. */
.byte 0xea
.word 0
linux_setup_seg:
.word 0
</PRE
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>
</P
><P
> Refer to "<B
CLASS="command"
>info grub</B
>" for GRUB manual.
</P
><P
> One
<A
HREF="http://mail.gnu.org/archive/html/bug-grub/2003-03/msg00030.html"
TARGET="_top"
> reported GNU GRUB bug</A
> should be noted if you are
porting grub-0.93 and making changes to <EM
>bsetup</EM
>.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="lilo"
></A
>C.2. LILO</H2
><P
> Unlike GRUB, LILO does not check the configuration file
when booting system.
Tricks happen when <B
CLASS="command"
>lilo</B
> is invoked from terminal.
</P
><P
> The following LILO program outline is based on lilo-22.5.8.
<TABLE
BORDER="0"
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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>lilo.c:main()
|-- cfg_open(config_file);
|-- cfg_parse(cf_options);
|-- bsect_open(boot_dev, map_file, install, delay, timeout);
| |-- open_bsect(boot_dev);
| `-- map_create(map_file);
|-- cfg_parse(cf_top)
| `-- cfg_do_set();
| `-- do_image(); // walk->action for "image=" section
| |-- cfg_parse(cf_image) -> cfg_do_set();
| |-- bsect_common(&descr, 1);
| | |-- map_begin_section();
| | |-- map_add_sector(fallback_buf);
| | `-- map_add_sector(options);
| |-- boot_image(name, &descr) or boot_device(name, range, &descr);
| | |-- int fd = geo_open(&descr, name, O_RDONLY);
| | | read(fd, &buff, SECTOR_SIZE);
| | | map_add(&geo, 0, image_sectors);
| | | map_end_section(&descr->start, setup_sects+2+1);
| | | /* two sectors created in bsect_common(),
| | | * another one sector for bootsect */
| | | geo_close(&geo);
| | `-- fd = geo_open(&descr, initrd, O_RDONLY);
| | map_begin_section();
| | map_add(&geo, 0, initrd_sectors);
| | map_end_section(&descr->initrd,0);
| | geo_close(&geo);
| `-- bsect_done(name, &descr);
`-- bsect_update(backup_file, force_backup, 0); // update boot sector
|-- make_backup();
|-- map_begin_section();
| map_add_sector(table);
| map_write(&param2, keytab, 0, 0);
| map_close(&param2, here2);
|-- // ... perform the relocation of the boot sector
|-- // ... setup bsect_wr to correct place
|-- write(fd, bsect_wr, SECTOR_SIZE);
`-- close(fd);</PRE
></FONT
></TD
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>
<EM
>map_add(), map_add_sector()</EM
> and
<EM
>map_add_zero()</EM
> may call
<EM
>map_register()</EM
> to complete their jobs,
while <EM
>map_register()</EM
> will keep a list for
all (CX, DX, AL) triplets (data structure SECTOR_ADDR) used to
identify all registered sectors.
</P
><P
> LILO runs <TT
CLASS="filename"
>first.S</TT
> and <TT
CLASS="filename"
>second.S</TT
>
to boot a system.
It calls <EM
>second.S:doboot()</EM
> to load map file,
bootsect and setup code.
Then it calls <EM
>lfile()</EM
> to load the system code,
calls <EM
>launch2() -> launch() -> cl_wait() -> start_setup()
-> start_setup2()</EM
> and finnaly executes
"jmpi 0,SETUPSEG" instruction to run setup code.
</P
><P
> Refer to "<B
CLASS="command"
>man lilo</B
>" and
"<B
CLASS="command"
>man lilo.conf</B
>" for LILO details.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="bootloader_ref"
></A
>C.3. Reference</H2
><P
> <P
></P
><UL
><LI
><P
> <A
HREF="http://www.gnu.org/software/grub/"
TARGET="_top"
>GNU GRUB</A
>
</P
></LI
><LI
><P
> <A
HREF="http://www.openbg.net/sto/os/xml/grub.html"
TARGET="_top"
>GRUB Tutorial</A
>
</P
></LI
><LI
><P
> <A
HREF="http://freshmeat.net/projects/lilo"
TARGET="_top"
>LILO (freshmeat.net)</A
>
</P
></LI
><LI
><P
> <A
HREF="http://www.tldp.org/HOWTO/HOWTO-INDEX/os.html#OSBOOT"
TARGET="_top"
> LDP HOWTO-INDEX: Boot Loaders and Booting the OS</A
>
</P
></LI
></UL
>
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