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[lkrnprefix] Make gPXE .lkrn images conform to the zImage 2.07 format
This commit is contained in:
Stefan Hajnoczi
Michael Brown
parent
ce51128534
commit
1719b105cd
@ -10,8 +10,8 @@
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Description:
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This is just a little bit of code and data that can get prepended
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to an Etherboot ROM image in order to allow LILO to load the
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result as if it were a Linux kernel image.
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to a ROM image in order to allow bootloaders to load the result
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as if it were a Linux kernel image.
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A real Linux kernel image consists of a one-sector boot loader
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(to load the image from a floppy disk), followed a few sectors
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@ -21,19 +21,16 @@
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contains some other parameters that aren't interesting in this
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case.
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When LILO loads the sectors that comprise a kernel image, it doesn't
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execute the code in the first sector (since that code would try to
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load the image from a floppy disk.) The code in the first sector
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below doesn't expect to get executed (and prints an error message
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if it ever -is- executed.) LILO's only interested in knowing the
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number of setup sectors advertised in the table (at offset 497 in
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the first sector.)
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When a bootloader loads the sectors that comprise a kernel image,
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it doesn't execute the code in the first sector (since that code
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would try to load the image from a floppy disk.) The code in the
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first sector below doesn't expect to get executed (and prints an
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error message if it ever -is- executed.)
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Etherboot doesn't require much in the way of setup code.
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Historically, the Linux kernel required at least 4 sectors of
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setup code. Current versions of LILO look at the byte at
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offset 497 in the first sector to indicate how many sectors
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of setup code are contained in the image.
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We don't require much in the way of setup code. Historically, the
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Linux kernel required at least 4 sectors of setup code.
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Therefore, at least 4 sectors must be present even though we don't
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use them.
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*/
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@ -85,15 +82,25 @@ why: .ascii "This image cannot be loaded from a floppy disk.\r\n"
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why_end:
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/*
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The following header is documented in the Linux source code at
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Documentation/i386/boot.txt
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*/
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.org 497
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setup_sects:
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.byte SETUPSECS
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root_flags:
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.word 0
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syssize:
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.word _load_size_pgh - PREFIXPGH
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swap_dev:
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.word 0
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.long _load_size_pgh - PREFIXPGH
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.section ".zinfo.fixup", "a" /* Compressor fixup information */
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.ascii "SUBL"
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.long syssize
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.long 16
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.long 0
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.previous
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ram_size:
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.word 0
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vid_mode:
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@ -102,44 +109,86 @@ root_dev:
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.word 0
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boot_flag:
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.word 0xAA55
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.org 512
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.section ".zinfo.fixup", "a" /* Compressor fixup information */
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.ascii "SUBW"
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.long syssize
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.long 16
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jump:
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jmp setup_code
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header:
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.byte 'H', 'd', 'r', 'S'
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version:
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.word 0x0207 /* 2.07 */
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realmode_swtch:
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.long 0
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.previous
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/*
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We're now at the beginning of the second sector of the image -
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where the setup code goes.
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start_sys:
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.word 0
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kernel_version:
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.word 0
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type_of_loader:
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.byte 0
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loadflags:
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.byte 0
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setup_move_size:
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.word 0
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code32_start:
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.long 0
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ramdisk_image:
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.long 0
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ramdisk_size:
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.long 0
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bootsect_kludge:
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.long 0
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heap_end_ptr:
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.word 0
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pad1:
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.word 0
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cmd_line_ptr:
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.long 0
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initrd_addr_max:
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.long 0
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kernel_alignment:
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.long 0
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relocatable_kernel:
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.byte 0
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pad2:
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.byte 0, 0, 0
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cmdline_size:
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.long 0
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hardware_subarch:
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.long 0
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hardware_subarch_data:
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.byte 0, 0, 0, 0, 0, 0, 0, 0
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We don't need to do too much setup for Etherboot.
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/*
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We don't need to do too much setup.
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This code gets loaded at SETUPSEG:0. It wants to start
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executing the Etherboot image that's loaded at SYSSEG:0 and
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executing the image that's loaded at SYSSEG:0 and
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whose entry point is SYSSEG:0.
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*/
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setup_code:
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/* Etherboot expects to be contiguous in memory once loaded.
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* LILO doesn't do this, but since we don't need any
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* information that's left in the prefix, it doesn't matter:
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* we just have to ensure that %cs:0000 is where the start of
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* the Etherboot image *would* be.
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/* We expect to be contiguous in memory once loaded. The Linux image
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* boot process requires that setup code is loaded separately from
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* "non-real code". Since we don't need any information that's left
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* in the prefix, it doesn't matter: we just have to ensure that
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* %cs:0000 is where the start of the image *would* be.
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*/
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ljmp $(SYSSEG-(PREFIXSIZE/16)), $run_etherboot
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ljmp $(SYSSEG-(PREFIXSIZE/16)), $run_gpxe
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.org PREFIXSIZE
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/*
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We're now at the beginning of the kernel proper.
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*/
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run_etherboot:
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run_gpxe:
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/* Set up stack just below 0x7c00 */
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xorw %ax, %ax
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movw %ax, %ss
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movw $0x7c00, %sp
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call install
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/* Set up real-mode stack */
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movw %bx, %ss
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movw $_estack16, %sp
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/* Jump to .text16 segment */
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pushw %ax
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pushw $1f
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