4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
8 * head.S contains the 32-bit startup code.
10 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
11 * the page directory will exist. The startup code will be overwritten by
12 * the page directory. [According to comments etc elsewhere on a compressed
13 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
15 * Page 0 is deliberately kept safe, since System Management Mode code in
16 * laptops may need to access the BIOS data stored there. This is also
17 * useful for future device drivers that either access the BIOS via VM86
22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
26 #include <linux/linkage.h>
27 #include <asm/segment.h>
35 movl $(__BOOT_DS),%eax
43 1: incl %eax # check that A20 really IS enabled
44 movl %eax,0x000000 # loop forever if it isn't
49 * Initialize eflags. Some BIOS's leave bits like NT set. This would
50 * confuse the debugger if this code is traced.
51 * XXX - best to initialize before switching to protected mode.
66 * Do the decompression, and jump to the new kernel..
68 subl $16,%esp # place for structure on the stack
70 pushl %esi # real mode pointer as second arg
71 pushl %eax # address of structure as first arg
72 call decompress_kernel
75 popl %esi # discard address
76 popl %esi # real mode pointer
78 ljmp $(__BOOT_CS), $__PHYSICAL_START
81 * We come here, if we were loaded high.
82 * We need to move the move-in-place routine down to 0x1000
83 * and then start it with the buffer addresses in registers,
84 * which we got from the stack.
87 movl $move_routine_start,%esi
89 movl $move_routine_end,%ecx
97 popl %esi # discard the address
98 popl %ebx # real mode pointer
99 popl %esi # low_buffer_start
101 popl %edx # high_buffer_start
103 movl $__PHYSICAL_START,%edi
104 cli # make sure we don't get interrupted
105 ljmp $(__BOOT_CS), $0x1000 # and jump to the move routine
108 * Routine (template) for moving the decompressed kernel in place,
109 * if we were high loaded. This _must_ PIC-code !
121 movl %eax,%ecx # NOTE: rep movsb won't move if %ecx == 0
126 movl %ebx,%esi # Restore setup pointer
128 ljmp $(__BOOT_CS), $__PHYSICAL_START