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Diffstat (limited to 'arch/i386/boot/compressed/head.S')
| -rw-r--r-- | arch/i386/boot/compressed/head.S | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/arch/i386/boot/compressed/head.S b/arch/i386/boot/compressed/head.S new file mode 100644 index 00000000000..c5e80b69e7d --- /dev/null +++ b/arch/i386/boot/compressed/head.S @@ -0,0 +1,128 @@ +/* + * linux/boot/head.S + * + * Copyright (C) 1991, 1992, 1993 Linus Torvalds + */ + +/* + * head.S contains the 32-bit startup code. + * + * NOTE!!! Startup happens at absolute address 0x00001000, which is also where + * the page directory will exist. The startup code will be overwritten by + * the page directory. [According to comments etc elsewhere on a compressed + * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] + * + * Page 0 is deliberately kept safe, since System Management Mode code in + * laptops may need to access the BIOS data stored there. This is also + * useful for future device drivers that either access the BIOS via VM86 + * mode. + */ + +/* + * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 + */ +.text + +#include <linux/linkage.h> +#include <asm/segment.h> + + .globl startup_32 + +startup_32: + cld + cli + movl $(__BOOT_DS),%eax + movl %eax,%ds + movl %eax,%es + movl %eax,%fs + movl %eax,%gs + + lss stack_start,%esp + xorl %eax,%eax +1: incl %eax # check that A20 really IS enabled + movl %eax,0x000000 # loop forever if it isn't + cmpl %eax,0x100000 + je 1b + +/* + * Initialize eflags. Some BIOS's leave bits like NT set. This would + * confuse the debugger if this code is traced. + * XXX - best to initialize before switching to protected mode. + */ + pushl $0 + popfl +/* + * Clear BSS + */ + xorl %eax,%eax + movl $_edata,%edi + movl $_end,%ecx + subl %edi,%ecx + cld + rep + stosb +/* + * Do the decompression, and jump to the new kernel.. + */ + subl $16,%esp # place for structure on the stack + movl %esp,%eax + pushl %esi # real mode pointer as second arg + pushl %eax # address of structure as first arg + call decompress_kernel + orl %eax,%eax + jnz 3f + popl %esi # discard address + popl %esi # real mode pointer + xorl %ebx,%ebx + ljmp $(__BOOT_CS), $0x100000 + +/* + * We come here, if we were loaded high. + * We need to move the move-in-place routine down to 0x1000 + * and then start it with the buffer addresses in registers, + * which we got from the stack. + */ +3: + movl $move_routine_start,%esi + movl $0x1000,%edi + movl $move_routine_end,%ecx + subl %esi,%ecx + addl $3,%ecx + shrl $2,%ecx + cld + rep + movsl + + popl %esi # discard the address + popl %ebx # real mode pointer + popl %esi # low_buffer_start + popl %ecx # lcount + popl %edx # high_buffer_start + popl %eax # hcount + movl $0x100000,%edi + cli # make sure we don't get interrupted + ljmp $(__BOOT_CS), $0x1000 # and jump to the move routine + +/* + * Routine (template) for moving the decompressed kernel in place, + * if we were high loaded. This _must_ PIC-code ! + */ +move_routine_start: + movl %ecx,%ebp + shrl $2,%ecx + rep + movsl + movl %ebp,%ecx + andl $3,%ecx + rep + movsb + movl %edx,%esi + movl %eax,%ecx # NOTE: rep movsb won't move if %ecx == 0 + addl $3,%ecx + shrl $2,%ecx + rep + movsl + movl %ebx,%esi # Restore setup pointer + xorl %ebx,%ebx + ljmp $(__BOOT_CS), $0x100000 +move_routine_end: |