/* SPDX-License-Identifier: GPL-2.0 */
/*
* 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/init.h>
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page_types.h>
#include <asm/boot.h>
#include <asm/asm-offsets.h>
#include <asm/bootparam.h>
/*
* These symbols needed to be marked as .hidden to prevent the BFD linker from
* generating R_386_32 (rather than R_386_RELATIVE) relocations for them when
* the 32-bit compressed kernel is linked as PIE. This is no longer necessary,
* but it doesn't hurt to keep them .hidden.
*/
.hidden _bss
.hidden _ebss
.hidden _end
__HEAD
SYM_FUNC_START(startup_32)
cld
cli
/*
* Calculate the delta between where we were compiled to run
* at and where we were actually loaded at. This can only be done
* with a short local call on x86. Nothing else will tell us what
* address we are running at. The reserved chunk of the real-mode
* data at 0x1e4 (defined as a scratch field) are used as the stack
* for this calculation. Only 4 bytes are needed.
*/
leal (BP_scratch+4)(%esi), %esp
call 1f
1: popl %edx
addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx
/* Load new GDT */
leal gdt@GOTOFF(%edx), %eax
movl %eax, 2(%eax)
lgdt (%eax)
/* Load segment registers with our descriptors */
movl $__BOOT_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
/*
* %edx contains the address we are loaded at by the boot loader (plus the
* offset to the GOT). The below code calculates %ebx to be the address where
* we should move the kernel image temporarily for safe in-place decompression
* (again, plus the offset to the GOT).
*
* %ebp is calculated to be the address that the kernel will be decompressed to.
*/
#ifdef CONFIG_RELOCATABLE
leal startup_32@GOTOFF(%edx), %ebx
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
notl %eax
andl %eax, %ebx
cmpl $LOAD_PHYSICAL_ADDR, %ebx
jae 1f
#endif
movl $LOAD_PHYSICAL_ADDR, %ebx
1:
movl %ebx, %ebp // Save the output address for later
/* Target address to relocate to for decompression */
addl BP_init_size(%esi), %ebx
subl $_end@GOTOFF, %ebx
/* Set up the stack */
leal boot_stack_end@GOTOFF(%ebx), %esp
/* Zero EFLAGS */
pushl $0
popfl
/*
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
pushl %esi
leal (_bss@GOTOFF-4)(%edx), %esi
leal (_bss@GOTOFF-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
shrl $2, %ecx
std
rep movsl
cld
popl %esi
/*
* The GDT may get overwritten either during the copy we just did or
* during extract_kernel below. To avoid any issues, repoint the GDTR
* to the new copy of the GDT.
*/
leal gdt@GOTOFF(%ebx), %eax
movl %eax, 2(%eax)
lgdt (%eax)
/*
* Jump to the relocated address.
*/
leal .Lrelocated@GOTOFF(%ebx), %eax
jmp *%eax
SYM_FUNC_END(startup_32)
.text
SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/*
* Clear BSS (stack is currently empty)
*/
xorl %eax, %eax
leal _bss@GOTOFF(%ebx), %edi
leal _ebss@GOTOFF(%ebx), %ecx
subl %edi, %ecx
shrl $2, %ecx
rep stosl
/*
* Do the extraction, and jump to the new kernel..
*/
/* push arguments for extract_kernel: */
pushl %ebp
/* output address */
pushl %esi
/* real mode pointer */
call extract_kernel
/* returns kernel entry point in %eax */
addl $24, %esp
/*
* Jump to the extracted kernel.
*/
xorl %ebx, %ebx
jmp *%eax
SYM_FUNC_END(.Lrelocated)
.
data
.balign 8
SYM_DATA_START_LOCAL(gdt)
.
word gdt_end - gdt - 1
.long 0
.
word 0
.quad 0x0000000000000000
/* Reserved */
.quad 0x00cf9a000000ffff
/* __KERNEL_CS */
.quad 0x00cf92000000ffff
/* __KERNEL_DS */
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
/*
* Stack and heap for uncompression
*/
.bss
.balign 4
boot_stack:
.fill BOOT_STACK_SIZE, 1, 0
boot_stack_end:
