/*
   *  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>
  
  /*
   * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
   * relocation to get the symbol address in PIC.  When the compressed x86
   * kernel isn't built as PIC, the linker optimizes R_386_GOT32X
   * relocations to their fixed symbol addresses.  However, when the
   * compressed x86 kernel is loaded at a different address, it leads
   * to the following load failure:
   *
   *   Failed to allocate space for phdrs
   *
   * during the decompression stage.
   *
   * If the compressed x86 kernel is relocatable at run-time, it should be
   * compiled with -fPIE, instead of -fPIC, if possible and should be built as
   * Position Independent Executable (PIE) so that linker won't optimize
   * R_386_GOT32X relocation to its fixed symbol address.  Older
   * linkers generate R_386_32 relocations against locally defined symbols,
   * _bss, _ebss, _got and _egot, in PIE.  It isn't wrong, just less
   * optimal than R_386_RELATIVE.  But the x86 kernel fails to properly handle
   * R_386_32 relocations when relocating the kernel.  To generate
   * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
   * hidden:
   */
  	.hidden _bss
  	.hidden _ebss
  	.hidden _got
  	.hidden _egot
  
  	__HEAD
  ENTRY(startup_32)
  #ifdef CONFIG_EFI_STUB
  	jmp	preferred_addr
  
  	/*
  	 * We don't need the return address, so set up the stack so
  	 * efi_main() can find its arguments.
  	 */
  ENTRY(efi_pe_entry)
  	add	$0x4, %esp
  
  	call	1f
  1:	popl	%esi
  	subl	$1b, %esi
  
  	popl	%ecx
  	movl	%ecx, efi32_config(%esi)	/* Handle */
  	popl	%ecx
  	movl	%ecx, efi32_config+8(%esi)	/* EFI System table pointer */
  
  	/* Relocate efi_config->call() */
  	leal	efi32_config(%esi), %eax
  	add	%esi, 88(%eax)
  	pushl	%eax
  
  	call	make_boot_params
  	cmpl	$0, %eax
  	je	fail
  	movl	%esi, BP_code32_start(%eax)
  	popl	%ecx
  	pushl	%eax
  	pushl	%ecx
  	jmp	2f		/* Skip efi_config initialization */
  
  ENTRY(efi32_stub_entry)
  	add	$0x4, %esp
  	popl	%ecx
  	popl	%edx
  
  	call	1f
  1:	popl	%esi
  	subl	$1b, %esi
  
  	movl	%ecx, efi32_config(%esi)	/* Handle */
  	movl	%edx, efi32_config+8(%esi)	/* EFI System table pointer */
  
  	/* Relocate efi_config->call() */
  	leal	efi32_config(%esi), %eax
  	add	%esi, 88(%eax)
  	pushl	%eax
  2:
  	call	efi_main
  	cmpl	$0, %eax
  	movl	%eax, %esi
  	jne	2f
  fail:
  	/* EFI init failed, so hang. */
  	hlt
  	jmp	fail
  2:
  	movl	BP_code32_start(%esi), %eax
  	leal	preferred_addr(%eax), %eax
  	jmp	*%eax
  
  preferred_addr:
  #endif
  	cld
  	/*
  	 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
  	 * us to not reload segments
  	 */
  	testb	$KEEP_SEGMENTS, BP_loadflags(%esi)
  	jnz	1f
  
  	cli
  	movl	$__BOOT_DS, %eax
  	movl	%eax, %ds
  	movl	%eax, %es
  	movl	%eax, %fs
  	movl	%eax, %gs
  	movl	%eax, %ss
  1:
  
  /*
   * 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	%ebp
  	subl	$1b, %ebp
  
  /*
   * %ebp contains the address we are loaded at by the boot loader and %ebx
   * contains the address where we should move the kernel image temporarily
   * for safe in-place decompression.
   */
  
  #ifdef CONFIG_RELOCATABLE
  	movl	%ebp, %ebx
  	movl	BP_kernel_alignment(%esi), %eax
  	decl	%eax
  	addl    %eax, %ebx
  	notl	%eax
  	andl    %eax, %ebx
  	cmpl	$LOAD_PHYSICAL_ADDR, %ebx
  	jge	1f
  #endif
  	movl	$LOAD_PHYSICAL_ADDR, %ebx
  1:
  
  	/* Target address to relocate to for decompression */
  	addl	$z_extract_offset, %ebx
  
  	/* Set up the stack */
  	leal	boot_stack_end(%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-4)(%ebp), %esi
  	leal	(_bss-4)(%ebx), %edi
  	movl	$(_bss - startup_32), %ecx
  	shrl	$2, %ecx
  	std
  	rep	movsl
  	cld
  	popl	%esi
  
  /*
   * Jump to the relocated address.
   */
  	leal	relocated(%ebx), %eax
  	jmp	*%eax
  ENDPROC(startup_32)
  
  	.text
  relocated:
  
  /*
   * Clear BSS (stack is currently empty)
   */
  	xorl	%eax, %eax
  	leal	_bss(%ebx), %edi
  	leal	_ebss(%ebx), %ecx
  	subl	%edi, %ecx
  	shrl	$2, %ecx
  	rep	stosl
  
  /*
   * Adjust our own GOT
   */
  	leal	_got(%ebx), %edx
  	leal	_egot(%ebx), %ecx
  1:
  	cmpl	%ecx, %edx
  	jae	2f
  	addl	%ebx, (%edx)
  	addl	$4, %edx
  	jmp	1b
  2:
  
  /*
   * Do the decompression, and jump to the new kernel..
   */
  				/* push arguments for decompress_kernel: */
  	pushl	$z_run_size	/* size of kernel with .bss and .brk */
  	pushl	$z_output_len	/* decompressed length, end of relocs */
  	leal	z_extract_offset_negative(%ebx), %ebp
  	pushl	%ebp		/* output address */
  	pushl	$z_input_len	/* input_len */
  	leal	input_data(%ebx), %eax
  	pushl	%eax		/* input_data */
  	leal	boot_heap(%ebx), %eax
  	pushl	%eax		/* heap area */
  	pushl	%esi		/* real mode pointer */
  	call	decompress_kernel /* returns kernel location in %eax */
  	addl	$28, %esp
  
  /*
   * Jump to the decompressed kernel.
   */
  	xorl	%ebx, %ebx
  	jmp	*%eax
  
  #ifdef CONFIG_EFI_STUB
  	.data
  efi32_config:
  	.fill 11,8,0
  	.long efi_call_phys
  	.long 0
  	.byte 0
  #endif
  
  /*
   * Stack and heap for uncompression
   */
  	.bss
  	.balign 4
  boot_heap:
  	.fill BOOT_HEAP_SIZE, 1, 0
  boot_stack:
  	.fill BOOT_STACK_SIZE, 1, 0
  boot_stack_end: