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225 lines
5.6 KiB
225 lines
5.6 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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/* |
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* linux/boot/head.S |
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* |
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* Copyright (C) 1991, 1992, 1993 Linus Torvalds |
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*/ |
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/* |
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* head.S contains the 32-bit startup code. |
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* |
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* NOTE!!! Startup happens at absolute address 0x00001000, which is also where |
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* the page directory will exist. The startup code will be overwritten by |
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* the page directory. [According to comments etc elsewhere on a compressed |
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* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] |
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* |
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* Page 0 is deliberately kept safe, since System Management Mode code in |
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* laptops may need to access the BIOS data stored there. This is also |
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* useful for future device drivers that either access the BIOS via VM86 |
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* mode. |
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*/ |
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/* |
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* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 |
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*/ |
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.text |
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#include <linux/init.h> |
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#include <linux/linkage.h> |
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#include <asm/segment.h> |
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#include <asm/page_types.h> |
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#include <asm/boot.h> |
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#include <asm/asm-offsets.h> |
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#include <asm/bootparam.h> |
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/* |
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* These symbols needed to be marked as .hidden to prevent the BFD linker from |
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* generating R_386_32 (rather than R_386_RELATIVE) relocations for them when |
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* the 32-bit compressed kernel is linked as PIE. This is no longer necessary, |
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* but it doesn't hurt to keep them .hidden. |
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*/ |
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.hidden _bss |
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.hidden _ebss |
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.hidden _end |
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__HEAD |
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SYM_FUNC_START(startup_32) |
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cld |
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cli |
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/* |
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* Calculate the delta between where we were compiled to run |
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* at and where we were actually loaded at. This can only be done |
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* with a short local call on x86. Nothing else will tell us what |
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* address we are running at. The reserved chunk of the real-mode |
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* data at 0x1e4 (defined as a scratch field) are used as the stack |
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* for this calculation. Only 4 bytes are needed. |
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*/ |
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leal (BP_scratch+4)(%esi), %esp |
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call 1f |
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1: popl %edx |
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addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %edx |
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/* Load new GDT */ |
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leal gdt@GOTOFF(%edx), %eax |
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movl %eax, 2(%eax) |
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lgdt (%eax) |
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/* Load segment registers with our descriptors */ |
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movl $__BOOT_DS, %eax |
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movl %eax, %ds |
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movl %eax, %es |
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movl %eax, %fs |
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movl %eax, %gs |
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movl %eax, %ss |
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/* |
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* %edx contains the address we are loaded at by the boot loader (plus the |
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* offset to the GOT). The below code calculates %ebx to be the address where |
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* we should move the kernel image temporarily for safe in-place decompression |
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* (again, plus the offset to the GOT). |
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* |
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* %ebp is calculated to be the address that the kernel will be decompressed to. |
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*/ |
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#ifdef CONFIG_RELOCATABLE |
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leal startup_32@GOTOFF(%edx), %ebx |
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#ifdef CONFIG_EFI_STUB |
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/* |
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* If we were loaded via the EFI LoadImage service, startup_32() will be at an |
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* offset to the start of the space allocated for the image. efi_pe_entry() will |
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* set up image_offset to tell us where the image actually starts, so that we |
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* can use the full available buffer. |
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* image_offset = startup_32 - image_base |
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* Otherwise image_offset will be zero and has no effect on the calculations. |
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*/ |
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subl image_offset@GOTOFF(%edx), %ebx |
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#endif |
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movl BP_kernel_alignment(%esi), %eax |
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decl %eax |
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addl %eax, %ebx |
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notl %eax |
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andl %eax, %ebx |
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cmpl $LOAD_PHYSICAL_ADDR, %ebx |
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jae 1f |
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#endif |
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movl $LOAD_PHYSICAL_ADDR, %ebx |
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1: |
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movl %ebx, %ebp // Save the output address for later |
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/* Target address to relocate to for decompression */ |
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addl BP_init_size(%esi), %ebx |
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subl $_end@GOTOFF, %ebx |
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/* Set up the stack */ |
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leal boot_stack_end@GOTOFF(%ebx), %esp |
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/* Zero EFLAGS */ |
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pushl $0 |
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popfl |
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/* |
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* Copy the compressed kernel to the end of our buffer |
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* where decompression in place becomes safe. |
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*/ |
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pushl %esi |
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leal (_bss@GOTOFF-4)(%edx), %esi |
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leal (_bss@GOTOFF-4)(%ebx), %edi |
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movl $(_bss - startup_32), %ecx |
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shrl $2, %ecx |
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std |
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rep movsl |
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cld |
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popl %esi |
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/* |
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* The GDT may get overwritten either during the copy we just did or |
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* during extract_kernel below. To avoid any issues, repoint the GDTR |
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* to the new copy of the GDT. |
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*/ |
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leal gdt@GOTOFF(%ebx), %eax |
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movl %eax, 2(%eax) |
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lgdt (%eax) |
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/* |
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* Jump to the relocated address. |
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*/ |
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leal .Lrelocated@GOTOFF(%ebx), %eax |
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jmp *%eax |
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SYM_FUNC_END(startup_32) |
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#ifdef CONFIG_EFI_STUB |
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SYM_FUNC_START(efi32_stub_entry) |
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SYM_FUNC_START_ALIAS(efi_stub_entry) |
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add $0x4, %esp |
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movl 8(%esp), %esi /* save boot_params pointer */ |
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call efi_main |
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/* efi_main returns the possibly relocated address of startup_32 */ |
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jmp *%eax |
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SYM_FUNC_END(efi32_stub_entry) |
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SYM_FUNC_END_ALIAS(efi_stub_entry) |
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#endif |
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.text |
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SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) |
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/* |
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* Clear BSS (stack is currently empty) |
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*/ |
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xorl %eax, %eax |
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leal _bss@GOTOFF(%ebx), %edi |
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leal _ebss@GOTOFF(%ebx), %ecx |
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subl %edi, %ecx |
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shrl $2, %ecx |
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rep stosl |
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/* |
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* Do the extraction, and jump to the new kernel.. |
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*/ |
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/* push arguments for extract_kernel: */ |
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pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */ |
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pushl %ebp /* output address */ |
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pushl input_len@GOTOFF(%ebx) /* input_len */ |
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leal input_data@GOTOFF(%ebx), %eax |
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pushl %eax /* input_data */ |
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leal boot_heap@GOTOFF(%ebx), %eax |
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pushl %eax /* heap area */ |
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pushl %esi /* real mode pointer */ |
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call extract_kernel /* returns kernel location in %eax */ |
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addl $24, %esp |
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/* |
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* Jump to the extracted kernel. |
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*/ |
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xorl %ebx, %ebx |
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jmp *%eax |
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SYM_FUNC_END(.Lrelocated) |
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.data |
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.balign 8 |
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SYM_DATA_START_LOCAL(gdt) |
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.word gdt_end - gdt - 1 |
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.long 0 |
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.word 0 |
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.quad 0x0000000000000000 /* Reserved */ |
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.quad 0x00cf9a000000ffff /* __KERNEL_CS */ |
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.quad 0x00cf92000000ffff /* __KERNEL_DS */ |
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SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) |
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#ifdef CONFIG_EFI_STUB |
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SYM_DATA(image_offset, .long 0) |
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#endif |
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/* |
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* Stack and heap for uncompression |
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*/ |
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.bss |
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.balign 4 |
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boot_heap: |
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.fill BOOT_HEAP_SIZE, 1, 0 |
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boot_stack: |
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.fill BOOT_STACK_SIZE, 1, 0 |
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boot_stack_end:
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