/* 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 #include #include #include #include #include #include /* * 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 #ifdef CONFIG_EFI_STUB /* * If we were loaded via the EFI LoadImage service, startup_32() will be at an * offset to the start of the space allocated for the image. efi_pe_entry() will * set up image_offset to tell us where the image actually starts, so that we * can use the full available buffer. * image_offset = startup_32 - image_base * Otherwise image_offset will be zero and has no effect on the calculations. */ subl image_offset@GOTOFF(%edx), %ebx #endif 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) #ifdef CONFIG_EFI_STUB SYM_FUNC_START(efi32_stub_entry) add $0x4, %esp movl 8(%esp), %esi /* save boot_params pointer */ call efi_main /* efi_main returns the possibly relocated address of startup_32 */ jmp *%eax SYM_FUNC_END(efi32_stub_entry) SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry) #endif .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 output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */ pushl %ebp /* output address */ pushl input_len@GOTOFF(%ebx) /* input_len */ leal input_data@GOTOFF(%ebx), %eax pushl %eax /* input_data */ leal boot_heap@GOTOFF(%ebx), %eax pushl %eax /* heap area */ pushl %esi /* real mode pointer */ call extract_kernel /* returns kernel location 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) #ifdef CONFIG_EFI_STUB SYM_DATA(image_offset, .long 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: