/* 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 /* * 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 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 subl $1b, %edx /* Load new GDT */ leal gdt(%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 and %ebx * contains the address where we should move the kernel image temporarily * for safe in-place decompression. %ebp contains the address that the kernel * will be decompressed to. */ #ifdef CONFIG_RELOCATABLE movl %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(%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, %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)(%edx), %esi leal (_bss-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(%ebx), %eax movl %eax, 2(%eax) lgdt (%eax) /* * Jump to the relocated address. */ leal .Lrelocated(%ebx), %eax jmp *%eax SYM_FUNC_END(startup_32) #ifdef CONFIG_EFI_STUB SYM_FUNC_START(efi32_stub_entry) SYM_FUNC_START_ALIAS(efi_stub_entry) add $0x4, %esp movl 8(%esp), %esi /* save boot_params pointer */ call efi_main leal startup_32(%eax), %eax jmp *%eax SYM_FUNC_END(efi32_stub_entry) SYM_FUNC_END_ALIAS(efi_stub_entry) #endif .text SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) /* * 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 extraction, and jump to the new kernel.. */ /* push arguments for extract_kernel: */ pushl $z_output_len /* decompressed length, end of relocs */ 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 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: