1/* 2 * linux/boot/head.S 3 * 4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds 5 */ 6 7/* 8 * head.S contains the 32-bit startup code. 9 * 10 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where 11 * the page directory will exist. The startup code will be overwritten by 12 * the page directory. [According to comments etc elsewhere on a compressed 13 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] 14 * 15 * Page 0 is deliberately kept safe, since System Management Mode code in 16 * laptops may need to access the BIOS data stored there. This is also 17 * useful for future device drivers that either access the BIOS via VM86 18 * mode. 19 */ 20 21/* 22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 23 */ 24 .text 25 26#include <linux/init.h> 27#include <linux/linkage.h> 28#include <asm/segment.h> 29#include <asm/page_types.h> 30#include <asm/boot.h> 31#include <asm/asm-offsets.h> 32#include <asm/bootparam.h> 33 34/* 35 * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X 36 * relocation to get the symbol address in PIC. When the compressed x86 37 * kernel isn't built as PIC, the linker optimizes R_386_GOT32X 38 * relocations to their fixed symbol addresses. However, when the 39 * compressed x86 kernel is loaded at a different address, it leads 40 * to the following load failure: 41 * 42 * Failed to allocate space for phdrs 43 * 44 * during the decompression stage. 45 * 46 * If the compressed x86 kernel is relocatable at run-time, it should be 47 * compiled with -fPIE, instead of -fPIC, if possible and should be built as 48 * Position Independent Executable (PIE) so that linker won't optimize 49 * R_386_GOT32X relocation to its fixed symbol address. Older 50 * linkers generate R_386_32 relocations against locally defined symbols, 51 * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less 52 * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle 53 * R_386_32 relocations when relocating the kernel. To generate 54 * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as 55 * hidden: 56 */ 57 .hidden _bss 58 .hidden _ebss 59 .hidden _got 60 .hidden _egot 61 62 __HEAD 63ENTRY(startup_32) 64 cld 65 /* 66 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 67 * us to not reload segments 68 */ 69 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 70 jnz 1f 71 72 cli 73 movl $__BOOT_DS, %eax 74 movl %eax, %ds 75 movl %eax, %es 76 movl %eax, %fs 77 movl %eax, %gs 78 movl %eax, %ss 791: 80 81/* 82 * Calculate the delta between where we were compiled to run 83 * at and where we were actually loaded at. This can only be done 84 * with a short local call on x86. Nothing else will tell us what 85 * address we are running at. The reserved chunk of the real-mode 86 * data at 0x1e4 (defined as a scratch field) are used as the stack 87 * for this calculation. Only 4 bytes are needed. 88 */ 89 leal (BP_scratch+4)(%esi), %esp 90 call 1f 911: popl %ebp 92 subl $1b, %ebp 93 94/* 95 * %ebp contains the address we are loaded at by the boot loader and %ebx 96 * contains the address where we should move the kernel image temporarily 97 * for safe in-place decompression. 98 */ 99 100#ifdef CONFIG_RELOCATABLE 101 movl %ebp, %ebx 102 movl BP_kernel_alignment(%esi), %eax 103 decl %eax 104 addl %eax, %ebx 105 notl %eax 106 andl %eax, %ebx 107 cmpl $LOAD_PHYSICAL_ADDR, %ebx 108 jge 1f 109#endif 110 movl $LOAD_PHYSICAL_ADDR, %ebx 1111: 112 113 /* Target address to relocate to for decompression */ 114 movl BP_init_size(%esi), %eax 115 subl $_end, %eax 116 addl %eax, %ebx 117 118 /* Set up the stack */ 119 leal boot_stack_end(%ebx), %esp 120 121 /* Zero EFLAGS */ 122 pushl $0 123 popfl 124 125/* 126 * Copy the compressed kernel to the end of our buffer 127 * where decompression in place becomes safe. 128 */ 129 pushl %esi 130 leal (_bss-4)(%ebp), %esi 131 leal (_bss-4)(%ebx), %edi 132 movl $(_bss - startup_32), %ecx 133 shrl $2, %ecx 134 std 135 rep movsl 136 cld 137 popl %esi 138 139/* 140 * Jump to the relocated address. 141 */ 142 leal relocated(%ebx), %eax 143 jmp *%eax 144ENDPROC(startup_32) 145 146#ifdef CONFIG_EFI_STUB 147/* 148 * We don't need the return address, so set up the stack so efi_main() can find 149 * its arguments. 150 */ 151ENTRY(efi_pe_entry) 152 add $0x4, %esp 153 154 call 1f 1551: popl %esi 156 subl $1b, %esi 157 158 popl %ecx 159 movl %ecx, efi32_config(%esi) /* Handle */ 160 popl %ecx 161 movl %ecx, efi32_config+8(%esi) /* EFI System table pointer */ 162 163 /* Relocate efi_config->call() */ 164 leal efi32_config(%esi), %eax 165 add %esi, 40(%eax) 166 pushl %eax 167 168 call make_boot_params 169 cmpl $0, %eax 170 je fail 171 movl %esi, BP_code32_start(%eax) 172 popl %ecx 173 pushl %eax 174 pushl %ecx 175 jmp 2f /* Skip efi_config initialization */ 176ENDPROC(efi_pe_entry) 177 178ENTRY(efi32_stub_entry) 179 add $0x4, %esp 180 popl %ecx 181 popl %edx 182 183 call 1f 1841: popl %esi 185 subl $1b, %esi 186 187 movl %ecx, efi32_config(%esi) /* Handle */ 188 movl %edx, efi32_config+8(%esi) /* EFI System table pointer */ 189 190 /* Relocate efi_config->call() */ 191 leal efi32_config(%esi), %eax 192 add %esi, 40(%eax) 193 pushl %eax 1942: 195 call efi_main 196 cmpl $0, %eax 197 movl %eax, %esi 198 jne 2f 199fail: 200 /* EFI init failed, so hang. */ 201 hlt 202 jmp fail 2032: 204 movl BP_code32_start(%esi), %eax 205 leal startup_32(%eax), %eax 206 jmp *%eax 207ENDPROC(efi32_stub_entry) 208#endif 209 210 .text 211relocated: 212 213/* 214 * Clear BSS (stack is currently empty) 215 */ 216 xorl %eax, %eax 217 leal _bss(%ebx), %edi 218 leal _ebss(%ebx), %ecx 219 subl %edi, %ecx 220 shrl $2, %ecx 221 rep stosl 222 223/* 224 * Adjust our own GOT 225 */ 226 leal _got(%ebx), %edx 227 leal _egot(%ebx), %ecx 2281: 229 cmpl %ecx, %edx 230 jae 2f 231 addl %ebx, (%edx) 232 addl $4, %edx 233 jmp 1b 2342: 235 236/* 237 * Do the extraction, and jump to the new kernel.. 238 */ 239 /* push arguments for extract_kernel: */ 240 pushl $z_output_len /* decompressed length, end of relocs */ 241 242 movl BP_init_size(%esi), %eax 243 subl $_end, %eax 244 movl %ebx, %ebp 245 subl %eax, %ebp 246 pushl %ebp /* output address */ 247 248 pushl $z_input_len /* input_len */ 249 leal input_data(%ebx), %eax 250 pushl %eax /* input_data */ 251 leal boot_heap(%ebx), %eax 252 pushl %eax /* heap area */ 253 pushl %esi /* real mode pointer */ 254 call extract_kernel /* returns kernel location in %eax */ 255 addl $24, %esp 256 257/* 258 * Jump to the extracted kernel. 259 */ 260 xorl %ebx, %ebx 261 jmp *%eax 262 263#ifdef CONFIG_EFI_STUB 264 .data 265efi32_config: 266 .fill 5,8,0 267 .long efi_call_phys 268 .long 0 269 .byte 0 270#endif 271 272/* 273 * Stack and heap for uncompression 274 */ 275 .bss 276 .balign 4 277boot_heap: 278 .fill BOOT_HEAP_SIZE, 1, 0 279boot_stack: 280 .fill BOOT_STACK_SIZE, 1, 0 281boot_stack_end: 282