1 /* SPDX-License-Identifier: GPL-2.0 */
5 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
9 * head.S contains the 32-bit startup code.
11 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
12 * the page directory will exist. The startup code will be overwritten by
13 * the page directory. [According to comments etc elsewhere on a compressed
14 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
16 * Page 0 is deliberately kept safe, since System Management Mode code in
17 * laptops may need to access the BIOS data stored there. This is also
18 * useful for future device drivers that either access the BIOS via VM86
23 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
28 #include <linux/init.h>
29 #include <linux/linkage.h>
30 #include <asm/segment.h>
33 #include <asm/processor-flags.h>
34 #include <asm/asm-offsets.h>
35 #include <asm/bootparam.h>
38 * Locally defined symbols should be marked hidden:
49 * 32bit entry is 0 and it is ABI so immutable!
50 * If we come here directly from a bootloader,
51 * kernel(text+data+bss+brk) ramdisk, zero_page, command line
52 * all need to be under the 4G limit.
56 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
57 * us to not reload segments
59 testb $KEEP_SEGMENTS, BP_loadflags(%esi)
63 movl $(__BOOT_DS), %eax
70 * Calculate the delta between where we were compiled to run
71 * at and where we were actually loaded at. This can only be done
72 * with a short local call on x86. Nothing else will tell us what
73 * address we are running at. The reserved chunk of the real-mode
74 * data at 0x1e4 (defined as a scratch field) are used as the stack
75 * for this calculation. Only 4 bytes are needed.
77 leal (BP_scratch+4)(%esi), %esp
82 /* setup a stack and make sure cpu supports long mode. */
83 movl $boot_stack_end, %eax
92 * Compute the delta between where we were compiled to run at
93 * and where the code will actually run at.
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.
100 #ifdef CONFIG_RELOCATABLE
102 movl BP_kernel_alignment(%esi), %eax
107 cmpl $LOAD_PHYSICAL_ADDR, %ebx
110 movl $LOAD_PHYSICAL_ADDR, %ebx
113 /* Target address to relocate to for decompression */
114 movl BP_init_size(%esi), %eax
119 * Prepare for entering 64 bit mode
122 /* Load new GDT with the 64bit segments using 32bit descriptor */
123 addl %ebp, gdt+2(%ebp)
126 /* Enable PAE mode */
128 orl $X86_CR4_PAE, %eax
132 * Build early 4G boot pagetable
134 /* Initialize Page tables to 0 */
135 leal pgtable(%ebx), %edi
137 movl $(BOOT_INIT_PGT_SIZE/4), %ecx
141 leal pgtable + 0(%ebx), %edi
142 leal 0x1007 (%edi), %eax
146 leal pgtable + 0x1000(%ebx), %edi
147 leal 0x1007(%edi), %eax
149 1: movl %eax, 0x00(%edi)
150 addl $0x00001000, %eax
156 leal pgtable + 0x2000(%ebx), %edi
157 movl $0x00000183, %eax
159 1: movl %eax, 0(%edi)
160 addl $0x00200000, %eax
165 /* Enable the boot page tables */
166 leal pgtable(%ebx), %eax
169 /* Enable Long mode in EFER (Extended Feature Enable Register) */
172 btsl $_EFER_LME, %eax
175 /* After gdt is loaded */
178 movl $__BOOT_TSS, %eax
182 * Setup for the jump to 64bit mode
184 * When the jump is performend we will be in long mode but
185 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
186 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use
187 * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
188 * We place all of the values on our mini stack so lret can
189 * used to perform that far jump.
192 leal startup_64(%ebp), %eax
193 #ifdef CONFIG_EFI_MIXED
194 movl efi32_config(%ebp), %ebx
197 leal handover_entry(%ebp), %eax
202 /* Enter paged protected Mode, activating Long Mode */
203 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
206 /* Jump from 32bit compatibility mode into 64bit mode. */
210 #ifdef CONFIG_EFI_MIXED
212 ENTRY(efi32_stub_entry)
213 add $0x4, %esp /* Discard return address */
218 leal (BP_scratch+4)(%esi), %esp
223 movl %ecx, efi32_config(%ebp)
224 movl %edx, efi32_config+8(%ebp)
225 sgdtl efi32_boot_gdt(%ebp)
227 leal efi32_config(%ebp), %eax
228 movl %eax, efi_config(%ebp)
231 ENDPROC(efi32_stub_entry)
238 * 64bit entry is 0x200 and it is ABI so immutable!
239 * We come here either from startup_32 or directly from a
241 * If we come here from a bootloader, kernel(text+data+bss+brk),
242 * ramdisk, zero_page, command line could be above 4G.
243 * We depend on an identity mapped page table being provided
244 * that maps our entire kernel(text+data+bss+brk), zero page
248 /* Setup data segments. */
257 * Compute the decompressed kernel start address. It is where
258 * we were loaded at aligned to a 2M boundary. %rbp contains the
259 * decompressed kernel start address.
261 * If it is a relocatable kernel then decompress and run the kernel
262 * from load address aligned to 2MB addr, otherwise decompress and
263 * run the kernel from LOAD_PHYSICAL_ADDR
265 * We cannot rely on the calculation done in 32-bit mode, since we
266 * may have been invoked via the 64-bit entry point.
269 /* Start with the delta to where the kernel will run at. */
270 #ifdef CONFIG_RELOCATABLE
271 leaq startup_32(%rip) /* - $startup_32 */, %rbp
272 movl BP_kernel_alignment(%rsi), %eax
277 cmpq $LOAD_PHYSICAL_ADDR, %rbp
280 movq $LOAD_PHYSICAL_ADDR, %rbp
283 /* Target address to relocate to for decompression */
284 movl BP_init_size(%rsi), %ebx
288 /* Set up the stack */
289 leaq boot_stack_end(%rbx), %rsp
291 #ifdef CONFIG_X86_5LEVEL
292 /* Check if 5-level paging has already enabled */
294 testl $X86_CR4_LA57, %eax
298 * At this point we are in long mode with 4-level paging enabled,
299 * but we want to enable 5-level paging.
301 * The problem is that we cannot do it directly. Setting LA57 in
302 * long mode would trigger #GP. So we need to switch off long mode
305 * NOTE: This is not going to work if bootloader put us above 4G
308 * The first step is go into compatibility mode.
311 /* Clear additional page table */
312 leaq lvl5_pgtable(%rbx), %rdi
314 movq $(PAGE_SIZE/8), %rcx
318 * Setup current CR3 as the first and only entry in a new top level
322 leaq 0x7 (%rdi), %rax
323 movq %rax, lvl5_pgtable(%rbx)
325 /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
327 leaq compatible_mode(%rip), %rax
338 * Copy the compressed kernel to the end of our buffer
339 * where decompression in place becomes safe.
342 leaq (_bss-8)(%rip), %rsi
343 leaq (_bss-8)(%rbx), %rdi
344 movq $_bss /* - $startup_32 */, %rcx
352 * Jump to the relocated address.
354 leaq relocated(%rbx), %rax
357 #ifdef CONFIG_EFI_STUB
359 /* The entry point for the PE/COFF executable is efi_pe_entry. */
361 movq %rcx, efi64_config(%rip) /* Handle */
362 movq %rdx, efi64_config+8(%rip) /* EFI System table pointer */
364 leaq efi64_config(%rip), %rax
365 movq %rax, efi_config(%rip)
372 * Relocate efi_config->call().
374 addq %rbp, efi64_config+40(%rip)
377 call make_boot_params
381 leaq startup_32(%rip), %rax
382 movl %eax, BP_code32_start(%rsi)
383 jmp 2f /* Skip the relocation */
391 * Relocate efi_config->call().
393 movq efi_config(%rip), %rax
396 movq efi_config(%rip), %rdi
402 /* EFI init failed, so hang. */
406 movl BP_code32_start(%esi), %eax
407 leaq startup_64(%rax), %rax
409 ENDPROC(efi_pe_entry)
412 ENTRY(efi64_stub_entry)
413 movq %rdi, efi64_config(%rip) /* Handle */
414 movq %rsi, efi64_config+8(%rip) /* EFI System table pointer */
416 leaq efi64_config(%rip), %rax
417 movq %rax, efi_config(%rip)
421 ENDPROC(efi64_stub_entry)
428 * Clear BSS (stack is currently empty)
431 leaq _bss(%rip), %rdi
432 leaq _ebss(%rip), %rcx
440 leaq _got(%rip), %rdx
441 leaq _egot(%rip), %rcx
451 * Do the extraction, and jump to the new kernel..
453 pushq %rsi /* Save the real mode argument */
454 movq %rsi, %rdi /* real mode address */
455 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
456 leaq input_data(%rip), %rdx /* input_data */
457 movl $z_input_len, %ecx /* input_len */
458 movq %rbp, %r8 /* output target address */
459 movq $z_output_len, %r9 /* decompressed length, end of relocs */
460 call extract_kernel /* returns kernel location in %rax */
464 * Jump to the decompressed kernel.
469 #ifdef CONFIG_X86_5LEVEL
471 /* Setup data and stack segments */
472 movl $__KERNEL_DS, %eax
478 btrl $X86_CR0_PG_BIT, %eax
481 /* Point CR3 to 5-level paging */
482 leal lvl5_pgtable(%ebx), %eax
485 /* Enable PAE and LA57 mode */
487 orl $(X86_CR4_PAE | X86_CR4_LA57), %eax
490 /* Calculate address we are running at */
495 /* Prepare stack for far return to Long Mode */
497 leal lvl5(%edi), %eax
500 /* Enable paging back */
501 movl $(X86_CR0_PG | X86_CR0_PE), %eax
508 /* This isn't an x86-64 CPU so hang */
513 #include "../../kernel/verify_cpu.S"
520 .quad 0x00cf9a000000ffff /* __KERNEL32_CS */
521 .quad 0x00af9a000000ffff /* __KERNEL_CS */
522 .quad 0x00cf92000000ffff /* __KERNEL_DS */
523 .quad 0x0080890000000000 /* TS descriptor */
524 .quad 0x0000000000000000 /* TS continued */
527 #ifdef CONFIG_EFI_STUB
531 #ifdef CONFIG_EFI_MIXED
544 #endif /* CONFIG_EFI_STUB */
547 * Stack and heap for uncompression
552 .fill BOOT_HEAP_SIZE, 1, 0
554 .fill BOOT_STACK_SIZE, 1, 0
558 * Space for page tables (not in .bss so not zeroed)
560 .section ".pgtable","a",@nobits
563 .fill BOOT_PGT_SIZE, 1, 0
564 #ifdef CONFIG_X86_5LEVEL
566 .fill PAGE_SIZE, 1, 0