4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
8 * head.S contains the 32-bit startup code.
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]
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
22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
27 #include <linux/init.h>
28 #include <linux/linkage.h>
29 #include <asm/segment.h>
30 #include <asm/pgtable_types.h>
31 #include <asm/page_types.h>
34 #include <asm/processor-flags.h>
35 #include <asm/asm-offsets.h>
41 * 32bit entry is 0 and it is ABI so immutable!
42 * If we come here directly from a bootloader,
43 * kernel(text+data+bss+brk) ramdisk, zero_page, command line
44 * all need to be under the 4G limit.
48 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
49 * us to not reload segments
51 testb $(1<<6), BP_loadflags(%esi)
55 movl $(__BOOT_DS), %eax
62 * Calculate the delta between where we were compiled to run
63 * at and where we were actually loaded at. This can only be done
64 * with a short local call on x86. Nothing else will tell us what
65 * address we are running at. The reserved chunk of the real-mode
66 * data at 0x1e4 (defined as a scratch field) are used as the stack
67 * for this calculation. Only 4 bytes are needed.
69 leal (BP_scratch+4)(%esi), %esp
74 /* setup a stack and make sure cpu supports long mode. */
75 movl $boot_stack_end, %eax
84 * Compute the delta between where we were compiled to run at
85 * and where the code will actually run at.
87 * %ebp contains the address we are loaded at by the boot loader and %ebx
88 * contains the address where we should move the kernel image temporarily
89 * for safe in-place decompression.
92 #ifdef CONFIG_RELOCATABLE
94 movl BP_kernel_alignment(%esi), %eax
100 movl $LOAD_PHYSICAL_ADDR, %ebx
103 /* Target address to relocate to for decompression */
104 addl $z_extract_offset, %ebx
107 * Prepare for entering 64 bit mode
110 /* Load new GDT with the 64bit segments using 32bit descriptor */
112 movl %eax, gdt+2(%ebp)
115 /* Enable PAE mode */
116 movl $(X86_CR4_PAE), %eax
120 * Build early 4G boot pagetable
122 /* Initialize Page tables to 0 */
123 leal pgtable(%ebx), %edi
125 movl $((4096*6)/4), %ecx
129 leal pgtable + 0(%ebx), %edi
130 leal 0x1007 (%edi), %eax
134 leal pgtable + 0x1000(%ebx), %edi
135 leal 0x1007(%edi), %eax
137 1: movl %eax, 0x00(%edi)
138 addl $0x00001000, %eax
144 leal pgtable + 0x2000(%ebx), %edi
145 movl $0x00000183, %eax
147 1: movl %eax, 0(%edi)
148 addl $0x00200000, %eax
153 /* Enable the boot page tables */
154 leal pgtable(%ebx), %eax
157 /* Enable Long mode in EFER (Extended Feature Enable Register) */
160 btsl $_EFER_LME, %eax
163 /* After gdt is loaded */
170 * Setup for the jump to 64bit mode
172 * When the jump is performend we will be in long mode but
173 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
174 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use
175 * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
176 * We place all of the values on our mini stack so lret can
177 * used to perform that far jump.
180 leal startup_64(%ebp), %eax
183 /* Enter paged protected Mode, activating Long Mode */
184 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
187 /* Jump from 32bit compatibility mode into 64bit mode. */
195 * 64bit entry is 0x200 and it is ABI so immutable!
196 * We come here either from startup_32 or directly from a
198 * If we come here from a bootloader, kernel(text+data+bss+brk),
199 * ramdisk, zero_page, command line could be above 4G.
200 * We depend on an identity mapped page table being provided
201 * that maps our entire kernel(text+data+bss+brk), zero page
204 #ifdef CONFIG_EFI_STUB
206 * The entry point for the PE/COFF executable is efi_pe_entry, so
207 * only legacy boot loaders will execute this jmp.
216 call make_boot_params
220 leaq startup_32(%rip), %rax
221 movl %eax, BP_code32_start(%rdx)
225 ENTRY(efi_stub_entry)
231 /* EFI init failed, so hang. */
235 movl BP_code32_start(%esi), %eax
236 leaq preferred_addr(%rax), %rax
242 /* Setup data segments. */
251 * Compute the decompressed kernel start address. It is where
252 * we were loaded at aligned to a 2M boundary. %rbp contains the
253 * decompressed kernel start address.
255 * If it is a relocatable kernel then decompress and run the kernel
256 * from load address aligned to 2MB addr, otherwise decompress and
257 * run the kernel from LOAD_PHYSICAL_ADDR
259 * We cannot rely on the calculation done in 32-bit mode, since we
260 * may have been invoked via the 64-bit entry point.
263 /* Start with the delta to where the kernel will run at. */
264 #ifdef CONFIG_RELOCATABLE
265 leaq startup_32(%rip) /* - $startup_32 */, %rbp
266 movl BP_kernel_alignment(%rsi), %eax
272 movq $LOAD_PHYSICAL_ADDR, %rbp
275 /* Target address to relocate to for decompression */
276 leaq z_extract_offset(%rbp), %rbx
278 /* Set up the stack */
279 leaq boot_stack_end(%rbx), %rsp
286 * Copy the compressed kernel to the end of our buffer
287 * where decompression in place becomes safe.
290 leaq (_bss-8)(%rip), %rsi
291 leaq (_bss-8)(%rbx), %rdi
292 movq $_bss /* - $startup_32 */, %rcx
300 * Jump to the relocated address.
302 leaq relocated(%rbx), %rax
309 * Clear BSS (stack is currently empty)
312 leaq _bss(%rip), %rdi
313 leaq _ebss(%rip), %rcx
321 leaq _got(%rip), %rdx
322 leaq _egot(%rip), %rcx
332 * Do the decompression, and jump to the new kernel..
334 pushq %rsi /* Save the real mode argument */
335 movq %rsi, %rdi /* real mode address */
336 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
337 leaq input_data(%rip), %rdx /* input_data */
338 movl $z_input_len, %ecx /* input_len */
339 movq %rbp, %r8 /* output target address */
340 call decompress_kernel
344 * Jump to the decompressed kernel.
350 /* This isn't an x86-64 CPU so hang */
355 #include "../../kernel/verify_cpu.S"
362 .quad 0x0000000000000000 /* NULL descriptor */
363 .quad 0x00af9a000000ffff /* __KERNEL_CS */
364 .quad 0x00cf92000000ffff /* __KERNEL_DS */
365 .quad 0x0080890000000000 /* TS descriptor */
366 .quad 0x0000000000000000 /* TS continued */
370 * Stack and heap for uncompression
375 .fill BOOT_HEAP_SIZE, 1, 0
377 .fill BOOT_STACK_SIZE, 1, 0
381 * Space for page tables (not in .bss so not zeroed)
383 .section ".pgtable","a",@nobits