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/linkage.h>
28 #include <asm/segment.h>
29 #include <asm/pgtable_types.h>
30 #include <asm/page_types.h>
33 #include <asm/processor-flags.h>
34 #include <asm/asm-offsets.h>
41 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
42 * us to not reload segments
44 testb $(1<<6), BP_loadflags(%esi)
48 movl $(__KERNEL_DS), %eax
55 * Calculate the delta between where we were compiled to run
56 * at and where we were actually loaded at. This can only be done
57 * with a short local call on x86. Nothing else will tell us what
58 * address we are running at. The reserved chunk of the real-mode
59 * data at 0x1e4 (defined as a scratch field) are used as the stack
60 * for this calculation. Only 4 bytes are needed.
62 leal (BP_scratch+4)(%esi), %esp
67 /* setup a stack and make sure cpu supports long mode. */
68 movl $boot_stack_end, %eax
77 * Compute the delta between where we were compiled to run at
78 * and where the code will actually run at.
80 * %ebp contains the address we are loaded at by the boot loader and %ebx
81 * contains the address where we should move the kernel image temporarily
82 * for safe in-place decompression.
85 #ifdef CONFIG_RELOCATABLE
87 addl $(PMD_PAGE_SIZE -1), %ebx
88 andl $PMD_PAGE_MASK, %ebx
90 movl $CONFIG_PHYSICAL_START, %ebx
93 /* Replace the compressed data size with the uncompressed size */
94 subl input_len(%ebp), %ebx
95 movl output_len(%ebp), %eax
97 /* Add 8 bytes for every 32K input block */
100 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */
101 addl $(32768 + 18 + 4095), %ebx
105 * Prepare for entering 64 bit mode
108 /* Load new GDT with the 64bit segments using 32bit descriptor */
110 movl %eax, gdt+2(%ebp)
113 /* Enable PAE mode */
115 orl $(X86_CR4_PAE), %eax
119 * Build early 4G boot pagetable
121 /* Initialize Page tables to 0 */
122 leal pgtable(%ebx), %edi
124 movl $((4096*6)/4), %ecx
128 leal pgtable + 0(%ebx), %edi
129 leal 0x1007 (%edi), %eax
133 leal pgtable + 0x1000(%ebx), %edi
134 leal 0x1007(%edi), %eax
136 1: movl %eax, 0x00(%edi)
137 addl $0x00001000, %eax
143 leal pgtable + 0x2000(%ebx), %edi
144 movl $0x00000183, %eax
146 1: movl %eax, 0(%edi)
147 addl $0x00200000, %eax
152 /* Enable the boot page tables */
153 leal pgtable(%ebx), %eax
156 /* Enable Long mode in EFER (Extended Feature Enable Register) */
159 btsl $_EFER_LME, %eax
163 * Setup for the jump to 64bit mode
165 * When the jump is performend we will be in long mode but
166 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
167 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use
168 * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
169 * We place all of the values on our mini stack so lret can
170 * used to perform that far jump.
173 leal startup_64(%ebp), %eax
176 /* Enter paged protected Mode, activating Long Mode */
177 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
180 /* Jump from 32bit compatibility mode into 64bit mode. */
185 /* This isn't an x86-64 CPU so hang */
190 #include "../../kernel/verify_cpu_64.S"
193 * Be careful here startup_64 needs to be at a predictable
194 * address so I can export it in an ELF header. Bootloaders
195 * should look at the ELF header to find this address, as
196 * it may change in the future.
202 * We come here either from startup_32 or directly from a
203 * 64bit bootloader. If we come here from a bootloader we depend on
204 * an identity mapped page table being provied that maps our
205 * entire text+data+bss and hopefully all of memory.
208 /* Setup data segments. */
220 * Compute the decompressed kernel start address. It is where
221 * we were loaded at aligned to a 2M boundary. %rbp contains the
222 * decompressed kernel start address.
224 * If it is a relocatable kernel then decompress and run the kernel
225 * from load address aligned to 2MB addr, otherwise decompress and
226 * run the kernel from CONFIG_PHYSICAL_START
229 /* Start with the delta to where the kernel will run at. */
230 #ifdef CONFIG_RELOCATABLE
231 leaq startup_32(%rip) /* - $startup_32 */, %rbp
232 addq $(PMD_PAGE_SIZE - 1), %rbp
233 andq $PMD_PAGE_MASK, %rbp
236 movq $CONFIG_PHYSICAL_START, %rbp
240 /* Replace the compressed data size with the uncompressed size */
241 movl input_len(%rip), %eax
243 movl output_len(%rip), %eax
245 /* Add 8 bytes for every 32K input block */
248 /* Add 32K + 18 bytes of extra slack and align on a 4K boundary */
249 addq $(32768 + 18 + 4095), %rbx
253 * Copy the compressed kernel to the end of our buffer
254 * where decompression in place becomes safe.
256 leaq _end_before_pgt(%rip), %r8
257 leaq _end_before_pgt(%rbx), %r9
258 movq $_end_before_pgt /* - $startup_32 */, %rcx
267 * Jump to the relocated address.
269 leaq relocated(%rbx), %rax
279 leaq _edata(%rbx), %rdi
280 leaq _end_before_pgt(%rbx), %rcx
285 /* Setup the stack */
286 leaq boot_stack_end(%rip), %rsp
288 /* zero EFLAGS after setting rsp */
293 * Do the decompression, and jump to the new kernel..
295 pushq %rsi # Save the real mode argument
296 movq %rsi, %rdi # real mode address
297 leaq boot_heap(%rip), %rsi # malloc area for uncompression
298 leaq input_data(%rip), %rdx # input_data
299 movl input_len(%rip), %eax
300 movq %rax, %rcx # input_len
301 movq %rbp, %r8 # output
302 call decompress_kernel
306 * Jump to the decompressed kernel.
315 .quad 0x0000000000000000 /* NULL descriptor */
316 .quad 0x00af9a000000ffff /* __KERNEL_CS */
317 .quad 0x00cf92000000ffff /* __KERNEL_DS */
318 .quad 0x0080890000000000 /* TS descriptor */
319 .quad 0x0000000000000000 /* TS continued */
323 * Stack and heap for uncompression
328 .fill BOOT_HEAP_SIZE, 1, 0
330 .fill BOOT_STACK_SIZE, 1, 0