xref: /openbmc/qemu/tests/tcg/x86_64/system/boot.S (revision b55d7d34) 
1/*
2 * x86_64 boot and support code
3 *
4 * Copyright 2019 Linaro
5 *
6 * This work is licensed under the terms of the GNU GPL, version 3 or later.
7 * See the COPYING file in the top-level directory.
8 *
9 * Unlike the i386 version we instead use Xen's PVHVM booting header
10 * which should drop us automatically into 32 bit mode ready to go. I've
11 * nabbed bits of the Linux kernel setup to achieve this.
12 *
13 * SPDX-License-Identifier: GPL-3.0-or-later
14 */
15
16        .section .head
17
18#define ELFNOTE_START(name, type, flags)	\
19.pushsection .note.name, flags,@note	;	\
20  .balign 4				;	\
21  .long 2f - 1f		/* namesz */	;	\
22  .long 4484f - 3f	/* descsz */	;	\
23  .long type				;	\
241:.asciz #name				;	\
252:.balign 4				;	\
263:
27
28#define ELFNOTE_END				\
294484:.balign 4				;	\
30.popsection				;
31
32#define ELFNOTE(name, type, desc)		\
33	ELFNOTE_START(name, type, "")		\
34		desc			;	\
35	ELFNOTE_END
36
37#define XEN_ELFNOTE_ENTRY          1
38#define XEN_ELFNOTE_HYPERCALL_PAGE 2
39#define XEN_ELFNOTE_VIRT_BASE      3
40#define XEN_ELFNOTE_PADDR_OFFSET   4
41#define XEN_ELFNOTE_PHYS32_ENTRY  18
42
43#define __ASM_FORM(x)	x
44#define __ASM_FORM_RAW(x)     x
45#define __ASM_FORM_COMMA(x) x,
46#define __ASM_SEL(a,b)           __ASM_FORM(b)
47#define __ASM_SEL_RAW(a,b)      __ASM_FORM_RAW(b)
48#define _ASM_PTR	__ASM_SEL(.long, .quad)
49
50	ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE,      _ASM_PTR 0x100000)
51	ELFNOTE(Xen, XEN_ELFNOTE_ENTRY,          _ASM_PTR _start)
52	ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY,   _ASM_PTR _start)    /* entry == virtbase */
53	ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET,   _ASM_PTR 0)
54
55       /*
56	* Entry point for PVH guests.
57	*
58	* Xen ABI specifies the following register state when we come here:
59	*
60	* - `ebx`: contains the physical memory address where the loader has placed
61	*          the boot start info structure.
62	* - `cr0`: bit 0 (PE) must be set. All the other writeable bits are cleared.
63	* - `cr4`: all bits are cleared.
64	* - `cs `: must be a 32-bit read/execute code segment with a base of ‘0’
65	*          and a limit of ‘0xFFFFFFFF’. The selector value is unspecified.
66	* - `ds`, `es`: must be a 32-bit read/write data segment with a base of
67	*               ‘0’ and a limit of ‘0xFFFFFFFF’. The selector values are all
68	*               unspecified.
69	* - `tr`: must be a 32-bit TSS (active) with a base of '0' and a limit
70	*         of '0x67'.
71	* - `eflags`: bit 17 (VM) must be cleared. Bit 9 (IF) must be cleared.
72	*             Bit 8 (TF) must be cleared. Other bits are all unspecified.
73	*
74	* All other processor registers and flag bits are unspecified. The OS is in
75	* charge of setting up it's own stack, GDT and IDT.
76	*/
77        .code32
78        .section .text
79
80.global _start
81_start:
82	cld
83        lgdt gdtr
84
85        ljmp $0x8,$.Lloadcs
86.Lloadcs:
87        mov $0x10,%eax
88        mov %eax,%ds
89        mov %eax,%es
90        mov %eax,%fs
91        mov %eax,%gs
92        mov %eax,%ss
93
94	/* Enable PAE mode (bit 5). */
95	mov %cr4, %eax
96	btsl $5, %eax
97	mov %eax, %cr4
98
99#define MSR_EFER		0xc0000080 /* extended feature register */
100
101	/* Enable Long mode. */
102	mov $MSR_EFER, %ecx
103	rdmsr
104	btsl $8, %eax
105	wrmsr
106
107	/* Enable paging */
108	mov $.Lpml4, %ecx
109	mov %ecx, %cr3
110
111	mov %cr0, %eax
112	btsl $31, %eax
113	mov %eax, %cr0
114
115	/* Jump to 64-bit mode. */
116        lgdt gdtr64
117        ljmp $0x8,$.Lenter64
118
119        .code64
120        .section .text
121.Lenter64:
122
123
124	// Setup stack ASAP
125	movq $stack_end,%rsp
126
127        /* don't worry about stack frame, assume everthing is garbage when we return */
128	call main
129
130        /* output any non-zero result in eax to isa-debug-exit device */
131        test %al, %al
132        jz 1f
133        out %ax, $0xf4
134
1351:      /* QEMU ACPI poweroff */
136	mov $0x604,%edx
137	mov $0x2000,%eax
138	out %ax,%dx
139	hlt
140	jmp 1b
141
142        /*
143         * Helper Functions
144         *
145         * x86_64 calling convention is rdi, rsi, rdx, rcx, r8, r9
146         */
147
148        /* Output a single character to serial port */
149        .global __sys_outc
150__sys_outc:
151        pushq %rax
152        mov %rax, %rdx
153	out %al,$0xE9
154        popq %rax
155        ret
156
157	/* Interrupt Descriptor Table */
158
159        .section .data
160        .align 16
161
162idt_00: .int 0, 0
163idt_01: .int 0, 0
164idt_02: .int 0, 0
165idt_03: .int 0, 0
166idt_04: .int 0, 0
167idt_05: .int 0, 0
168idt_06: .int 0, 0 /* intr_6_opcode, Invalid Opcode */
169idt_07: .int 0, 0
170idt_08: .int 0, 0
171idt_09: .int 0, 0
172idt_0A: .int 0, 0
173idt_0B: .int 0, 0
174idt_0C: .int 0, 0
175idt_0D: .int 0, 0
176idt_0E: .int 0, 0
177idt_0F: .int 0, 0
178idt_10: .int 0, 0
179idt_11: .int 0, 0
180idt_12: .int 0, 0
181idt_13: .int 0, 0
182idt_14: .int 0, 0
183idt_15: .int 0, 0
184idt_16: .int 0, 0
185idt_17: .int 0, 0
186idt_18: .int 0, 0
187idt_19: .int 0, 0
188idt_1A: .int 0, 0
189idt_1B: .int 0, 0
190idt_1C: .int 0, 0
191idt_1D: .int 0, 0
192idt_1E: .int 0, 0
193idt_1F: .int 0, 0
194
195
196	/*
197	 * Global Descriptor Table (GDT)
198	 *
199	 * This describes various memory areas (segments) through
200	 * segment descriptors. In 32 bit mode each segment each
201	 * segement is associated with segment registers which are
202	 * implicitly (or explicitly) referenced depending on the
203	 * instruction. However in 64 bit mode selectors are flat and
204	 * segmented addressing isn't used.
205	 */
206gdt:
207        .short 0
208gdtr:
209        .short gdt_en - gdt - 1
210        .int gdt
211
212        // Code cs:
213        .short 0xFFFF
214        .short 0
215        .byte 0
216        .byte 0x9b
217        .byte 0xCF
218        .byte 0
219
220        // Data  ds:, ss:, es:, fs:, and gs:
221        .short 0xFFFF
222        .short 0
223        .byte 0
224        .byte 0x93
225        .byte 0xCF
226        .byte 0
227gdt_en:
228
229gdt64:
230        .short 0
231gdtr64:
232        .short gdt64_en - gdt64 - 1
233        .int gdt64
234
235        // Code
236        .short 0xFFFF
237        .short 0
238        .byte 0
239        .byte 0x9b
240        .byte 0xAF
241        .byte 0
242
243        // Data
244        .short 0xFFFF
245        .short 0
246        .byte 0
247        .byte 0x93
248        .byte 0xCF
249        .byte 0
250gdt64_en:
251
252	.section .bss
253        .align 16
254
255stack: .space 65536
256stack_end:
257
258	.section .data
259
260.align 4096
261.Lpd:
262i = 0
263        .rept 512 * 4
264        .quad 0x1e7 | (i << 21)
265        i = i + 1
266        .endr
267
268.align 4096
269.Lpdp:
270        .quad .Lpd + 7 + 0 * 4096 /* 0-1 GB */
271        .quad .Lpd + 7 + 1 * 4096 /* 1-2 GB */
272        .quad .Lpd + 7 + 2 * 4096 /* 2-3 GB */
273        .quad .Lpd + 7 + 3 * 4096 /* 3-4 GB */
274
275.align 4096
276.Lpml4:
277        .quad .Lpdp + 7 /* 0-512 GB */
278