xref: /openbmc/qemu/hw/arm/boot.c (revision 3ae59580)
1 /*
2  * ARM kernel loader.
3  *
4  * Copyright (c) 2006-2007 CodeSourcery.
5  * Written by Paul Brook
6  *
7  * This code is licensed under the GPL.
8  */
9 
10 #include "config.h"
11 #include "hw/hw.h"
12 #include "hw/arm/arm.h"
13 #include "sysemu/sysemu.h"
14 #include "hw/boards.h"
15 #include "hw/loader.h"
16 #include "elf.h"
17 #include "sysemu/device_tree.h"
18 #include "qemu/config-file.h"
19 #include "exec/address-spaces.h"
20 
21 /* Kernel boot protocol is specified in the kernel docs
22  * Documentation/arm/Booting and Documentation/arm64/booting.txt
23  * They have different preferred image load offsets from system RAM base.
24  */
25 #define KERNEL_ARGS_ADDR 0x100
26 #define KERNEL_LOAD_ADDR 0x00010000
27 #define KERNEL64_LOAD_ADDR 0x00080000
28 
29 typedef enum {
30     FIXUP_NONE = 0,   /* do nothing */
31     FIXUP_TERMINATOR, /* end of insns */
32     FIXUP_BOARDID,    /* overwrite with board ID number */
33     FIXUP_ARGPTR,     /* overwrite with pointer to kernel args */
34     FIXUP_ENTRYPOINT, /* overwrite with kernel entry point */
35     FIXUP_GIC_CPU_IF, /* overwrite with GIC CPU interface address */
36     FIXUP_BOOTREG,    /* overwrite with boot register address */
37     FIXUP_DSB,        /* overwrite with correct DSB insn for cpu */
38     FIXUP_MAX,
39 } FixupType;
40 
41 typedef struct ARMInsnFixup {
42     uint32_t insn;
43     FixupType fixup;
44 } ARMInsnFixup;
45 
46 static const ARMInsnFixup bootloader_aarch64[] = {
47     { 0x580000c0 }, /* ldr x0, arg ; Load the lower 32-bits of DTB */
48     { 0xaa1f03e1 }, /* mov x1, xzr */
49     { 0xaa1f03e2 }, /* mov x2, xzr */
50     { 0xaa1f03e3 }, /* mov x3, xzr */
51     { 0x58000084 }, /* ldr x4, entry ; Load the lower 32-bits of kernel entry */
52     { 0xd61f0080 }, /* br x4      ; Jump to the kernel entry point */
53     { 0, FIXUP_ARGPTR }, /* arg: .word @DTB Lower 32-bits */
54     { 0 }, /* .word @DTB Higher 32-bits */
55     { 0, FIXUP_ENTRYPOINT }, /* entry: .word @Kernel Entry Lower 32-bits */
56     { 0 }, /* .word @Kernel Entry Higher 32-bits */
57     { 0, FIXUP_TERMINATOR }
58 };
59 
60 /* The worlds second smallest bootloader.  Set r0-r2, then jump to kernel.  */
61 static const ARMInsnFixup bootloader[] = {
62     { 0xe3a00000 }, /* mov     r0, #0 */
63     { 0xe59f1004 }, /* ldr     r1, [pc, #4] */
64     { 0xe59f2004 }, /* ldr     r2, [pc, #4] */
65     { 0xe59ff004 }, /* ldr     pc, [pc, #4] */
66     { 0, FIXUP_BOARDID },
67     { 0, FIXUP_ARGPTR },
68     { 0, FIXUP_ENTRYPOINT },
69     { 0, FIXUP_TERMINATOR }
70 };
71 
72 /* Handling for secondary CPU boot in a multicore system.
73  * Unlike the uniprocessor/primary CPU boot, this is platform
74  * dependent. The default code here is based on the secondary
75  * CPU boot protocol used on realview/vexpress boards, with
76  * some parameterisation to increase its flexibility.
77  * QEMU platform models for which this code is not appropriate
78  * should override write_secondary_boot and secondary_cpu_reset_hook
79  * instead.
80  *
81  * This code enables the interrupt controllers for the secondary
82  * CPUs and then puts all the secondary CPUs into a loop waiting
83  * for an interprocessor interrupt and polling a configurable
84  * location for the kernel secondary CPU entry point.
85  */
86 #define DSB_INSN 0xf57ff04f
87 #define CP15_DSB_INSN 0xee070f9a /* mcr cp15, 0, r0, c7, c10, 4 */
88 
89 static const ARMInsnFixup smpboot[] = {
90     { 0xe59f2028 }, /* ldr r2, gic_cpu_if */
91     { 0xe59f0028 }, /* ldr r0, bootreg_addr */
92     { 0xe3a01001 }, /* mov r1, #1 */
93     { 0xe5821000 }, /* str r1, [r2] - set GICC_CTLR.Enable */
94     { 0xe3a010ff }, /* mov r1, #0xff */
95     { 0xe5821004 }, /* str r1, [r2, 4] - set GIC_PMR.Priority to 0xff */
96     { 0, FIXUP_DSB },   /* dsb */
97     { 0xe320f003 }, /* wfi */
98     { 0xe5901000 }, /* ldr     r1, [r0] */
99     { 0xe1110001 }, /* tst     r1, r1 */
100     { 0x0afffffb }, /* beq     <wfi> */
101     { 0xe12fff11 }, /* bx      r1 */
102     { 0, FIXUP_GIC_CPU_IF }, /* gic_cpu_if: .word 0x.... */
103     { 0, FIXUP_BOOTREG }, /* bootreg_addr: .word 0x.... */
104     { 0, FIXUP_TERMINATOR }
105 };
106 
107 static void write_bootloader(const char *name, hwaddr addr,
108                              const ARMInsnFixup *insns, uint32_t *fixupcontext)
109 {
110     /* Fix up the specified bootloader fragment and write it into
111      * guest memory using rom_add_blob_fixed(). fixupcontext is
112      * an array giving the values to write in for the fixup types
113      * which write a value into the code array.
114      */
115     int i, len;
116     uint32_t *code;
117 
118     len = 0;
119     while (insns[len].fixup != FIXUP_TERMINATOR) {
120         len++;
121     }
122 
123     code = g_new0(uint32_t, len);
124 
125     for (i = 0; i < len; i++) {
126         uint32_t insn = insns[i].insn;
127         FixupType fixup = insns[i].fixup;
128 
129         switch (fixup) {
130         case FIXUP_NONE:
131             break;
132         case FIXUP_BOARDID:
133         case FIXUP_ARGPTR:
134         case FIXUP_ENTRYPOINT:
135         case FIXUP_GIC_CPU_IF:
136         case FIXUP_BOOTREG:
137         case FIXUP_DSB:
138             insn = fixupcontext[fixup];
139             break;
140         default:
141             abort();
142         }
143         code[i] = tswap32(insn);
144     }
145 
146     rom_add_blob_fixed(name, code, len * sizeof(uint32_t), addr);
147 
148     g_free(code);
149 }
150 
151 static void default_write_secondary(ARMCPU *cpu,
152                                     const struct arm_boot_info *info)
153 {
154     uint32_t fixupcontext[FIXUP_MAX];
155 
156     fixupcontext[FIXUP_GIC_CPU_IF] = info->gic_cpu_if_addr;
157     fixupcontext[FIXUP_BOOTREG] = info->smp_bootreg_addr;
158     if (arm_feature(&cpu->env, ARM_FEATURE_V7)) {
159         fixupcontext[FIXUP_DSB] = DSB_INSN;
160     } else {
161         fixupcontext[FIXUP_DSB] = CP15_DSB_INSN;
162     }
163 
164     write_bootloader("smpboot", info->smp_loader_start,
165                      smpboot, fixupcontext);
166 }
167 
168 static void default_reset_secondary(ARMCPU *cpu,
169                                     const struct arm_boot_info *info)
170 {
171     CPUARMState *env = &cpu->env;
172 
173     stl_phys_notdirty(&address_space_memory, info->smp_bootreg_addr, 0);
174     env->regs[15] = info->smp_loader_start;
175 }
176 
177 static inline bool have_dtb(const struct arm_boot_info *info)
178 {
179     return info->dtb_filename || info->get_dtb;
180 }
181 
182 #define WRITE_WORD(p, value) do { \
183     stl_phys_notdirty(&address_space_memory, p, value);  \
184     p += 4;                       \
185 } while (0)
186 
187 static void set_kernel_args(const struct arm_boot_info *info)
188 {
189     int initrd_size = info->initrd_size;
190     hwaddr base = info->loader_start;
191     hwaddr p;
192 
193     p = base + KERNEL_ARGS_ADDR;
194     /* ATAG_CORE */
195     WRITE_WORD(p, 5);
196     WRITE_WORD(p, 0x54410001);
197     WRITE_WORD(p, 1);
198     WRITE_WORD(p, 0x1000);
199     WRITE_WORD(p, 0);
200     /* ATAG_MEM */
201     /* TODO: handle multiple chips on one ATAG list */
202     WRITE_WORD(p, 4);
203     WRITE_WORD(p, 0x54410002);
204     WRITE_WORD(p, info->ram_size);
205     WRITE_WORD(p, info->loader_start);
206     if (initrd_size) {
207         /* ATAG_INITRD2 */
208         WRITE_WORD(p, 4);
209         WRITE_WORD(p, 0x54420005);
210         WRITE_WORD(p, info->initrd_start);
211         WRITE_WORD(p, initrd_size);
212     }
213     if (info->kernel_cmdline && *info->kernel_cmdline) {
214         /* ATAG_CMDLINE */
215         int cmdline_size;
216 
217         cmdline_size = strlen(info->kernel_cmdline);
218         cpu_physical_memory_write(p + 8, info->kernel_cmdline,
219                                   cmdline_size + 1);
220         cmdline_size = (cmdline_size >> 2) + 1;
221         WRITE_WORD(p, cmdline_size + 2);
222         WRITE_WORD(p, 0x54410009);
223         p += cmdline_size * 4;
224     }
225     if (info->atag_board) {
226         /* ATAG_BOARD */
227         int atag_board_len;
228         uint8_t atag_board_buf[0x1000];
229 
230         atag_board_len = (info->atag_board(info, atag_board_buf) + 3) & ~3;
231         WRITE_WORD(p, (atag_board_len + 8) >> 2);
232         WRITE_WORD(p, 0x414f4d50);
233         cpu_physical_memory_write(p, atag_board_buf, atag_board_len);
234         p += atag_board_len;
235     }
236     /* ATAG_END */
237     WRITE_WORD(p, 0);
238     WRITE_WORD(p, 0);
239 }
240 
241 static void set_kernel_args_old(const struct arm_boot_info *info)
242 {
243     hwaddr p;
244     const char *s;
245     int initrd_size = info->initrd_size;
246     hwaddr base = info->loader_start;
247 
248     /* see linux/include/asm-arm/setup.h */
249     p = base + KERNEL_ARGS_ADDR;
250     /* page_size */
251     WRITE_WORD(p, 4096);
252     /* nr_pages */
253     WRITE_WORD(p, info->ram_size / 4096);
254     /* ramdisk_size */
255     WRITE_WORD(p, 0);
256 #define FLAG_READONLY	1
257 #define FLAG_RDLOAD	4
258 #define FLAG_RDPROMPT	8
259     /* flags */
260     WRITE_WORD(p, FLAG_READONLY | FLAG_RDLOAD | FLAG_RDPROMPT);
261     /* rootdev */
262     WRITE_WORD(p, (31 << 8) | 0);	/* /dev/mtdblock0 */
263     /* video_num_cols */
264     WRITE_WORD(p, 0);
265     /* video_num_rows */
266     WRITE_WORD(p, 0);
267     /* video_x */
268     WRITE_WORD(p, 0);
269     /* video_y */
270     WRITE_WORD(p, 0);
271     /* memc_control_reg */
272     WRITE_WORD(p, 0);
273     /* unsigned char sounddefault */
274     /* unsigned char adfsdrives */
275     /* unsigned char bytes_per_char_h */
276     /* unsigned char bytes_per_char_v */
277     WRITE_WORD(p, 0);
278     /* pages_in_bank[4] */
279     WRITE_WORD(p, 0);
280     WRITE_WORD(p, 0);
281     WRITE_WORD(p, 0);
282     WRITE_WORD(p, 0);
283     /* pages_in_vram */
284     WRITE_WORD(p, 0);
285     /* initrd_start */
286     if (initrd_size) {
287         WRITE_WORD(p, info->initrd_start);
288     } else {
289         WRITE_WORD(p, 0);
290     }
291     /* initrd_size */
292     WRITE_WORD(p, initrd_size);
293     /* rd_start */
294     WRITE_WORD(p, 0);
295     /* system_rev */
296     WRITE_WORD(p, 0);
297     /* system_serial_low */
298     WRITE_WORD(p, 0);
299     /* system_serial_high */
300     WRITE_WORD(p, 0);
301     /* mem_fclk_21285 */
302     WRITE_WORD(p, 0);
303     /* zero unused fields */
304     while (p < base + KERNEL_ARGS_ADDR + 256 + 1024) {
305         WRITE_WORD(p, 0);
306     }
307     s = info->kernel_cmdline;
308     if (s) {
309         cpu_physical_memory_write(p, s, strlen(s) + 1);
310     } else {
311         WRITE_WORD(p, 0);
312     }
313 }
314 
315 /**
316  * load_dtb() - load a device tree binary image into memory
317  * @addr:       the address to load the image at
318  * @binfo:      struct describing the boot environment
319  * @addr_limit: upper limit of the available memory area at @addr
320  *
321  * Load a device tree supplied by the machine or by the user  with the
322  * '-dtb' command line option, and put it at offset @addr in target
323  * memory.
324  *
325  * If @addr_limit contains a meaningful value (i.e., it is strictly greater
326  * than @addr), the device tree is only loaded if its size does not exceed
327  * the limit.
328  *
329  * Returns: the size of the device tree image on success,
330  *          0 if the image size exceeds the limit,
331  *          -1 on errors.
332  */
333 static int load_dtb(hwaddr addr, const struct arm_boot_info *binfo,
334                     hwaddr addr_limit)
335 {
336     void *fdt = NULL;
337     int size, rc;
338     uint32_t acells, scells;
339 
340     if (binfo->dtb_filename) {
341         char *filename;
342         filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, binfo->dtb_filename);
343         if (!filename) {
344             fprintf(stderr, "Couldn't open dtb file %s\n", binfo->dtb_filename);
345             goto fail;
346         }
347 
348         fdt = load_device_tree(filename, &size);
349         if (!fdt) {
350             fprintf(stderr, "Couldn't open dtb file %s\n", filename);
351             g_free(filename);
352             goto fail;
353         }
354         g_free(filename);
355     } else if (binfo->get_dtb) {
356         fdt = binfo->get_dtb(binfo, &size);
357         if (!fdt) {
358             fprintf(stderr, "Board was unable to create a dtb blob\n");
359             goto fail;
360         }
361     }
362 
363     if (addr_limit > addr && size > (addr_limit - addr)) {
364         /* Installing the device tree blob at addr would exceed addr_limit.
365          * Whether this constitutes failure is up to the caller to decide,
366          * so just return 0 as size, i.e., no error.
367          */
368         g_free(fdt);
369         return 0;
370     }
371 
372     acells = qemu_fdt_getprop_cell(fdt, "/", "#address-cells");
373     scells = qemu_fdt_getprop_cell(fdt, "/", "#size-cells");
374     if (acells == 0 || scells == 0) {
375         fprintf(stderr, "dtb file invalid (#address-cells or #size-cells 0)\n");
376         goto fail;
377     }
378 
379     if (scells < 2 && binfo->ram_size >= (1ULL << 32)) {
380         /* This is user error so deserves a friendlier error message
381          * than the failure of setprop_sized_cells would provide
382          */
383         fprintf(stderr, "qemu: dtb file not compatible with "
384                 "RAM size > 4GB\n");
385         goto fail;
386     }
387 
388     rc = qemu_fdt_setprop_sized_cells(fdt, "/memory", "reg",
389                                       acells, binfo->loader_start,
390                                       scells, binfo->ram_size);
391     if (rc < 0) {
392         fprintf(stderr, "couldn't set /memory/reg\n");
393         goto fail;
394     }
395 
396     if (binfo->kernel_cmdline && *binfo->kernel_cmdline) {
397         rc = qemu_fdt_setprop_string(fdt, "/chosen", "bootargs",
398                                      binfo->kernel_cmdline);
399         if (rc < 0) {
400             fprintf(stderr, "couldn't set /chosen/bootargs\n");
401             goto fail;
402         }
403     }
404 
405     if (binfo->initrd_size) {
406         rc = qemu_fdt_setprop_cell(fdt, "/chosen", "linux,initrd-start",
407                                    binfo->initrd_start);
408         if (rc < 0) {
409             fprintf(stderr, "couldn't set /chosen/linux,initrd-start\n");
410             goto fail;
411         }
412 
413         rc = qemu_fdt_setprop_cell(fdt, "/chosen", "linux,initrd-end",
414                                    binfo->initrd_start + binfo->initrd_size);
415         if (rc < 0) {
416             fprintf(stderr, "couldn't set /chosen/linux,initrd-end\n");
417             goto fail;
418         }
419     }
420 
421     if (binfo->modify_dtb) {
422         binfo->modify_dtb(binfo, fdt);
423     }
424 
425     qemu_fdt_dumpdtb(fdt, size);
426 
427     /* Put the DTB into the memory map as a ROM image: this will ensure
428      * the DTB is copied again upon reset, even if addr points into RAM.
429      */
430     rom_add_blob_fixed("dtb", fdt, size, addr);
431 
432     g_free(fdt);
433 
434     return size;
435 
436 fail:
437     g_free(fdt);
438     return -1;
439 }
440 
441 static void do_cpu_reset(void *opaque)
442 {
443     ARMCPU *cpu = opaque;
444     CPUARMState *env = &cpu->env;
445     const struct arm_boot_info *info = env->boot_info;
446 
447     cpu_reset(CPU(cpu));
448     if (info) {
449         if (!info->is_linux) {
450             /* Jump to the entry point.  */
451             if (env->aarch64) {
452                 env->pc = info->entry;
453             } else {
454                 env->regs[15] = info->entry & 0xfffffffe;
455                 env->thumb = info->entry & 1;
456             }
457         } else {
458             if (CPU(cpu) == first_cpu) {
459                 if (env->aarch64) {
460                     env->pc = info->loader_start;
461                 } else {
462                     env->regs[15] = info->loader_start;
463                 }
464 
465                 if (!have_dtb(info)) {
466                     if (old_param) {
467                         set_kernel_args_old(info);
468                     } else {
469                         set_kernel_args(info);
470                     }
471                 }
472             } else {
473                 info->secondary_cpu_reset_hook(cpu, info);
474             }
475         }
476     }
477 }
478 
479 void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
480 {
481     CPUState *cs = CPU(cpu);
482     int kernel_size;
483     int initrd_size;
484     int is_linux = 0;
485     uint64_t elf_entry, elf_low_addr, elf_high_addr;
486     int elf_machine;
487     hwaddr entry, kernel_load_offset;
488     int big_endian;
489     static const ARMInsnFixup *primary_loader;
490 
491     /* Load the kernel.  */
492     if (!info->kernel_filename) {
493 
494         if (have_dtb(info)) {
495             /* If we have a device tree blob, but no kernel to supply it to,
496              * copy it to the base of RAM for a bootloader to pick up.
497              */
498             if (load_dtb(info->loader_start, info, 0) < 0) {
499                 exit(1);
500             }
501         }
502 
503         /* If no kernel specified, do nothing; we will start from address 0
504          * (typically a boot ROM image) in the same way as hardware.
505          */
506         return;
507     }
508 
509     if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
510         primary_loader = bootloader_aarch64;
511         kernel_load_offset = KERNEL64_LOAD_ADDR;
512         elf_machine = EM_AARCH64;
513     } else {
514         primary_loader = bootloader;
515         kernel_load_offset = KERNEL_LOAD_ADDR;
516         elf_machine = EM_ARM;
517     }
518 
519     info->dtb_filename = qemu_opt_get(qemu_get_machine_opts(), "dtb");
520 
521     if (!info->secondary_cpu_reset_hook) {
522         info->secondary_cpu_reset_hook = default_reset_secondary;
523     }
524     if (!info->write_secondary_boot) {
525         info->write_secondary_boot = default_write_secondary;
526     }
527 
528     if (info->nb_cpus == 0)
529         info->nb_cpus = 1;
530 
531 #ifdef TARGET_WORDS_BIGENDIAN
532     big_endian = 1;
533 #else
534     big_endian = 0;
535 #endif
536 
537     /* We want to put the initrd far enough into RAM that when the
538      * kernel is uncompressed it will not clobber the initrd. However
539      * on boards without much RAM we must ensure that we still leave
540      * enough room for a decent sized initrd, and on boards with large
541      * amounts of RAM we must avoid the initrd being so far up in RAM
542      * that it is outside lowmem and inaccessible to the kernel.
543      * So for boards with less  than 256MB of RAM we put the initrd
544      * halfway into RAM, and for boards with 256MB of RAM or more we put
545      * the initrd at 128MB.
546      */
547     info->initrd_start = info->loader_start +
548         MIN(info->ram_size / 2, 128 * 1024 * 1024);
549 
550     /* Assume that raw images are linux kernels, and ELF images are not.  */
551     kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
552                            &elf_low_addr, &elf_high_addr, big_endian,
553                            elf_machine, 1);
554     if (kernel_size > 0 && have_dtb(info)) {
555         /* If there is still some room left at the base of RAM, try and put
556          * the DTB there like we do for images loaded with -bios or -pflash.
557          */
558         if (elf_low_addr > info->loader_start
559             || elf_high_addr < info->loader_start) {
560             /* Pass elf_low_addr as address limit to load_dtb if it may be
561              * pointing into RAM, otherwise pass '0' (no limit)
562              */
563             if (elf_low_addr < info->loader_start) {
564                 elf_low_addr = 0;
565             }
566             if (load_dtb(info->loader_start, info, elf_low_addr) < 0) {
567                 exit(1);
568             }
569         }
570     }
571     entry = elf_entry;
572     if (kernel_size < 0) {
573         kernel_size = load_uimage(info->kernel_filename, &entry, NULL,
574                                   &is_linux);
575     }
576     /* On aarch64, it's the bootloader's job to uncompress the kernel. */
577     if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64) && kernel_size < 0) {
578         entry = info->loader_start + kernel_load_offset;
579         kernel_size = load_image_gzipped(info->kernel_filename, entry,
580                                          info->ram_size - kernel_load_offset);
581         is_linux = 1;
582     }
583     if (kernel_size < 0) {
584         entry = info->loader_start + kernel_load_offset;
585         kernel_size = load_image_targphys(info->kernel_filename, entry,
586                                           info->ram_size - kernel_load_offset);
587         is_linux = 1;
588     }
589     if (kernel_size < 0) {
590         fprintf(stderr, "qemu: could not load kernel '%s'\n",
591                 info->kernel_filename);
592         exit(1);
593     }
594     info->entry = entry;
595     if (is_linux) {
596         uint32_t fixupcontext[FIXUP_MAX];
597 
598         if (info->initrd_filename) {
599             initrd_size = load_ramdisk(info->initrd_filename,
600                                        info->initrd_start,
601                                        info->ram_size -
602                                        info->initrd_start);
603             if (initrd_size < 0) {
604                 initrd_size = load_image_targphys(info->initrd_filename,
605                                                   info->initrd_start,
606                                                   info->ram_size -
607                                                   info->initrd_start);
608             }
609             if (initrd_size < 0) {
610                 fprintf(stderr, "qemu: could not load initrd '%s'\n",
611                         info->initrd_filename);
612                 exit(1);
613             }
614         } else {
615             initrd_size = 0;
616         }
617         info->initrd_size = initrd_size;
618 
619         fixupcontext[FIXUP_BOARDID] = info->board_id;
620 
621         /* for device tree boot, we pass the DTB directly in r2. Otherwise
622          * we point to the kernel args.
623          */
624         if (have_dtb(info)) {
625             /* Place the DTB after the initrd in memory. Note that some
626              * kernels will trash anything in the 4K page the initrd
627              * ends in, so make sure the DTB isn't caught up in that.
628              */
629             hwaddr dtb_start = QEMU_ALIGN_UP(info->initrd_start + initrd_size,
630                                              4096);
631             if (load_dtb(dtb_start, info, 0) < 0) {
632                 exit(1);
633             }
634             fixupcontext[FIXUP_ARGPTR] = dtb_start;
635         } else {
636             fixupcontext[FIXUP_ARGPTR] = info->loader_start + KERNEL_ARGS_ADDR;
637             if (info->ram_size >= (1ULL << 32)) {
638                 fprintf(stderr, "qemu: RAM size must be less than 4GB to boot"
639                         " Linux kernel using ATAGS (try passing a device tree"
640                         " using -dtb)\n");
641                 exit(1);
642             }
643         }
644         fixupcontext[FIXUP_ENTRYPOINT] = entry;
645 
646         write_bootloader("bootloader", info->loader_start,
647                          primary_loader, fixupcontext);
648 
649         if (info->nb_cpus > 1) {
650             info->write_secondary_boot(cpu, info);
651         }
652     }
653     info->is_linux = is_linux;
654 
655     for (; cs; cs = CPU_NEXT(cs)) {
656         cpu = ARM_CPU(cs);
657         cpu->env.boot_info = info;
658         qemu_register_reset(do_cpu_reset, cpu);
659     }
660 }
661