xref: /qemu/semihosting/arm-compat-semi.c (revision b2a3cbb8)
1 /*
2  *  Semihosting support for systems modeled on the Arm "Angel"
3  *  semihosting syscalls design. This includes Arm and RISC-V processors
4  *
5  *  Copyright (c) 2005, 2007 CodeSourcery.
6  *  Copyright (c) 2019 Linaro
7  *  Written by Paul Brook.
8  *
9  *  Copyright © 2020 by Keith Packard <keithp@keithp.com>
10  *  Adapted for systems other than ARM, including RISC-V, by Keith Packard
11  *
12  *  This program is free software; you can redistribute it and/or modify
13  *  it under the terms of the GNU General Public License as published by
14  *  the Free Software Foundation; either version 2 of the License, or
15  *  (at your option) any later version.
16  *
17  *  This program is distributed in the hope that it will be useful,
18  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
19  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
20  *  GNU General Public License for more details.
21  *
22  *  You should have received a copy of the GNU General Public License
23  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
24  *
25  *  ARM Semihosting is documented in:
26  *     Semihosting for AArch32 and AArch64 Release 2.0
27  *     https://github.com/ARM-software/abi-aa/blob/main/semihosting/semihosting.rst
28  *
29  *  RISC-V Semihosting is documented in:
30  *     RISC-V Semihosting
31  *     https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
32  */
33 
34 #include "qemu/osdep.h"
35 #include "qemu/timer.h"
36 #include "exec/gdbstub.h"
37 #include "semihosting/semihost.h"
38 #include "semihosting/console.h"
39 #include "semihosting/common-semi.h"
40 #include "semihosting/guestfd.h"
41 #include "semihosting/syscalls.h"
42 
43 #ifdef CONFIG_USER_ONLY
44 #include "qemu.h"
45 
46 #define COMMON_SEMI_HEAP_SIZE (128 * 1024 * 1024)
47 #else
48 #include "qemu/cutils.h"
49 #include "hw/loader.h"
50 #include "hw/boards.h"
51 #endif
52 
53 #define TARGET_SYS_OPEN        0x01
54 #define TARGET_SYS_CLOSE       0x02
55 #define TARGET_SYS_WRITEC      0x03
56 #define TARGET_SYS_WRITE0      0x04
57 #define TARGET_SYS_WRITE       0x05
58 #define TARGET_SYS_READ        0x06
59 #define TARGET_SYS_READC       0x07
60 #define TARGET_SYS_ISERROR     0x08
61 #define TARGET_SYS_ISTTY       0x09
62 #define TARGET_SYS_SEEK        0x0a
63 #define TARGET_SYS_FLEN        0x0c
64 #define TARGET_SYS_TMPNAM      0x0d
65 #define TARGET_SYS_REMOVE      0x0e
66 #define TARGET_SYS_RENAME      0x0f
67 #define TARGET_SYS_CLOCK       0x10
68 #define TARGET_SYS_TIME        0x11
69 #define TARGET_SYS_SYSTEM      0x12
70 #define TARGET_SYS_ERRNO       0x13
71 #define TARGET_SYS_GET_CMDLINE 0x15
72 #define TARGET_SYS_HEAPINFO    0x16
73 #define TARGET_SYS_EXIT        0x18
74 #define TARGET_SYS_SYNCCACHE   0x19
75 #define TARGET_SYS_EXIT_EXTENDED 0x20
76 #define TARGET_SYS_ELAPSED     0x30
77 #define TARGET_SYS_TICKFREQ    0x31
78 
79 /* ADP_Stopped_ApplicationExit is used for exit(0),
80  * anything else is implemented as exit(1) */
81 #define ADP_Stopped_ApplicationExit     (0x20026)
82 
83 #ifndef O_BINARY
84 #define O_BINARY 0
85 #endif
86 
87 static int gdb_open_modeflags[12] = {
88     GDB_O_RDONLY,
89     GDB_O_RDONLY,
90     GDB_O_RDWR,
91     GDB_O_RDWR,
92     GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC,
93     GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC,
94     GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC,
95     GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC,
96     GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND,
97     GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND,
98     GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND,
99     GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND,
100 };
101 
102 #ifndef CONFIG_USER_ONLY
103 
104 /**
105  * common_semi_find_bases: find information about ram and heap base
106  *
107  * This function attempts to provide meaningful numbers for RAM and
108  * HEAP base addresses. The rambase is simply the lowest addressable
109  * RAM position. For the heapbase we ask the loader to scan the
110  * address space and the largest available gap by querying the "ROM"
111  * regions.
112  *
113  * Returns: a structure with the numbers we need.
114  */
115 
116 typedef struct LayoutInfo {
117     target_ulong rambase;
118     size_t ramsize;
119     hwaddr heapbase;
120     hwaddr heaplimit;
121 } LayoutInfo;
122 
123 static bool find_ram_cb(Int128 start, Int128 len, const MemoryRegion *mr,
124                         hwaddr offset_in_region, void *opaque)
125 {
126     LayoutInfo *info = (LayoutInfo *) opaque;
127     uint64_t size = int128_get64(len);
128 
129     if (!mr->ram || mr->readonly) {
130         return false;
131     }
132 
133     if (size > info->ramsize) {
134         info->rambase = int128_get64(start);
135         info->ramsize = size;
136     }
137 
138     /* search exhaustively for largest RAM */
139     return false;
140 }
141 
142 static LayoutInfo common_semi_find_bases(CPUState *cs)
143 {
144     FlatView *fv;
145     LayoutInfo info = { 0, 0, 0, 0 };
146 
147     RCU_READ_LOCK_GUARD();
148 
149     fv = address_space_to_flatview(cs->as);
150     flatview_for_each_range(fv, find_ram_cb, &info);
151 
152     /*
153      * If we have found the RAM lets iterate through the ROM blobs to
154      * work out the best place for the remainder of RAM and split it
155      * equally between stack and heap.
156      */
157     if (info.rambase || info.ramsize > 0) {
158         RomGap gap = rom_find_largest_gap_between(info.rambase, info.ramsize);
159         info.heapbase = gap.base;
160         info.heaplimit = gap.base + gap.size;
161     }
162 
163     return info;
164 }
165 
166 #endif
167 
168 #include "common-semi-target.h"
169 
170 /*
171  * Read the input value from the argument block; fail the semihosting
172  * call if the memory read fails. Eventually we could use a generic
173  * CPUState helper function here.
174  * Note that GET_ARG() handles memory access errors by jumping to
175  * do_fault, so must be used as the first thing done in handling a
176  * semihosting call, to avoid accidentally leaking allocated resources.
177  * SET_ARG(), since it unavoidably happens late, instead returns an
178  * error indication (0 on success, non-0 for error) which the caller
179  * should check.
180  */
181 
182 #define GET_ARG(n) do {                                 \
183     if (is_64bit_semihosting(env)) {                    \
184         if (get_user_u64(arg ## n, args + (n) * 8)) {   \
185             goto do_fault;                              \
186         }                                               \
187     } else {                                            \
188         if (get_user_u32(arg ## n, args + (n) * 4)) {   \
189             goto do_fault;                              \
190         }                                               \
191     }                                                   \
192 } while (0)
193 
194 #define SET_ARG(n, val)                                 \
195     (is_64bit_semihosting(env) ?                        \
196      put_user_u64(val, args + (n) * 8) :                \
197      put_user_u32(val, args + (n) * 4))
198 
199 
200 /*
201  * The semihosting API has no concept of its errno being thread-safe,
202  * as the API design predates SMP CPUs and was intended as a simple
203  * real-hardware set of debug functionality. For QEMU, we make the
204  * errno be per-thread in linux-user mode; in softmmu it is a simple
205  * global, and we assume that the guest takes care of avoiding any races.
206  */
207 #ifndef CONFIG_USER_ONLY
208 static target_ulong syscall_err;
209 
210 #include "semihosting/softmmu-uaccess.h"
211 #endif
212 
213 static inline uint32_t get_swi_errno(CPUState *cs)
214 {
215 #ifdef CONFIG_USER_ONLY
216     TaskState *ts = cs->opaque;
217 
218     return ts->swi_errno;
219 #else
220     return syscall_err;
221 #endif
222 }
223 
224 static void common_semi_cb(CPUState *cs, uint64_t ret, int err)
225 {
226     if (err) {
227 #ifdef CONFIG_USER_ONLY
228         TaskState *ts = cs->opaque;
229         ts->swi_errno = err;
230 #else
231         syscall_err = err;
232 #endif
233     }
234     common_semi_set_ret(cs, ret);
235 }
236 
237 /*
238  * Use 0xdeadbeef as the return value when there isn't a defined
239  * return value for the call.
240  */
241 static void common_semi_dead_cb(CPUState *cs, uint64_t ret, int err)
242 {
243     common_semi_set_ret(cs, 0xdeadbeef);
244 }
245 
246 /*
247  * SYS_READ and SYS_WRITE always return the number of bytes not read/written.
248  * There is no error condition, other than returning the original length.
249  */
250 static void common_semi_rw_cb(CPUState *cs, uint64_t ret, int err)
251 {
252     /* Recover the original length from the third argument. */
253     CPUArchState *env G_GNUC_UNUSED = cs->env_ptr;
254     target_ulong args = common_semi_arg(cs, 1);
255     target_ulong arg2;
256     GET_ARG(2);
257 
258     if (err) {
259  do_fault:
260         ret = 0; /* error: no bytes transmitted */
261     }
262     common_semi_set_ret(cs, arg2 - ret);
263 }
264 
265 /*
266  * Convert from Posix ret+errno to Arm SYS_ISTTY return values.
267  * With gdbstub, err is only ever set for protocol errors to EIO.
268  */
269 static void common_semi_istty_cb(CPUState *cs, uint64_t ret, int err)
270 {
271     if (err) {
272         ret = (err == ENOTTY ? 0 : -1);
273     }
274     common_semi_cb(cs, ret, err);
275 }
276 
277 /*
278  * SYS_SEEK returns 0 on success, not the resulting offset.
279  */
280 static void common_semi_seek_cb(CPUState *cs, uint64_t ret, int err)
281 {
282     if (!err) {
283         ret = 0;
284     }
285     common_semi_cb(cs, ret, err);
286 }
287 
288 /*
289  * Return an address in target memory of 64 bytes where the remote
290  * gdb should write its stat struct. (The format of this structure
291  * is defined by GDB's remote protocol and is not target-specific.)
292  * We put this on the guest's stack just below SP.
293  */
294 static target_ulong common_semi_flen_buf(CPUState *cs)
295 {
296     target_ulong sp = common_semi_stack_bottom(cs);
297     return sp - 64;
298 }
299 
300 static void
301 common_semi_flen_fstat_cb(CPUState *cs, uint64_t ret, int err)
302 {
303     if (!err) {
304         /* The size is always stored in big-endian order, extract the value. */
305         uint64_t size;
306         if (cpu_memory_rw_debug(cs, common_semi_flen_buf(cs) +
307                                 offsetof(struct gdb_stat, gdb_st_size),
308                                 &size, 8, 0)) {
309             ret = -1, err = EFAULT;
310         } else {
311             size = be64_to_cpu(size);
312             if (ret != size) {
313                 ret = -1, err = EOVERFLOW;
314             }
315         }
316     }
317     common_semi_cb(cs, ret, err);
318 }
319 
320 static void
321 common_semi_readc_cb(CPUState *cs, uint64_t ret, int err)
322 {
323     if (!err) {
324         CPUArchState *env G_GNUC_UNUSED = cs->env_ptr;
325         uint8_t ch;
326 
327         if (get_user_u8(ch, common_semi_stack_bottom(cs) - 1)) {
328             ret = -1, err = EFAULT;
329         } else {
330             ret = ch;
331         }
332     }
333     common_semi_cb(cs, ret, err);
334 }
335 
336 #define SHFB_MAGIC_0 0x53
337 #define SHFB_MAGIC_1 0x48
338 #define SHFB_MAGIC_2 0x46
339 #define SHFB_MAGIC_3 0x42
340 
341 /* Feature bits reportable in feature byte 0 */
342 #define SH_EXT_EXIT_EXTENDED (1 << 0)
343 #define SH_EXT_STDOUT_STDERR (1 << 1)
344 
345 static const uint8_t featurefile_data[] = {
346     SHFB_MAGIC_0,
347     SHFB_MAGIC_1,
348     SHFB_MAGIC_2,
349     SHFB_MAGIC_3,
350     SH_EXT_EXIT_EXTENDED | SH_EXT_STDOUT_STDERR, /* Feature byte 0 */
351 };
352 
353 /*
354  * Do a semihosting call.
355  *
356  * The specification always says that the "return register" either
357  * returns a specific value or is corrupted, so we don't need to
358  * report to our caller whether we are returning a value or trying to
359  * leave the register unchanged.
360  */
361 void do_common_semihosting(CPUState *cs)
362 {
363     CPUArchState *env = cs->env_ptr;
364     target_ulong args;
365     target_ulong arg0, arg1, arg2, arg3;
366     target_ulong ul_ret;
367     char * s;
368     int nr;
369     uint32_t ret;
370     int64_t elapsed;
371 
372     nr = common_semi_arg(cs, 0) & 0xffffffffU;
373     args = common_semi_arg(cs, 1);
374 
375     switch (nr) {
376     case TARGET_SYS_OPEN:
377     {
378         int ret, err = 0;
379         int hostfd;
380 
381         GET_ARG(0);
382         GET_ARG(1);
383         GET_ARG(2);
384         s = lock_user_string(arg0);
385         if (!s) {
386             goto do_fault;
387         }
388         if (arg1 >= 12) {
389             unlock_user(s, arg0, 0);
390             common_semi_cb(cs, -1, EINVAL);
391             break;
392         }
393 
394         if (strcmp(s, ":tt") == 0) {
395             /*
396              * We implement SH_EXT_STDOUT_STDERR, so:
397              *  open for read == stdin
398              *  open for write == stdout
399              *  open for append == stderr
400              */
401             if (arg1 < 4) {
402                 hostfd = STDIN_FILENO;
403             } else if (arg1 < 8) {
404                 hostfd = STDOUT_FILENO;
405             } else {
406                 hostfd = STDERR_FILENO;
407             }
408             ret = alloc_guestfd();
409             associate_guestfd(ret, hostfd);
410         } else if (strcmp(s, ":semihosting-features") == 0) {
411             /* We must fail opens for modes other than 0 ('r') or 1 ('rb') */
412             if (arg1 != 0 && arg1 != 1) {
413                 ret = -1;
414                 err = EACCES;
415             } else {
416                 ret = alloc_guestfd();
417                 staticfile_guestfd(ret, featurefile_data,
418                                    sizeof(featurefile_data));
419             }
420         } else {
421             unlock_user(s, arg0, 0);
422             semihost_sys_open(cs, common_semi_cb, arg0, arg2 + 1,
423                               gdb_open_modeflags[arg1], 0644);
424             break;
425         }
426         unlock_user(s, arg0, 0);
427         common_semi_cb(cs, ret, err);
428         break;
429     }
430 
431     case TARGET_SYS_CLOSE:
432         GET_ARG(0);
433         semihost_sys_close(cs, common_semi_cb, arg0);
434         break;
435 
436     case TARGET_SYS_WRITEC:
437         /*
438          * FIXME: the byte to be written is in a target_ulong slot,
439          * which means this is wrong for a big-endian guest.
440          */
441         semihost_sys_write_gf(cs, common_semi_dead_cb,
442                               &console_out_gf, args, 1);
443         break;
444 
445     case TARGET_SYS_WRITE0:
446         {
447             ssize_t len = target_strlen(args);
448             if (len < 0) {
449                 common_semi_dead_cb(cs, -1, EFAULT);
450             } else {
451                 semihost_sys_write_gf(cs, common_semi_dead_cb,
452                                       &console_out_gf, args, len);
453             }
454         }
455         break;
456 
457     case TARGET_SYS_WRITE:
458         GET_ARG(0);
459         GET_ARG(1);
460         GET_ARG(2);
461         semihost_sys_write(cs, common_semi_rw_cb, arg0, arg1, arg2);
462         break;
463 
464     case TARGET_SYS_READ:
465         GET_ARG(0);
466         GET_ARG(1);
467         GET_ARG(2);
468         semihost_sys_read(cs, common_semi_rw_cb, arg0, arg1, arg2);
469         break;
470 
471     case TARGET_SYS_READC:
472         semihost_sys_read_gf(cs, common_semi_readc_cb, &console_in_gf,
473                              common_semi_stack_bottom(cs) - 1, 1);
474         break;
475 
476     case TARGET_SYS_ISERROR:
477         GET_ARG(0);
478         common_semi_set_ret(cs, (target_long)arg0 < 0);
479         break;
480 
481     case TARGET_SYS_ISTTY:
482         GET_ARG(0);
483         semihost_sys_isatty(cs, common_semi_istty_cb, arg0);
484         break;
485 
486     case TARGET_SYS_SEEK:
487         GET_ARG(0);
488         GET_ARG(1);
489         semihost_sys_lseek(cs, common_semi_seek_cb, arg0, arg1, GDB_SEEK_SET);
490         break;
491 
492     case TARGET_SYS_FLEN:
493         GET_ARG(0);
494         semihost_sys_flen(cs, common_semi_flen_fstat_cb, common_semi_cb,
495                           arg0, common_semi_flen_buf(cs));
496         break;
497 
498     case TARGET_SYS_TMPNAM:
499     {
500         int len;
501         char *p;
502 
503         GET_ARG(0);
504         GET_ARG(1);
505         GET_ARG(2);
506         len = asprintf(&s, "%s/qemu-%x%02x", g_get_tmp_dir(),
507                        getpid(), (int)arg1 & 0xff);
508         if (len < 0) {
509             common_semi_set_ret(cs, -1);
510             break;
511         }
512 
513         /* Allow for trailing NUL */
514         len++;
515         /* Make sure there's enough space in the buffer */
516         if (len > arg2) {
517             free(s);
518             common_semi_set_ret(cs, -1);
519             break;
520         }
521         p = lock_user(VERIFY_WRITE, arg0, len, 0);
522         if (!p) {
523             free(s);
524             goto do_fault;
525         }
526         memcpy(p, s, len);
527         unlock_user(p, arg0, len);
528         free(s);
529         common_semi_set_ret(cs, 0);
530         break;
531     }
532 
533     case TARGET_SYS_REMOVE:
534         GET_ARG(0);
535         GET_ARG(1);
536         semihost_sys_remove(cs, common_semi_cb, arg0, arg1 + 1);
537         break;
538 
539     case TARGET_SYS_RENAME:
540         GET_ARG(0);
541         GET_ARG(1);
542         GET_ARG(2);
543         GET_ARG(3);
544         semihost_sys_rename(cs, common_semi_cb, arg0, arg1 + 1, arg2, arg3 + 1);
545         break;
546 
547     case TARGET_SYS_CLOCK:
548         common_semi_set_ret(cs, clock() / (CLOCKS_PER_SEC / 100));
549         break;
550 
551     case TARGET_SYS_TIME:
552         ul_ret = time(NULL);
553         common_semi_cb(cs, ul_ret, ul_ret == -1 ? errno : 0);
554         break;
555 
556     case TARGET_SYS_SYSTEM:
557         GET_ARG(0);
558         GET_ARG(1);
559         semihost_sys_system(cs, common_semi_cb, arg0, arg1 + 1);
560         break;
561 
562     case TARGET_SYS_ERRNO:
563         common_semi_set_ret(cs, get_swi_errno(cs));
564         break;
565 
566     case TARGET_SYS_GET_CMDLINE:
567         {
568             /* Build a command-line from the original argv.
569              *
570              * The inputs are:
571              *     * arg0, pointer to a buffer of at least the size
572              *               specified in arg1.
573              *     * arg1, size of the buffer pointed to by arg0 in
574              *               bytes.
575              *
576              * The outputs are:
577              *     * arg0, pointer to null-terminated string of the
578              *               command line.
579              *     * arg1, length of the string pointed to by arg0.
580              */
581 
582             char *output_buffer;
583             size_t input_size;
584             size_t output_size;
585             int status = 0;
586 #if !defined(CONFIG_USER_ONLY)
587             const char *cmdline;
588 #else
589             TaskState *ts = cs->opaque;
590 #endif
591             GET_ARG(0);
592             GET_ARG(1);
593             input_size = arg1;
594             /* Compute the size of the output string.  */
595 #if !defined(CONFIG_USER_ONLY)
596             cmdline = semihosting_get_cmdline();
597             if (cmdline == NULL) {
598                 cmdline = ""; /* Default to an empty line. */
599             }
600             output_size = strlen(cmdline) + 1; /* Count terminating 0. */
601 #else
602             unsigned int i;
603 
604             output_size = ts->info->env_strings - ts->info->arg_strings;
605             if (!output_size) {
606                 /*
607                  * We special-case the "empty command line" case (argc==0).
608                  * Just provide the terminating 0.
609                  */
610                 output_size = 1;
611             }
612 #endif
613 
614             if (output_size > input_size) {
615                 /* Not enough space to store command-line arguments.  */
616                 common_semi_cb(cs, -1, E2BIG);
617                 break;
618             }
619 
620             /* Adjust the command-line length.  */
621             if (SET_ARG(1, output_size - 1)) {
622                 /* Couldn't write back to argument block */
623                 goto do_fault;
624             }
625 
626             /* Lock the buffer on the ARM side.  */
627             output_buffer = lock_user(VERIFY_WRITE, arg0, output_size, 0);
628             if (!output_buffer) {
629                 goto do_fault;
630             }
631 
632             /* Copy the command-line arguments.  */
633 #if !defined(CONFIG_USER_ONLY)
634             pstrcpy(output_buffer, output_size, cmdline);
635 #else
636             if (output_size == 1) {
637                 /* Empty command-line.  */
638                 output_buffer[0] = '\0';
639                 goto out;
640             }
641 
642             if (copy_from_user(output_buffer, ts->info->arg_strings,
643                                output_size)) {
644                 unlock_user(output_buffer, arg0, 0);
645                 goto do_fault;
646             }
647 
648             /* Separate arguments by white spaces.  */
649             for (i = 0; i < output_size - 1; i++) {
650                 if (output_buffer[i] == 0) {
651                     output_buffer[i] = ' ';
652                 }
653             }
654         out:
655 #endif
656             /* Unlock the buffer on the ARM side.  */
657             unlock_user(output_buffer, arg0, output_size);
658             common_semi_cb(cs, status, 0);
659         }
660         break;
661 
662     case TARGET_SYS_HEAPINFO:
663         {
664             target_ulong retvals[4];
665             int i;
666 #ifdef CONFIG_USER_ONLY
667             TaskState *ts = cs->opaque;
668             target_ulong limit;
669 #else
670             LayoutInfo info = common_semi_find_bases(cs);
671 #endif
672 
673             GET_ARG(0);
674 
675 #ifdef CONFIG_USER_ONLY
676             /*
677              * Some C libraries assume the heap immediately follows .bss, so
678              * allocate it using sbrk.
679              */
680             if (!ts->heap_limit) {
681                 abi_ulong ret;
682 
683                 ts->heap_base = do_brk(0);
684                 limit = ts->heap_base + COMMON_SEMI_HEAP_SIZE;
685                 /* Try a big heap, and reduce the size if that fails.  */
686                 for (;;) {
687                     ret = do_brk(limit);
688                     if (ret >= limit) {
689                         break;
690                     }
691                     limit = (ts->heap_base >> 1) + (limit >> 1);
692                 }
693                 ts->heap_limit = limit;
694             }
695 
696             retvals[0] = ts->heap_base;
697             retvals[1] = ts->heap_limit;
698             retvals[2] = ts->stack_base;
699             retvals[3] = 0; /* Stack limit.  */
700 #else
701             retvals[0] = info.heapbase;  /* Heap Base */
702             retvals[1] = info.heaplimit; /* Heap Limit */
703             retvals[2] = info.heaplimit; /* Stack base */
704             retvals[3] = info.heapbase;  /* Stack limit.  */
705 #endif
706 
707             for (i = 0; i < ARRAY_SIZE(retvals); i++) {
708                 bool fail;
709 
710                 if (is_64bit_semihosting(env)) {
711                     fail = put_user_u64(retvals[i], arg0 + i * 8);
712                 } else {
713                     fail = put_user_u32(retvals[i], arg0 + i * 4);
714                 }
715 
716                 if (fail) {
717                     /* Couldn't write back to argument block */
718                     goto do_fault;
719                 }
720             }
721             common_semi_set_ret(cs, 0);
722         }
723         break;
724 
725     case TARGET_SYS_EXIT:
726     case TARGET_SYS_EXIT_EXTENDED:
727         if (common_semi_sys_exit_extended(cs, nr)) {
728             /*
729              * The A64 version of SYS_EXIT takes a parameter block,
730              * so the application-exit type can return a subcode which
731              * is the exit status code from the application.
732              * SYS_EXIT_EXTENDED is an a new-in-v2.0 optional function
733              * which allows A32/T32 guests to also provide a status code.
734              */
735             GET_ARG(0);
736             GET_ARG(1);
737 
738             if (arg0 == ADP_Stopped_ApplicationExit) {
739                 ret = arg1;
740             } else {
741                 ret = 1;
742             }
743         } else {
744             /*
745              * The A32/T32 version of SYS_EXIT specifies only
746              * Stopped_ApplicationExit as normal exit, but does not
747              * allow the guest to specify the exit status code.
748              * Everything else is considered an error.
749              */
750             ret = (args == ADP_Stopped_ApplicationExit) ? 0 : 1;
751         }
752         gdb_exit(ret);
753         exit(ret);
754 
755     case TARGET_SYS_ELAPSED:
756         elapsed = get_clock() - clock_start;
757         if (sizeof(target_ulong) == 8) {
758             if (SET_ARG(0, elapsed)) {
759                 goto do_fault;
760             }
761         } else {
762             if (SET_ARG(0, (uint32_t) elapsed) ||
763                 SET_ARG(1, (uint32_t) (elapsed >> 32))) {
764                 goto do_fault;
765             }
766         }
767         common_semi_set_ret(cs, 0);
768         break;
769 
770     case TARGET_SYS_TICKFREQ:
771         /* qemu always uses nsec */
772         common_semi_set_ret(cs, 1000000000);
773         break;
774 
775     case TARGET_SYS_SYNCCACHE:
776         /*
777          * Clean the D-cache and invalidate the I-cache for the specified
778          * virtual address range. This is a nop for us since we don't
779          * implement caches. This is only present on A64.
780          */
781         if (common_semi_has_synccache(env)) {
782             common_semi_set_ret(cs, 0);
783             break;
784         }
785         /* fall through */
786     default:
787         fprintf(stderr, "qemu: Unsupported SemiHosting SWI 0x%02x\n", nr);
788         cpu_dump_state(cs, stderr, 0);
789         abort();
790 
791     do_fault:
792         common_semi_cb(cs, -1, EFAULT);
793         break;
794     }
795 }
796