xref: /openbmc/qemu/linux-user/arm/signal.c (revision e6203636)
1 /*
2  *  Emulation of Linux signals
3  *
4  *  Copyright (c) 2003 Fabrice Bellard
5  *
6  *  This program is free software; you can redistribute it and/or modify
7  *  it under the terms of the GNU General Public License as published by
8  *  the Free Software Foundation; either version 2 of the License, or
9  *  (at your option) any later version.
10  *
11  *  This program is distributed in the hope that it will be useful,
12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  *  GNU General Public License for more details.
15  *
16  *  You should have received a copy of the GNU General Public License
17  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
18  */
19 #include "qemu/osdep.h"
20 #include "qemu.h"
21 #include "user-internals.h"
22 #include "signal-common.h"
23 #include "linux-user/trace.h"
24 #include "target/arm/cpu-features.h"
25 #include "vdso-asmoffset.h"
26 
27 struct target_sigcontext {
28     abi_ulong trap_no;
29     abi_ulong error_code;
30     abi_ulong oldmask;
31     abi_ulong arm_r0;
32     abi_ulong arm_r1;
33     abi_ulong arm_r2;
34     abi_ulong arm_r3;
35     abi_ulong arm_r4;
36     abi_ulong arm_r5;
37     abi_ulong arm_r6;
38     abi_ulong arm_r7;
39     abi_ulong arm_r8;
40     abi_ulong arm_r9;
41     abi_ulong arm_r10;
42     abi_ulong arm_fp;
43     abi_ulong arm_ip;
44     abi_ulong arm_sp;
45     abi_ulong arm_lr;
46     abi_ulong arm_pc;
47     abi_ulong arm_cpsr;
48     abi_ulong fault_address;
49 };
50 
51 struct target_ucontext {
52     abi_ulong tuc_flags;
53     abi_ulong tuc_link;
54     target_stack_t tuc_stack;
55     struct target_sigcontext tuc_mcontext;
56     target_sigset_t  tuc_sigmask;       /* mask last for extensibility */
57     char __unused[128 - sizeof(target_sigset_t)];
58     abi_ulong tuc_regspace[128] __attribute__((__aligned__(8)));
59 };
60 
61 struct target_user_vfp {
62     uint64_t fpregs[32];
63     abi_ulong fpscr;
64 };
65 
66 struct target_user_vfp_exc {
67     abi_ulong fpexc;
68     abi_ulong fpinst;
69     abi_ulong fpinst2;
70 };
71 
72 struct target_vfp_sigframe {
73     abi_ulong magic;
74     abi_ulong size;
75     struct target_user_vfp ufp;
76     struct target_user_vfp_exc ufp_exc;
77 } __attribute__((__aligned__(8)));
78 
79 struct target_iwmmxt_sigframe {
80     abi_ulong magic;
81     abi_ulong size;
82     uint64_t regs[16];
83     /* Note that not all the coprocessor control registers are stored here */
84     uint32_t wcssf;
85     uint32_t wcasf;
86     uint32_t wcgr0;
87     uint32_t wcgr1;
88     uint32_t wcgr2;
89     uint32_t wcgr3;
90 } __attribute__((__aligned__(8)));
91 
92 #define TARGET_VFP_MAGIC 0x56465001
93 #define TARGET_IWMMXT_MAGIC 0x12ef842a
94 
95 struct sigframe
96 {
97     struct target_ucontext uc;
98     abi_ulong retcode[4];
99 };
100 
101 struct rt_sigframe
102 {
103     struct target_siginfo info;
104     struct sigframe sig;
105 };
106 
107 QEMU_BUILD_BUG_ON(offsetof(struct sigframe, retcode[3])
108                   != SIGFRAME_RC3_OFFSET);
109 QEMU_BUILD_BUG_ON(offsetof(struct rt_sigframe, sig.retcode[3])
110                   != RT_SIGFRAME_RC3_OFFSET);
111 
112 static abi_ptr sigreturn_fdpic_tramp;
113 
114 /*
115  * Up to 3 words of 'retcode' in the sigframe are code,
116  * with retcode[3] being used by fdpic for the function descriptor.
117  * This code is not actually executed, but is retained for ABI compat.
118  *
119  * We will create a table of 8 retcode variants in the sigtramp page.
120  * Let each table entry use 3 words.
121  */
122 #define RETCODE_WORDS  3
123 #define RETCODE_BYTES  (RETCODE_WORDS * 4)
124 
125 static inline int valid_user_regs(CPUARMState *regs)
126 {
127     return 1;
128 }
129 
130 static void
131 setup_sigcontext(struct target_sigcontext *sc, /*struct _fpstate *fpstate,*/
132                  CPUARMState *env, abi_ulong mask)
133 {
134     __put_user(env->regs[0], &sc->arm_r0);
135     __put_user(env->regs[1], &sc->arm_r1);
136     __put_user(env->regs[2], &sc->arm_r2);
137     __put_user(env->regs[3], &sc->arm_r3);
138     __put_user(env->regs[4], &sc->arm_r4);
139     __put_user(env->regs[5], &sc->arm_r5);
140     __put_user(env->regs[6], &sc->arm_r6);
141     __put_user(env->regs[7], &sc->arm_r7);
142     __put_user(env->regs[8], &sc->arm_r8);
143     __put_user(env->regs[9], &sc->arm_r9);
144     __put_user(env->regs[10], &sc->arm_r10);
145     __put_user(env->regs[11], &sc->arm_fp);
146     __put_user(env->regs[12], &sc->arm_ip);
147     __put_user(env->regs[13], &sc->arm_sp);
148     __put_user(env->regs[14], &sc->arm_lr);
149     __put_user(env->regs[15], &sc->arm_pc);
150     __put_user(cpsr_read(env), &sc->arm_cpsr);
151 
152     __put_user(/* current->thread.trap_no */ 0, &sc->trap_no);
153     __put_user(/* current->thread.error_code */ 0, &sc->error_code);
154     __put_user(/* current->thread.address */ 0, &sc->fault_address);
155     __put_user(mask, &sc->oldmask);
156 }
157 
158 static inline abi_ulong
159 get_sigframe(struct target_sigaction *ka, CPUARMState *regs, int framesize)
160 {
161     unsigned long sp;
162 
163     sp = target_sigsp(get_sp_from_cpustate(regs), ka);
164     /*
165      * ATPCS B01 mandates 8-byte alignment
166      */
167     return (sp - framesize) & ~7;
168 }
169 
170 static void write_arm_sigreturn(uint32_t *rc, int syscall);
171 static void write_arm_fdpic_sigreturn(uint32_t *rc, int ofs);
172 
173 static int
174 setup_return(CPUARMState *env, struct target_sigaction *ka, int usig,
175              struct sigframe *frame, abi_ulong sp_addr)
176 {
177     abi_ulong handler = 0;
178     abi_ulong handler_fdpic_GOT = 0;
179     abi_ulong retcode;
180     bool is_fdpic = info_is_fdpic(get_task_state(thread_cpu)->info);
181     bool is_rt = ka->sa_flags & TARGET_SA_SIGINFO;
182     bool thumb;
183 
184     if (is_fdpic) {
185         /* In FDPIC mode, ka->_sa_handler points to a function
186          * descriptor (FD). The first word contains the address of the
187          * handler. The second word contains the value of the PIC
188          * register (r9).  */
189         abi_ulong funcdesc_ptr = ka->_sa_handler;
190         if (get_user_ual(handler, funcdesc_ptr)
191             || get_user_ual(handler_fdpic_GOT, funcdesc_ptr + 4)) {
192             return 1;
193         }
194     } else {
195         handler = ka->_sa_handler;
196     }
197     thumb = handler & 1;
198 
199     uint32_t cpsr = cpsr_read(env);
200 
201     cpsr &= ~CPSR_IT;
202     if (thumb) {
203         cpsr |= CPSR_T;
204     } else {
205         cpsr &= ~CPSR_T;
206     }
207     if (env->cp15.sctlr_el[1] & SCTLR_E0E) {
208         cpsr |= CPSR_E;
209     } else {
210         cpsr &= ~CPSR_E;
211     }
212 
213     /* Our vdso default_sigreturn label is a table of entry points. */
214     retcode = default_sigreturn + (is_fdpic * 2 + is_rt) * 8;
215 
216     /*
217      * Put the sigreturn code on the stack no matter which return
218      * mechanism we use in order to remain ABI compliant.
219      * Because this is about ABI, always use the A32 instructions,
220      * despite the fact that our actual vdso trampoline is T16.
221      */
222     if (is_fdpic) {
223         write_arm_fdpic_sigreturn(frame->retcode,
224                                   is_rt ? RT_SIGFRAME_RC3_OFFSET
225                                         : SIGFRAME_RC3_OFFSET);
226     } else {
227         write_arm_sigreturn(frame->retcode,
228                             is_rt ? TARGET_NR_rt_sigreturn
229                                   : TARGET_NR_sigreturn);
230     }
231 
232     if (ka->sa_flags & TARGET_SA_RESTORER) {
233         if (is_fdpic) {
234             /* Place the function descriptor in slot 3. */
235             __put_user((abi_ulong)ka->sa_restorer, &frame->retcode[3]);
236         } else {
237             retcode = ka->sa_restorer;
238         }
239     }
240 
241     env->regs[0] = usig;
242     if (is_fdpic) {
243         env->regs[9] = handler_fdpic_GOT;
244     }
245     env->regs[13] = sp_addr;
246     env->regs[14] = retcode;
247     env->regs[15] = handler & (thumb ? ~1 : ~3);
248     cpsr_write(env, cpsr, CPSR_IT | CPSR_T | CPSR_E, CPSRWriteByInstr);
249 
250     return 0;
251 }
252 
253 static abi_ulong *setup_sigframe_vfp(abi_ulong *regspace, CPUARMState *env)
254 {
255     int i;
256     struct target_vfp_sigframe *vfpframe;
257     vfpframe = (struct target_vfp_sigframe *)regspace;
258     __put_user(TARGET_VFP_MAGIC, &vfpframe->magic);
259     __put_user(sizeof(*vfpframe), &vfpframe->size);
260     for (i = 0; i < 32; i++) {
261         __put_user(*aa32_vfp_dreg(env, i), &vfpframe->ufp.fpregs[i]);
262     }
263     __put_user(vfp_get_fpscr(env), &vfpframe->ufp.fpscr);
264     __put_user(env->vfp.xregs[ARM_VFP_FPEXC], &vfpframe->ufp_exc.fpexc);
265     __put_user(env->vfp.xregs[ARM_VFP_FPINST], &vfpframe->ufp_exc.fpinst);
266     __put_user(env->vfp.xregs[ARM_VFP_FPINST2], &vfpframe->ufp_exc.fpinst2);
267     return (abi_ulong*)(vfpframe+1);
268 }
269 
270 static abi_ulong *setup_sigframe_iwmmxt(abi_ulong *regspace, CPUARMState *env)
271 {
272     int i;
273     struct target_iwmmxt_sigframe *iwmmxtframe;
274     iwmmxtframe = (struct target_iwmmxt_sigframe *)regspace;
275     __put_user(TARGET_IWMMXT_MAGIC, &iwmmxtframe->magic);
276     __put_user(sizeof(*iwmmxtframe), &iwmmxtframe->size);
277     for (i = 0; i < 16; i++) {
278         __put_user(env->iwmmxt.regs[i], &iwmmxtframe->regs[i]);
279     }
280     __put_user(env->vfp.xregs[ARM_IWMMXT_wCSSF], &iwmmxtframe->wcssf);
281     __put_user(env->vfp.xregs[ARM_IWMMXT_wCASF], &iwmmxtframe->wcssf);
282     __put_user(env->vfp.xregs[ARM_IWMMXT_wCGR0], &iwmmxtframe->wcgr0);
283     __put_user(env->vfp.xregs[ARM_IWMMXT_wCGR1], &iwmmxtframe->wcgr1);
284     __put_user(env->vfp.xregs[ARM_IWMMXT_wCGR2], &iwmmxtframe->wcgr2);
285     __put_user(env->vfp.xregs[ARM_IWMMXT_wCGR3], &iwmmxtframe->wcgr3);
286     return (abi_ulong*)(iwmmxtframe+1);
287 }
288 
289 static void setup_sigframe(struct target_ucontext *uc,
290                            target_sigset_t *set, CPUARMState *env)
291 {
292     struct target_sigaltstack stack;
293     int i;
294     abi_ulong *regspace;
295 
296     /* Clear all the bits of the ucontext we don't use.  */
297     memset(uc, 0, offsetof(struct target_ucontext, tuc_mcontext));
298 
299     memset(&stack, 0, sizeof(stack));
300     target_save_altstack(&stack, env);
301     memcpy(&uc->tuc_stack, &stack, sizeof(stack));
302 
303     setup_sigcontext(&uc->tuc_mcontext, env, set->sig[0]);
304     /* Save coprocessor signal frame.  */
305     regspace = uc->tuc_regspace;
306     if (cpu_isar_feature(aa32_vfp_simd, env_archcpu(env))) {
307         regspace = setup_sigframe_vfp(regspace, env);
308     }
309     if (arm_feature(env, ARM_FEATURE_IWMMXT)) {
310         regspace = setup_sigframe_iwmmxt(regspace, env);
311     }
312 
313     /* Write terminating magic word */
314     __put_user(0, regspace);
315 
316     for(i = 0; i < TARGET_NSIG_WORDS; i++) {
317         __put_user(set->sig[i], &uc->tuc_sigmask.sig[i]);
318     }
319 }
320 
321 void setup_frame(int usig, struct target_sigaction *ka,
322                  target_sigset_t *set, CPUARMState *regs)
323 {
324     struct sigframe *frame;
325     abi_ulong frame_addr = get_sigframe(ka, regs, sizeof(*frame));
326 
327     trace_user_setup_frame(regs, frame_addr);
328     if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) {
329         goto sigsegv;
330     }
331 
332     setup_sigframe(&frame->uc, set, regs);
333 
334     if (setup_return(regs, ka, usig, frame, frame_addr)) {
335         goto sigsegv;
336     }
337 
338     unlock_user_struct(frame, frame_addr, 1);
339     return;
340 sigsegv:
341     unlock_user_struct(frame, frame_addr, 1);
342     force_sigsegv(usig);
343 }
344 
345 void setup_rt_frame(int usig, struct target_sigaction *ka,
346                     target_siginfo_t *info,
347                     target_sigset_t *set, CPUARMState *env)
348 {
349     struct rt_sigframe *frame;
350     abi_ulong frame_addr = get_sigframe(ka, env, sizeof(*frame));
351     abi_ulong info_addr, uc_addr;
352 
353     trace_user_setup_rt_frame(env, frame_addr);
354     if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) {
355         goto sigsegv;
356     }
357 
358     info_addr = frame_addr + offsetof(struct rt_sigframe, info);
359     uc_addr = frame_addr + offsetof(struct rt_sigframe, sig.uc);
360     frame->info = *info;
361 
362     setup_sigframe(&frame->sig.uc, set, env);
363 
364     if (setup_return(env, ka, usig, &frame->sig, frame_addr)) {
365         goto sigsegv;
366     }
367 
368     env->regs[1] = info_addr;
369     env->regs[2] = uc_addr;
370 
371     unlock_user_struct(frame, frame_addr, 1);
372     return;
373 sigsegv:
374     unlock_user_struct(frame, frame_addr, 1);
375     force_sigsegv(usig);
376 }
377 
378 static int
379 restore_sigcontext(CPUARMState *env, struct target_sigcontext *sc)
380 {
381     int err = 0;
382     uint32_t cpsr;
383 
384     __get_user(env->regs[0], &sc->arm_r0);
385     __get_user(env->regs[1], &sc->arm_r1);
386     __get_user(env->regs[2], &sc->arm_r2);
387     __get_user(env->regs[3], &sc->arm_r3);
388     __get_user(env->regs[4], &sc->arm_r4);
389     __get_user(env->regs[5], &sc->arm_r5);
390     __get_user(env->regs[6], &sc->arm_r6);
391     __get_user(env->regs[7], &sc->arm_r7);
392     __get_user(env->regs[8], &sc->arm_r8);
393     __get_user(env->regs[9], &sc->arm_r9);
394     __get_user(env->regs[10], &sc->arm_r10);
395     __get_user(env->regs[11], &sc->arm_fp);
396     __get_user(env->regs[12], &sc->arm_ip);
397     __get_user(env->regs[13], &sc->arm_sp);
398     __get_user(env->regs[14], &sc->arm_lr);
399     __get_user(env->regs[15], &sc->arm_pc);
400     __get_user(cpsr, &sc->arm_cpsr);
401     cpsr_write(env, cpsr, CPSR_USER | CPSR_EXEC, CPSRWriteByInstr);
402 
403     err |= !valid_user_regs(env);
404 
405     return err;
406 }
407 
408 static abi_ulong *restore_sigframe_vfp(CPUARMState *env, abi_ulong *regspace)
409 {
410     int i;
411     abi_ulong magic, sz;
412     uint32_t fpscr, fpexc;
413     struct target_vfp_sigframe *vfpframe;
414     vfpframe = (struct target_vfp_sigframe *)regspace;
415 
416     __get_user(magic, &vfpframe->magic);
417     __get_user(sz, &vfpframe->size);
418     if (magic != TARGET_VFP_MAGIC || sz != sizeof(*vfpframe)) {
419         return 0;
420     }
421     for (i = 0; i < 32; i++) {
422         __get_user(*aa32_vfp_dreg(env, i), &vfpframe->ufp.fpregs[i]);
423     }
424     __get_user(fpscr, &vfpframe->ufp.fpscr);
425     vfp_set_fpscr(env, fpscr);
426     __get_user(fpexc, &vfpframe->ufp_exc.fpexc);
427     /* Sanitise FPEXC: ensure VFP is enabled, FPINST2 is invalid
428      * and the exception flag is cleared
429      */
430     fpexc |= (1 << 30);
431     fpexc &= ~((1 << 31) | (1 << 28));
432     env->vfp.xregs[ARM_VFP_FPEXC] = fpexc;
433     __get_user(env->vfp.xregs[ARM_VFP_FPINST], &vfpframe->ufp_exc.fpinst);
434     __get_user(env->vfp.xregs[ARM_VFP_FPINST2], &vfpframe->ufp_exc.fpinst2);
435     return (abi_ulong*)(vfpframe + 1);
436 }
437 
438 static abi_ulong *restore_sigframe_iwmmxt(CPUARMState *env,
439                                           abi_ulong *regspace)
440 {
441     int i;
442     abi_ulong magic, sz;
443     struct target_iwmmxt_sigframe *iwmmxtframe;
444     iwmmxtframe = (struct target_iwmmxt_sigframe *)regspace;
445 
446     __get_user(magic, &iwmmxtframe->magic);
447     __get_user(sz, &iwmmxtframe->size);
448     if (magic != TARGET_IWMMXT_MAGIC || sz != sizeof(*iwmmxtframe)) {
449         return 0;
450     }
451     for (i = 0; i < 16; i++) {
452         __get_user(env->iwmmxt.regs[i], &iwmmxtframe->regs[i]);
453     }
454     __get_user(env->vfp.xregs[ARM_IWMMXT_wCSSF], &iwmmxtframe->wcssf);
455     __get_user(env->vfp.xregs[ARM_IWMMXT_wCASF], &iwmmxtframe->wcssf);
456     __get_user(env->vfp.xregs[ARM_IWMMXT_wCGR0], &iwmmxtframe->wcgr0);
457     __get_user(env->vfp.xregs[ARM_IWMMXT_wCGR1], &iwmmxtframe->wcgr1);
458     __get_user(env->vfp.xregs[ARM_IWMMXT_wCGR2], &iwmmxtframe->wcgr2);
459     __get_user(env->vfp.xregs[ARM_IWMMXT_wCGR3], &iwmmxtframe->wcgr3);
460     return (abi_ulong*)(iwmmxtframe + 1);
461 }
462 
463 static int do_sigframe_return(CPUARMState *env,
464                               target_ulong context_addr,
465                               struct target_ucontext *uc)
466 {
467     sigset_t host_set;
468     abi_ulong *regspace;
469 
470     target_to_host_sigset(&host_set, &uc->tuc_sigmask);
471     set_sigmask(&host_set);
472 
473     if (restore_sigcontext(env, &uc->tuc_mcontext)) {
474         return 1;
475     }
476 
477     /* Restore coprocessor signal frame */
478     regspace = uc->tuc_regspace;
479     if (cpu_isar_feature(aa32_vfp_simd, env_archcpu(env))) {
480         regspace = restore_sigframe_vfp(env, regspace);
481         if (!regspace) {
482             return 1;
483         }
484     }
485     if (arm_feature(env, ARM_FEATURE_IWMMXT)) {
486         regspace = restore_sigframe_iwmmxt(env, regspace);
487         if (!regspace) {
488             return 1;
489         }
490     }
491 
492     target_restore_altstack(&uc->tuc_stack, env);
493 
494 #if 0
495     /* Send SIGTRAP if we're single-stepping */
496     if (ptrace_cancel_bpt(current))
497         send_sig(SIGTRAP, current, 1);
498 #endif
499 
500     return 0;
501 }
502 
503 long do_sigreturn(CPUARMState *env)
504 {
505     abi_ulong frame_addr;
506     struct sigframe *frame = NULL;
507 
508     /*
509      * Since we stacked the signal on a 64-bit boundary,
510      * then 'sp' should be word aligned here.  If it's
511      * not, then the user is trying to mess with us.
512      */
513     frame_addr = env->regs[13];
514     trace_user_do_sigreturn(env, frame_addr);
515     if (frame_addr & 7) {
516         goto badframe;
517     }
518 
519     if (!lock_user_struct(VERIFY_READ, frame, frame_addr, 1)) {
520         goto badframe;
521     }
522 
523     if (do_sigframe_return(env,
524                            frame_addr + offsetof(struct sigframe, uc),
525                            &frame->uc)) {
526         goto badframe;
527     }
528 
529     unlock_user_struct(frame, frame_addr, 0);
530     return -QEMU_ESIGRETURN;
531 
532 badframe:
533     unlock_user_struct(frame, frame_addr, 0);
534     force_sig(TARGET_SIGSEGV);
535     return -QEMU_ESIGRETURN;
536 }
537 
538 long do_rt_sigreturn(CPUARMState *env)
539 {
540     abi_ulong frame_addr;
541     struct rt_sigframe *frame = NULL;
542 
543     /*
544      * Since we stacked the signal on a 64-bit boundary,
545      * then 'sp' should be word aligned here.  If it's
546      * not, then the user is trying to mess with us.
547      */
548     frame_addr = env->regs[13];
549     trace_user_do_rt_sigreturn(env, frame_addr);
550     if (frame_addr & 7) {
551         goto badframe;
552     }
553 
554     if (!lock_user_struct(VERIFY_READ, frame, frame_addr, 1)) {
555         goto badframe;
556     }
557 
558     if (do_sigframe_return(env,
559                            frame_addr + offsetof(struct rt_sigframe, sig.uc),
560                            &frame->sig.uc)) {
561         goto badframe;
562     }
563 
564     unlock_user_struct(frame, frame_addr, 0);
565     return -QEMU_ESIGRETURN;
566 
567 badframe:
568     unlock_user_struct(frame, frame_addr, 0);
569     force_sig(TARGET_SIGSEGV);
570     return -QEMU_ESIGRETURN;
571 }
572 
573 /*
574  * EABI syscalls pass the number via r7.
575  * Note that the kernel still adds the OABI syscall number to the trap,
576  * presumably for backward ABI compatibility with unwinders.
577  */
578 #define ARM_MOV_R7_IMM(X)       (0xe3a07000 | (X))
579 #define ARM_SWI_SYS(X)          (0xef000000 | (X) | ARM_SYSCALL_BASE)
580 
581 #define THUMB_MOVS_R7_IMM(X)    (0x2700 | (X))
582 #define THUMB_SWI_SYS           0xdf00
583 
584 static void write_arm_sigreturn(uint32_t *rc, int syscall)
585 {
586     __put_user(ARM_MOV_R7_IMM(syscall), rc);
587     __put_user(ARM_SWI_SYS(syscall), rc + 1);
588     /* Wrote 8 of 12 bytes */
589 }
590 
591 static void write_thm_sigreturn(uint32_t *rc, int syscall)
592 {
593     __put_user(THUMB_SWI_SYS << 16 | THUMB_MOVS_R7_IMM(syscall), rc);
594     /* Wrote 4 of 12 bytes */
595 }
596 
597 /*
598  * Stub needed to make sure the FD register (r9) contains the right value.
599  * Use the same instruction sequence as the kernel.
600  */
601 static void write_arm_fdpic_sigreturn(uint32_t *rc, int ofs)
602 {
603     assert(ofs <= 0xfff);
604     __put_user(0xe59d3000 | ofs, rc + 0);   /* ldr r3, [sp, #ofs] */
605     __put_user(0xe8930908, rc + 1);         /* ldm r3, { r3, r9 } */
606     __put_user(0xe12fff13, rc + 2);         /* bx  r3 */
607     /* Wrote 12 of 12 bytes */
608 }
609 
610 static void write_thm_fdpic_sigreturn(void *vrc, int ofs)
611 {
612     uint16_t *rc = vrc;
613 
614     assert((ofs & ~0x3fc) == 0);
615     __put_user(0x9b00 | (ofs >> 2), rc + 0);      /* ldr r3, [sp, #ofs] */
616     __put_user(0xcb0c, rc + 1);                   /* ldm r3, { r2, r3 } */
617     __put_user(0x4699, rc + 2);                   /* mov r9, r3 */
618     __put_user(0x4710, rc + 3);                   /* bx  r2 */
619     /* Wrote 8 of 12 bytes */
620 }
621 
622 void setup_sigtramp(abi_ulong sigtramp_page)
623 {
624     uint32_t total_size = 8 * RETCODE_BYTES;
625     uint32_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, total_size, 0);
626 
627     assert(tramp != NULL);
628 
629     default_sigreturn = sigtramp_page;
630     write_arm_sigreturn(&tramp[0 * RETCODE_WORDS], TARGET_NR_sigreturn);
631     write_thm_sigreturn(&tramp[1 * RETCODE_WORDS], TARGET_NR_sigreturn);
632     write_arm_sigreturn(&tramp[2 * RETCODE_WORDS], TARGET_NR_rt_sigreturn);
633     write_thm_sigreturn(&tramp[3 * RETCODE_WORDS], TARGET_NR_rt_sigreturn);
634 
635     sigreturn_fdpic_tramp = sigtramp_page + 4 * RETCODE_BYTES;
636     write_arm_fdpic_sigreturn(tramp + 4 * RETCODE_WORDS,
637                               offsetof(struct sigframe, retcode[3]));
638     write_thm_fdpic_sigreturn(tramp + 5 * RETCODE_WORDS,
639                                 offsetof(struct sigframe, retcode[3]));
640     write_arm_fdpic_sigreturn(tramp + 6 * RETCODE_WORDS,
641                               offsetof(struct rt_sigframe, sig.retcode[3]));
642     write_thm_fdpic_sigreturn(tramp + 7 * RETCODE_WORDS,
643                               offsetof(struct rt_sigframe, sig.retcode[3]));
644 
645     unlock_user(tramp, sigtramp_page, total_size);
646 }
647