Linux Kernel  3.7.1
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process.c
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1 /*
2  * Process creation support for Hexagon
3  *
4  * Copyright (c) 2010-2012, The Linux Foundation. All rights reserved.
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 version 2 and
8  * only version 2 as published by the Free Software Foundation.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
18  * 02110-1301, USA.
19  */
20 
21 #include <linux/sched.h>
22 #include <linux/types.h>
23 #include <linux/module.h>
24 #include <linux/tick.h>
25 #include <linux/uaccess.h>
26 #include <linux/slab.h>
27 
28 /*
29  * Kernel thread creation. The desired kernel function is "wrapped"
30  * in the kernel_thread_helper function, which does cleanup
31  * afterwards.
32  */
33 static void __noreturn kernel_thread_helper(void *arg, int (*fn)(void *))
34 {
35  do_exit(fn(arg));
36 }
37 
38 int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
39 {
40  struct pt_regs regs;
41 
42  memset(&regs, 0, sizeof(regs));
43  /*
44  * Yes, we're exploting illicit knowledge of the ABI here.
45  */
46  regs.r00 = (unsigned long) arg;
47  regs.r01 = (unsigned long) fn;
48  pt_set_elr(&regs, (unsigned long)kernel_thread_helper);
49  pt_set_kmode(&regs);
50 
51  return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
52 }
54 
55 /*
56  * Program thread launch. Often defined as a macro in processor.h,
57  * but we're shooting for a small footprint and it's not an inner-loop
58  * performance-critical operation.
59  *
60  * The Hexagon ABI specifies that R28 is zero'ed before program launch,
61  * so that gets automatically done here. If we ever stop doing that here,
62  * we'll probably want to define the ELF_PLAT_INIT macro.
63  */
64 void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
65 {
66  /* Set to run with user-mode data segmentation */
67  set_fs(USER_DS);
68  /* We want to zero all data-containing registers. Is this overkill? */
69  memset(regs, 0, sizeof(*regs));
70  /* We might want to also zero all Processor registers here */
71  pt_set_usermode(regs);
72  pt_set_elr(regs, pc);
73  pt_set_rte_sp(regs, sp);
74 }
75 
76 /*
77  * Spin, or better still, do a hardware or VM wait instruction
78  * If hardware or VM offer wait termination even though interrupts
79  * are disabled.
80  */
81 static void default_idle(void)
82 {
83  __vmwait();
84 }
85 
86 void (*idle_sleep)(void) = default_idle;
87 
88 void cpu_idle(void)
89 {
90  while (1) {
91  tick_nohz_idle_enter();
93  while (!need_resched()) {
94  idle_sleep();
95  /* interrupts wake us up, but aren't serviced */
96  local_irq_enable(); /* service interrupt */
98  }
100  tick_nohz_idle_exit();
101  schedule();
102  }
103 }
104 
105 /*
106  * Return saved PC of a blocked thread
107  */
108 unsigned long thread_saved_pc(struct task_struct *tsk)
109 {
110  return 0;
111 }
112 
113 /*
114  * Copy architecture-specific thread state
115  */
116 int copy_thread(unsigned long clone_flags, unsigned long usp,
117  unsigned long unused, struct task_struct *p,
118  struct pt_regs *regs)
119 {
120  struct thread_info *ti = task_thread_info(p);
121  struct hexagon_switch_stack *ss;
122  struct pt_regs *childregs;
123  asmlinkage void ret_from_fork(void);
124 
125  childregs = (struct pt_regs *) (((unsigned long) ti + THREAD_SIZE) -
126  sizeof(*childregs));
127 
128  memcpy(childregs, regs, sizeof(*childregs));
129  ti->regs = childregs;
130 
131  /*
132  * Establish kernel stack pointer and initial PC for new thread
133  */
134  ss = (struct hexagon_switch_stack *) ((unsigned long) childregs -
135  sizeof(*ss));
136  ss->lr = (unsigned long)ret_from_fork;
137  p->thread.switch_sp = ss;
138 
139  /* If User mode thread, set pt_reg stack pointer as per parameter */
140  if (user_mode(childregs)) {
141  pt_set_rte_sp(childregs, usp);
142 
143  /* Child sees zero return value */
144  childregs->r00 = 0;
145 
146  /*
147  * The clone syscall has the C signature:
148  * int [r0] clone(int flags [r0],
149  * void *child_frame [r1],
150  * void *parent_tid [r2],
151  * void *child_tid [r3],
152  * void *thread_control_block [r4]);
153  * ugp is used to provide TLS support.
154  */
155  if (clone_flags & CLONE_SETTLS)
156  childregs->ugp = childregs->r04;
157 
158  /*
159  * Parent sees new pid -- not necessary, not even possible at
160  * this point in the fork process
161  * Might also want to set things like ti->addr_limit
162  */
163  } else {
164  /*
165  * If kernel thread, resume stack is kernel stack base.
166  * Note that this is pointer arithmetic on pt_regs *
167  */
168  pt_set_rte_sp(childregs, (unsigned long)(childregs + 1));
169  /*
170  * We need the current thread_info fast path pointer
171  * set up in pt_regs. The register to be used is
172  * parametric for assembler code, but the mechanism
173  * doesn't drop neatly into C. Needs to be fixed.
174  */
175  childregs->THREADINFO_REG = (unsigned long) ti;
176  }
177 
178  /*
179  * thread_info pointer is pulled out of task_struct "stack"
180  * field on switch_to.
181  */
182  p->stack = (void *)ti;
183 
184  return 0;
185 }
186 
187 /*
188  * Release any architecture-specific resources locked by thread
189  */
190 void release_thread(struct task_struct *dead_task)
191 {
192 }
193 
194 /*
195  * Free any architecture-specific thread data structures, etc.
196  */
197 void exit_thread(void)
198 {
199 }
200 
201 /*
202  * Some archs flush debug and FPU info here
203  */
204 void flush_thread(void)
205 {
206 }
207 
208 /*
209  * The "wait channel" terminology is archaic, but what we want
210  * is an identification of the point at which the scheduler
211  * was invoked by a blocked thread.
212  */
213 unsigned long get_wchan(struct task_struct *p)
214 {
215  unsigned long fp, pc;
216  unsigned long stack_page;
217  int count = 0;
218  if (!p || p == current || p->state == TASK_RUNNING)
219  return 0;
220 
221  stack_page = (unsigned long)task_stack_page(p);
222  fp = ((struct hexagon_switch_stack *)p->thread.switch_sp)->fp;
223  do {
224  if (fp < (stack_page + sizeof(struct thread_info)) ||
225  fp >= (THREAD_SIZE - 8 + stack_page))
226  return 0;
227  pc = ((unsigned long *)fp)[1];
228  if (!in_sched_functions(pc))
229  return pc;
230  fp = *(unsigned long *) fp;
231  } while (count++ < 16);
232 
233  return 0;
234 }
235 
236 /*
237  * Required placeholder.
238  */
240 {
241  return 0;
242 }