switchframe.c 3.9 KB

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  1. /*
  2. * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
  3. * The President and Fellows of Harvard College.
  4. *
  5. * Redistribution and use in source and binary forms, with or without
  6. * modification, are permitted provided that the following conditions
  7. * are met:
  8. * 1. Redistributions of source code must retain the above copyright
  9. * notice, this list of conditions and the following disclaimer.
  10. * 2. Redistributions in binary form must reproduce the above copyright
  11. * notice, this list of conditions and the following disclaimer in the
  12. * documentation and/or other materials provided with the distribution.
  13. * 3. Neither the name of the University nor the names of its contributors
  14. * may be used to endorse or promote products derived from this software
  15. * without specific prior written permission.
  16. *
  17. * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
  18. * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19. * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20. * ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
  21. * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22. * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23. * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24. * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25. * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26. * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27. * SUCH DAMAGE.
  28. */
  29. #include <types.h>
  30. #include <lib.h>
  31. #include <thread.h>
  32. #include <threadprivate.h>
  33. #include "switchframe.h"
  34. /* in threadstart.S */
  35. extern void mips_threadstart(/* arguments are in unusual registers */);
  36. /*
  37. * Function to initialize the switchframe of a new thread, which is
  38. * *not* the one that is currently running.
  39. *
  40. * The new thread should, when it is run the first time, end up calling
  41. * thread_startup(entrypoint, data1, data2).
  42. *
  43. * We arrange for this by creating a phony switchframe for
  44. * switchframe_switch() to switch to. The only trouble is that the
  45. * switchframe doesn't include the argument registers a0-a3. So we
  46. * store the arguments in the s* registers, and use a bit of asm
  47. * (mips_threadstart) to move them and then jump to thread_startup.
  48. */
  49. void
  50. switchframe_init(struct thread *thread,
  51. void (*entrypoint)(void *data1, unsigned long data2),
  52. void *data1, unsigned long data2)
  53. {
  54. vaddr_t stacktop;
  55. struct switchframe *sf;
  56. /*
  57. * MIPS stacks grow down. t_stack is just a hunk of memory, so
  58. * get the other end of it. Then set up a switchframe on the
  59. * top of the stack.
  60. */
  61. stacktop = ((vaddr_t)thread->t_stack) + STACK_SIZE;
  62. sf = ((struct switchframe *) stacktop) - 1;
  63. /* Zero out the switchframe. */
  64. bzero(sf, sizeof(*sf));
  65. /*
  66. * Now set the important parts: pass through the three arguments,
  67. * and set the return address register to the place we want
  68. * execution to begin.
  69. *
  70. * Thus, when switchframe_switch does its "j ra", it will
  71. * actually jump to mips_threadstart, which will move the
  72. * arguments into the right register and jump to
  73. * thread_startup().
  74. *
  75. * Note that this means that when we call switchframe_switch()
  76. * in thread_switch(), we may not come back out the same way
  77. * in the next thread. (Though we will come back out the same
  78. * way when we later come back to the same thread again.)
  79. *
  80. * This has implications for code at the bottom of
  81. * thread_switch, described in thread.c.
  82. */
  83. sf->sf_s0 = (uint32_t)entrypoint;
  84. sf->sf_s1 = (uint32_t)data1;
  85. sf->sf_s2 = (uint32_t)data2;
  86. sf->sf_ra = (uint32_t)mips_threadstart;
  87. /* Set ->t_context, and we're done. */
  88. thread->t_context = sf;
  89. }