arch/x86/include/asm/switch_to.h

   1 #ifndef _ASM_X86_SWITCH_TO_H
   2 #define _ASM_X86_SWITCH_TO_H
   3
   4 struct task_struct; /* one of the stranger aspects of C forward declarations */
   5 __visible struct task_struct *__switch_to(struct task_struct *prev,
   6                                            struct task_struct *next);
   7 struct tss_struct;
   8 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
   9                       struct tss_struct *tss);
  10
  11 #ifdef CONFIG_X86_32
  12
  13 #ifdef CONFIG_CC_STACKPROTECTOR
  14 #define __switch_canary                                                 \
  15         "movl %P[task_canary](%[next]), %%ebx\n\t"                      \
  16         "movl %%ebx, "__percpu_arg([stack_canary])"\n\t"
  17 #define __switch_canary_oparam                                          \
  18         , [stack_canary] "=m" (stack_canary.canary)
  19 #define __switch_canary_iparam                                          \
  20         , [task_canary] "i" (offsetof(struct task_struct, stack_canary))
  21 #else   /* CC_STACKPROTECTOR */
  22 #define __switch_canary
  23 #define __switch_canary_oparam
  24 #define __switch_canary_iparam
  25 #endif  /* CC_STACKPROTECTOR */
  26
  27 /*
  28  * Saving eflags is important. It switches not only IOPL between tasks,
  29  * it also protects other tasks from NT leaking through sysenter etc.
  30  */
  31 #define switch_to(prev, next, last)                                     \
  32 do {                                                                    \
  33         /*                                                              \
  34          * Context-switching clobbers all registers, so we clobber      \
  35          * them explicitly, via unused output variables.                \
  36          * (EAX and EBP is not listed because EBP is saved/restored     \
  37          * explicitly for wchan access and EAX is the return value of   \
  38          * __switch_to())                                               \
  39          */                                                             \
  40         unsigned long ebx, ecx, edx, esi, edi;                          \
  41                                                                         \
  42         asm volatile("pushl %%ebp\n\t"          /* save    EBP   */     \
  43                      "movl %%esp,%[prev_sp]\n\t"        /* save    ESP   */ \
  44                      "movl %[next_sp],%%esp\n\t"        /* restore ESP   */ \
  45                      "movl $1f,%[prev_ip]\n\t"  /* save    EIP   */     \
  46                      "pushl %[next_ip]\n\t"     /* restore EIP   */     \
  47                      __switch_canary                                    \
  48                      "jmp __switch_to\n"        /* regparm call  */     \
  49                      "1:\t"                                             \
  50                      "popl %%ebp\n\t"           /* restore EBP   */     \
  51                                                                         \
  52                      /* output parameters */                            \
  53                      : [prev_sp] "=m" (prev->thread.sp),                \
  54                        [prev_ip] "=m" (prev->thread.ip),                \
  55                        "=a" (last),                                     \
  56                                                                         \
  57                        /* clobbered output registers: */                \
  58                        "=b" (ebx), "=c" (ecx), "=d" (edx),              \
  59                        "=S" (esi), "=D" (edi)                           \
  60                                                                         \
  61                        __switch_canary_oparam                           \
  62                                                                         \
  63                        /* input parameters: */                          \
  64                      : [next_sp]  "m" (next->thread.sp),                \
  65                        [next_ip]  "m" (next->thread.ip),                \
  66                                                                         \
  67                        /* regparm parameters for __switch_to(): */      \
  68                        [prev]     "a" (prev),                           \
  69                        [next]     "d" (next)                            \
  70                                                                         \
  71                        __switch_canary_iparam                           \
  72                                                                         \
  73                      : /* reloaded segment registers */                 \
  74                         "memory");                                      \
  75 } while (0)
  76
  77 #else /* CONFIG_X86_32 */
  78
  79 /* frame pointer must be last for get_wchan */
  80 #define SAVE_CONTEXT    "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
  81 #define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
  82
  83 #define __EXTRA_CLOBBER  \
  84         , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
  85           "r12", "r13", "r14", "r15", "flags"
  86
  87 #ifdef CONFIG_CC_STACKPROTECTOR
  88 #define __switch_canary                                                   \
  89         "movq %P[task_canary](%%rsi),%%r8\n\t"                            \
  90         "movq %%r8,"__percpu_arg([gs_canary])"\n\t"
  91 #define __switch_canary_oparam                                            \
  92         , [gs_canary] "=m" (irq_stack_union.stack_canary)
  93 #define __switch_canary_iparam                                            \
  94         , [task_canary] "i" (offsetof(struct task_struct, stack_canary))
  95 #else   /* CC_STACKPROTECTOR */
  96 #define __switch_canary
  97 #define __switch_canary_oparam
  98 #define __switch_canary_iparam
  99 #endif  /* CC_STACKPROTECTOR */
 100
 101 /*
 102  * There is no need to save or restore flags, because flags are always
 103  * clean in kernel mode, with the possible exception of IOPL.  Kernel IOPL
 104  * has no effect.
 105  */
 106 #define switch_to(prev, next, last) \
 107         asm volatile(SAVE_CONTEXT                                         \
 108              "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */       \
 109              "movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */    \
 110              "call __switch_to\n\t"                                       \
 111              "movq "__percpu_arg([current_task])",%%rsi\n\t"              \
 112              __switch_canary                                              \
 113              "movq %P[thread_info](%%rsi),%%r8\n\t"                       \
 114              "movq %%rax,%%rdi\n\t"                                       \
 115              "testl  %[_tif_fork],%P[ti_flags](%%r8)\n\t"                 \
 116              "jnz   ret_from_fork\n\t"                                    \
 117              RESTORE_CONTEXT                                              \
 118              : "=a" (last)                                                \
 119                __switch_canary_oparam                                     \
 120              : [next] "S" (next), [prev] "D" (prev),                      \
 121                [threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
 122                [ti_flags] "i" (offsetof(struct thread_info, flags)),      \
 123                [_tif_fork] "i" (_TIF_FORK),                               \
 124                [thread_info] "i" (offsetof(struct task_struct, stack)),   \
 125                [current_task] "m" (current_task)                          \
 126                __switch_canary_iparam                                     \
 127              : "memory", "cc" __EXTRA_CLOBBER)
 128
 129 #endif /* CONFIG_X86_32 */
 130
 131 #endif /* _ASM_X86_SWITCH_TO_H */