libgo/runtime/stack.c

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Stack scanning code for the garbage collector.
   6
   7 #include "runtime.h"
   8
   9 #ifdef USING_SPLIT_STACK
  10
  11 extern void * __splitstack_find (void *, void *, size_t *, void **, void **,
  12                                  void **);
  13
  14 extern void * __splitstack_find_context (void *context[10], size_t *, void **,
  15                                          void **, void **);
  16
  17 #endif
  18
  19 bool runtime_usestackmaps;
  20
  21 // Calling unwind_init in doscanstack only works if it does not do a
  22 // tail call to doscanstack1.
  23 #pragma GCC optimize ("-fno-optimize-sibling-calls")
  24
  25 extern void scanstackblock(uintptr addr, uintptr size, void *gcw)
  26   __asm__("runtime.scanstackblock");
  27
  28 static bool doscanstack1(G*, void*)
  29   __attribute__ ((noinline));
  30
  31 // Scan gp's stack, passing stack chunks to scanstackblock.
  32 bool doscanstack(G *gp, void* gcw) {
  33         // Save registers on the stack, so that if we are scanning our
  34         // own stack we will see them.
  35         if (!runtime_usestackmaps) {
  36                 __builtin_unwind_init();
  37                 flush_registers_to_secondary_stack();
  38         }
  39
  40         return doscanstack1(gp, gcw);
  41 }
  42
  43 // Scan gp's stack after saving registers.
  44 static bool doscanstack1(G *gp, void *gcw) {
  45 #ifdef USING_SPLIT_STACK
  46         void* sp;
  47         size_t spsize;
  48         void* next_segment;
  49         void* next_sp;
  50         void* initial_sp;
  51         G* _g_;
  52
  53         _g_ = runtime_g();
  54         if (runtime_usestackmaps) {
  55                 // If stack map is enabled, we get here only when we can unwind
  56                 // the stack being scanned. That is, either we are scanning our
  57                 // own stack, or we are scanning through a signal handler.
  58                 __go_assert((_g_ == gp) || ((_g_ == gp->m->gsignal) && (gp == gp->m->curg)));
  59                 return scanstackwithmap(gcw);
  60         }
  61         if (_g_ == gp) {
  62                 // Scanning our own stack.
  63                 // If we are on a signal stack, it can unwind through the signal
  64                 // handler and see the g stack, so just scan our own stack.
  65                 sp = __splitstack_find(nil, nil, &spsize, &next_segment,
  66                                        &next_sp, &initial_sp);
  67         } else {
  68                 // Scanning another goroutine's stack.
  69                 // The goroutine is usually asleep (the world is stopped).
  70
  71                 // The exception is that if the goroutine is about to enter or might
  72                 // have just exited a system call, it may be executing code such
  73                 // as schedlock and may have needed to start a new stack segment.
  74                 // Use the stack segment and stack pointer at the time of
  75                 // the system call instead, since that won't change underfoot.
  76                 if(gp->gcstack != 0) {
  77                         sp = (void*)(gp->gcstack);
  78                         spsize = gp->gcstacksize;
  79                         next_segment = (void*)(gp->gcnextsegment);
  80                         next_sp = (void*)(gp->gcnextsp);
  81                         initial_sp = (void*)(gp->gcinitialsp);
  82                 } else {
  83                         sp = __splitstack_find_context((void**)(&gp->stackcontext[0]),
  84                                                        &spsize, &next_segment,
  85                                                        &next_sp, &initial_sp);
  86                 }
  87         }
  88         if(sp != nil) {
  89                 scanstackblock((uintptr)(sp), (uintptr)(spsize), gcw);
  90                 while((sp = __splitstack_find(next_segment, next_sp,
  91                                               &spsize, &next_segment,
  92                                               &next_sp, &initial_sp)) != nil)
  93                         scanstackblock((uintptr)(sp), (uintptr)(spsize), gcw);
  94         }
  95 #else
  96         byte* bottom;
  97         byte* top;
  98         byte* nextsp2;
  99         byte* initialsp2;
 100
 101         if(gp == runtime_g()) {
 102                 // Scanning our own stack.
 103                 bottom = (byte*)&gp;
 104                 nextsp2 = secondary_stack_pointer();
 105         } else {
 106                 // Scanning another goroutine's stack.
 107                 // The goroutine is usually asleep (the world is stopped).
 108                 bottom = (void*)gp->gcnextsp;
 109                 if(bottom == nil)
 110                         return true;
 111                 nextsp2 = (void*)gp->gcnextsp2;
 112         }
 113         top = (byte*)(void*)(gp->gcinitialsp) + gp->gcstacksize;
 114         if(top > bottom)
 115                 scanstackblock((uintptr)(bottom), (uintptr)(top - bottom), gcw);
 116         else
 117                 scanstackblock((uintptr)(top), (uintptr)(bottom - top), gcw);
 118         if (nextsp2 != nil) {
 119                 initialsp2 = (byte*)(void*)(gp->gcinitialsp2);
 120                 if(initialsp2 > nextsp2)
 121                         scanstackblock((uintptr)(nextsp2), (uintptr)(initialsp2 - nextsp2), gcw);
 122                 else
 123                         scanstackblock((uintptr)(initialsp2), (uintptr)(nextsp2 - initialsp2), gcw);
 124         }
 125 #endif
 126         return true;
 127 }