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 // Calling unwind_init in doscanstack only works if it does not do a
  20 // tail call to doscanstack1.
  21 #pragma GCC optimize ("-fno-optimize-sibling-calls")
  22
  23 extern void scanstackblock(void *addr, uintptr size, void *gcw)
  24   __asm__("runtime.scanstackblock");
  25
  26 void doscanstack(G*, void*)
  27   __asm__("runtime.doscanstack");
  28
  29 static void doscanstack1(G*, void*)
  30   __attribute__ ((noinline));
  31
  32 // Scan gp's stack, passing stack chunks to scanstackblock.
  33 void doscanstack(G *gp, void* gcw) {
  34         // Save registers on the stack, so that if we are scanning our
  35         // own stack we will see them.
  36         __builtin_unwind_init();
  37
  38         doscanstack1(gp, gcw);
  39 }
  40
  41 // Scan gp's stack after saving registers.
  42 static void doscanstack1(G *gp, void *gcw) {
  43 #ifdef USING_SPLIT_STACK
  44         void* sp;
  45         size_t spsize;
  46         void* next_segment;
  47         void* next_sp;
  48         void* initial_sp;
  49
  50         if (gp == runtime_g()) {
  51                 // Scanning our own stack.
  52                 sp = __splitstack_find(nil, nil, &spsize, &next_segment,
  53                                        &next_sp, &initial_sp);
  54         } else {
  55                 // Scanning another goroutine's stack.
  56                 // The goroutine is usually asleep (the world is stopped).
  57
  58                 // The exception is that if the goroutine is about to enter or might
  59                 // have just exited a system call, it may be executing code such
  60                 // as schedlock and may have needed to start a new stack segment.
  61                 // Use the stack segment and stack pointer at the time of
  62                 // the system call instead, since that won't change underfoot.
  63                 if(gp->gcstack != 0) {
  64                         sp = (void*)(gp->gcstack);
  65                         spsize = gp->gcstacksize;
  66                         next_segment = (void*)(gp->gcnextsegment);
  67                         next_sp = (void*)(gp->gcnextsp);
  68                         initial_sp = (void*)(gp->gcinitialsp);
  69                 } else {
  70                         sp = __splitstack_find_context((void**)(&gp->stackcontext[0]),
  71                                                        &spsize, &next_segment,
  72                                                        &next_sp, &initial_sp);
  73                 }
  74         }
  75         if(sp != nil) {
  76                 scanstackblock(sp, (uintptr)(spsize), gcw);
  77                 while((sp = __splitstack_find(next_segment, next_sp,
  78                                               &spsize, &next_segment,
  79                                               &next_sp, &initial_sp)) != nil)
  80                         scanstackblock(sp, (uintptr)(spsize), gcw);
  81         }
  82 #else
  83         byte* bottom;
  84         byte* top;
  85
  86         if(gp == runtime_g()) {
  87                 // Scanning our own stack.
  88                 bottom = (byte*)&gp;
  89         } else {
  90                 // Scanning another goroutine's stack.
  91                 // The goroutine is usually asleep (the world is stopped).
  92                 bottom = (void*)gp->gcnextsp;
  93                 if(bottom == nil)
  94                         return;
  95         }
  96         top = (byte*)(void*)(gp->gcinitialsp) + gp->gcstacksize;
  97         if(top > bottom)
  98                 scanstackblock(bottom, (uintptr)(top - bottom), gcw);
  99         else
 100                 scanstackblock(top, (uintptr)(bottom - top), gcw);
 101 #endif
 102 }