Add functionality to find a task's stack buffer.

src/julia_gcext.h

@@ -114,4 +114,11 @@ JL_DLLEXPORT int jl_gc_conservative_gc_support_enabled(void);
 // jl_typeof(obj) is an actual type object.
 JL_DLLEXPORT jl_value_t *jl_gc_internal_obj_base_ptr(void *p);
 
+// Return a non-null pointer to the start of the stack area if the task
+// has an associated stack buffer. In that case, *size will also contain
+// the size of that stack buffer upon return. Also, if task is a thread's
+// current task, that thread's id will be stored in *tid; otherwise,
+// *tid will be set to -1.
+JL_DLLEXPORT void *jl_task_stack_buffer(jl_task_t *task, size_t *size, int *tid);
+
 #endif // _JULIA_GCEXT_H

src/task.c

@@ -57,6 +57,8 @@ volatile int jl_in_stackwalk = 0;
 #define MINSTKSZ 131072
 #endif
 
+#define ROOT_TASK_STACK_ADJUSTMENT 3000000
+
 static jl_sym_t *done_sym;
 static jl_sym_t *failed_sym;
 static jl_sym_t *runnable_sym;
@@ -179,6 +181,36 @@ static void JL_NORETURN finish_task(jl_task_t *t, jl_value_t *resultval JL_MAYBE
  abort();
 }
 
+JL_DLLEXPORT void *jl_task_stack_buffer(jl_task_t *task, size_t *size, int *tid)
+{
+ size_t off = 0;
+#ifndef _OS_WINDOWS_
+ if (jl_all_tls_states[0]->root_task == task) {
+ // See jl_init_root_task(). The root task of the main thread
+ // has its buffer enlarged by an artificial 3000000 bytes, but
+ // that means that the start of the buffer usually points to
+ // inaccessible memory. We need to correct for this.
+ off = ROOT_TASK_STACK_ADJUSTMENT;
+ }
+#endif
+ *tid = -1;
+ for (int i = 0; i < jl_n_threads; i++) {
+ jl_ptls_t ptls = jl_all_tls_states[i];
+ if (ptls->current_task == task) {
+ *tid = i;
+#ifdef COPY_STACKS
+ if (task->copy_stack) {
+ *size = ptls->stacksize;
+ return (char *)ptls->stackbase - *size;
+ }
+#endif
+ break; // continue with normal return
+ }
+ }
+ *size = task->bufsz - off;
+ return (void *)((char *)task->stkbuf + off);
+}
+
 static void record_backtrace(void) JL_NOTSAFEPOINT
 {
  jl_ptls_t ptls = jl_get_ptls_states();
@@ -813,8 +845,8 @@ void jl_init_root_task(void *stack_lo, void *stack_hi)
  size_t ssize = (char*)stack_hi - (char*)stack_lo;
 #ifndef _OS_WINDOWS_
  if (ptls->tid == 0) {
- stack = (void*)((char*)stack - 3000000); // offset our guess of the address of the bottom of stack to cover the guard pages too
- ssize += 3000000; // sizeof stack is known exactly, but not where we are in that stack
+ stack = (void*)((char*)stack - ROOT_TASK_STACK_ADJUSTMENT); // offset our guess of the address of the bottom of stack to cover the guard pages too
+ ssize += ROOT_TASK_STACK_ADJUSTMENT; // sizeof stack is known exactly, but not where we are in that stack
  }
 #endif
  ptls->current_task->stkbuf = stack;