Add support for backtraces/info about active fibres

src/libfibre/libfibre.so-gdb.py

@@ -7,6 +7,7 @@ from contextlib import contextmanager
 class FibreSupport():
     def __init__(self):
         FibreSupport.list = []
+        FibreSupport.active = {}
         FibreSupport.saved = False
         if (gdb.lookup_symbol("_globalStackList")[0] == None):
             print()
@@ -28,9 +29,22 @@ class FibreSupport():
         while (next != first):
             FibreSupport.list.append(next)
             next = next['link'][1]['next']
+        orig_thread = gdb.selected_thread()
+        for thread in gdb.selected_inferior().threads():
+            thread.switch()
+            currStack = str(gdb.parse_and_eval("Context::currStack"))
+            # Cache the registers for this thread, in case it represents
+            # a fibre
+            FibreSupport.active[currStack] = {
+                    'rsp': str(gdb.parse_and_eval("$rsp")).split(None, 1)[0],
+                    'rbp': str(gdb.parse_and_eval("$rbp")).split(None, 1)[0],
+                    'rip': str(gdb.parse_and_eval("$rip")).split(None, 1)[0]
+            }
+        orig_thread.switch()
 
     def cont_handler(event):
         FibreSupport.list = []
+        FibreSupport.active = {}
 
     # ideally restore() would be hooked up with cont_handler,
     # but gdb currently fails with segmentation fault when trying
@@ -56,19 +70,28 @@ class FibreSupport():
         # if current pthread: use current register context
         if (arg == gdb.parse_and_eval("Context::currStack")):
             return True
-        # retrieve fibre's register context
-        ftype = gdb.lookup_type('Fibre').pointer()
-        ptr = gdb.Value(arg).cast(ftype)
-        rsp = ptr['stackPointer']
-        if (rsp == 0):
-            if not silent:
-                print("cannot access stack pointer - active in different thread?")
-            return False
-        ptype = gdb.lookup_type('uintptr_t').pointer()
-        rsp = rsp + 40            # cf. STACK_PUSH in src/generic/regsave.h
-        rbp = gdb.Value(rsp).cast(ptype).dereference()
-        rsp = rsp + 8
-        rip = gdb.Value(rsp).cast(ptype).dereference()
+        # Check active fibre cache in case this fibre is in it
+        # (FibreSupport.active is more up-to-date than
+        # StackContext for retrieving stack pointers)
+        argstr = str(arg)
+        if (argstr in FibreSupport.active):
+            rsp = FibreSupport.active[argstr]['rsp']
+            rbp = FibreSupport.active[argstr]['rbp']
+            rip = FibreSupport.active[argstr]['rip']
+        else:
+            # retrieve fibre's register context
+            ftype = gdb.lookup_type('Fibre').pointer()
+            ptr = gdb.Value(arg).cast(ftype)
+            rsp = ptr['stackPointer']
+            if (rsp == 0):
+                if not silent:
+                    print("cannot access stack pointer - active in different thread?")
+                return False
+            ptype = gdb.lookup_type('uintptr_t').pointer()
+            rsp = rsp + 40            # cf. STACK_PUSH in src/generic/regsave.h
+            rbp = gdb.Value(rsp).cast(ptype).dereference()
+            rsp = rsp + 8
+            rip = gdb.Value(rsp).cast(ptype).dereference()
         # enable fibre's register context
         gdb.execute("set $rsp = " + str(rsp))
         gdb.execute("set $rbp = " + str(rbp))