Add a gdb helper for jit backtraces

Author: bjorn3

scripts/jit-helpers.py

@@ -0,0 +1,52 @@
+import gdb
+
+def jitmap_raw():
+    pid = gdb.selected_inferior().pid
+    jitmap_file = open("/tmp/perf-%d.map" % (pid,), "r")
+    jitmap = jitmap_file.read()
+    jitmap_file.close()
+    return jitmap
+
+def jit_functions():
+    jitmap = jitmap_raw()
+
+    functions = []
+    for line in jitmap.strip().split("\n"):
+        [addr, size, name] = line.split(" ")
+        functions.append((int(addr, 16), int(size, 16), name))
+
+    return functions
+
+class JitDecorator(gdb.FrameDecorator.FrameDecorator):
+    def __init__(self, fobj, name):
+        super(JitDecorator, self).__init__(fobj)
+        self.name = name
+
+    def function(self):
+        return self.name
+
+class JitFilter:
+    """
+    A backtrace filter which reads perf map files produced by cranelift-jit.
+    """
+
+    def __init__(self):
+        self.name = 'JitFilter'
+        self.enabled = True
+        self.priority = 0
+
+        gdb.current_progspace().frame_filters[self.name] = self
+
+    # FIXME add an actual unwinder or somehow register JITed .eh_frame with gdb to avoid relying on
+    # gdb unwinder heuristics.
+    def filter(self, frame_iter):
+        for frame in frame_iter:
+            frame_addr = frame.inferior_frame().pc()
+            for (addr, size, name) in jit_functions():
+                if frame_addr >= addr and frame_addr < addr + size:
+                    yield JitDecorator(frame, name)
+                    break
+            else:
+                yield frame
+
+JitFilter()