LLDB script to visualise Odin slices, maps, and strings

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odin.py

import lldb

def is_slice_type(t, internal_dict):
    return t.name.startswith("[]") or t.name.startswith("[dynamic]")

class SliceChildProvider:
    def __init__(self, val, dict):
        self.val = val

    def num_children(self):
        return self.val.GetChildMemberWithName("len").GetValueAsSigned()

    def get_child_at_index(self, index):
        assert index >= 0 and index < self.num_children()

        data = self.val.GetChildMemberWithName("data")
        assert data.type.is_pointer
        first = data.deref

        offset = index * first.size
        return first.CreateChildAtOffset(f"[{index}]", offset, first.type)

def is_string_type(t, internal_dict):
    return t.name == "string"

def string_summary(value, internal_dict):
    pointer = value.GetChildMemberWithName("data").GetValueAsUnsigned(0)
    length = value.GetChildMemberWithName("len").GetValueAsSigned(0)
    if pointer == 0:
        return False
    if length == 0:
        return '""'
    error = lldb.SBError()
    string_data = value.process.ReadMemory(pointer, length, error)
    return '"{}"'.format(string_data.decode("utf-8"))

def is_map_type(t, internal_dict):
    return t.name.startswith("map[")

class MapChildProvider:

    def __init__(self, val, dict):
        self.val = val

    def num_children(self):
        return (self.val.GetChildMemberWithName("len").GetValueAsSigned() * 2) + 1

    def get_child_at_index(self, index):
        data = self.val.GetChildMemberWithName("data")
        tkey = data.GetChildMemberWithName("key").type
        tval = data.GetChildMemberWithName("value").type
        hash_field = data.GetChildMemberWithName("hash")
        key_cell   = data.GetChildMemberWithName("key_cell")
        value_cell = data.GetChildMemberWithName("value_cell")

        raw_data = data.GetValueAsUnsigned()
        key_ptr = raw_data & ~63
        cap_log2 = raw_data & 63
        cap = 0 if cap_log2 <= 0 else 1 << cap_log2

        key_cell_info = self.cell_info(tkey, key_cell)
        value_cell_info = self.cell_info(tval, value_cell)

        size_of_hash = hash_field.size
        assert size_of_hash == 8
    
        value_ptr = self.cell_index(key_ptr, key_cell_info, cap)
        hash_ptr =  self.cell_index(value_ptr, value_cell_info, cap)

        error = lldb.SBError()

        # Last one, the capacity.
        if index == self.num_children()-1:
            cap_data = lldb.SBData.CreateDataFromInt(cap)
            return self.val.CreateValueFromData("cap", cap_data, self.val.GetChildMemberWithName("len").type)

        wants_key = index % 2 == 0
        index = int(index / 2)

        key_index = 0
        for i in range(cap):
            TOMBSTONE_MASK = 1 << (size_of_hash*8 - 1)

            offset_hash = hash_ptr + i * size_of_hash

            hash_val = self.val.process.ReadUnsignedFromMemory(offset_hash, size_of_hash, error)
            if not error.success:
                print(error)
                continue
            elif hash_val == 0 or (hash_val & TOMBSTONE_MASK) != 0:
                continue

            offset_key   = self.cell_index(key_ptr, key_cell_info, i)
            offset_value = self.cell_index(value_ptr, value_cell_info, i)

            if index == key_index:
                if wants_key:
                    return self.val.CreateValueFromAddress(f"[{i}]", offset_key, tkey)
                else:
                    return self.val.CreateValueFromAddress(f"[{i}]", offset_value, tval)

            key_index += 1

        print("not found")

    def cell_info(self, typev, cell_type):
        elements_per_cell = 0

        if typev.size != cell_type.size:
            array_type = cell_type.children[0].type
            if array_type.size > 0 and typev.size > 0:
                elements_per_cell = array_type.size / typev.size

        if elements_per_cell == 0:
            elements_per_cell = 1

        return CellInfo(typev.size, cell_type.size, elements_per_cell)

    def cell_index(self, base, info, index):
        cell_index = 0
        data_index = 0
        if info.elements_per_cell == 1:
            return base + (index * info.size_of_cell)
        elif info.elements_per_cell == 2:
            cell_index = index >> 1;
            data_index = index & 1;
        elif info.elements_per_cell == 4:
            cell_index = index >> 2;
            data_index = index & 3;
        elif info.elements_per_cell == 8:
            cell_index = index >> 3;
            data_index = index & 7;
        elif info.elements_per_cell == 16:
            cell_index = index >> 4;
            data_index = index & 15;
        elif info.elements_per_cell == 32:
            cell_index = index >> 5;
            data_index = index & 31;
        else:
            cell_index = index / elements_per_cell;
            data_index = index % elements_per_cell;

        return base + (cell_index * info.size_of_cell) + (data_index * info.size_of_type);

class CellInfo:
    def __init__(self, size_of_type, size_of_cell, elements_per_cell):
        self.size_of_type = size_of_type
        self.size_of_cell = size_of_cell
        self.elements_per_cell = elements_per_cell

def __lldb_init_module(debugger, unused):
    debugger.HandleCommand(
        "type summary add --recognizer-function --python-function odin.string_summary odin.is_string_type"
    )
    debugger.HandleCommand(
        "type synth add --recognizer-function --python-class odin.SliceChildProvider odin.is_slice_type"
    )
    debugger.HandleCommand(
        "type synth add --recognizer-function --python-class odin.MapChildProvider odin.is_map_type"
    )

I have this automatically loaded in by adding the ~/.lldbinit file with the contents command script import ~/odin.py

Now, if you use the vscode extension for lldb, it will not load that automatically (vadimcn/codelldb#367) and you need to add a command to load it, if you look at the issue there are sample configurations.

Here's the slightly modified version to support chunked (sub-child ranges) output for large data sets: https://gist.github.com/harold-b/ef16a5c3ebcceccfc2bc7a5c5dd0058d

Very useful, although given the load command, it was required for me to put this script in a odin folder, because of the calls to odin.string_summary and so on. Otherwhise LLDB would not be able to find the definition.

Very useful, although given the load command, it was required for me to put this script in a odin folder, because of the calls to odin.string_summary and so on. Otherwhise LLDB would not be able to find the definition.

I think the file just has to be called odin for it to work, it determines the odin.is_map_type thing from that.