Is there a way to print these in rust-lldb?

[vjpr]

I am using CLion with the Rust plugin.

Trying to debug a variable in the swc-project/swc project.

$ p src

(string_cache::atom::Atom<swc_atoms::JsWordStaticSet>) src = {
  unsafe_data = 140464742296960 {
    0 = 140464742296960
  }
  phantom = {}
}

[vjpr]

Work is ongoing here intellij-rust/intellij-rust#3000

[vjpr]

I actually will need help with this.

Is there a way to get the string from the unsafe_data ptr?

[vjpr]

This seems to work for me, but would be interested in input. I am new to Rust.

unsafe_data points to dynamic_set::Entry, which I then just read as a CString - which seems to work although I thought Rust's strs are not null-terminated.

This is using IntelliJ with the Rust plugin. Then you run a debug session.

---

~/.lldbinit

command script import ./summaries.py
command script import ./lldb_init.py

lldb_init.py

def __lldb_init_module(debugger, internal_dict):
  summary_cmd = (
    "type summary add "
    "Atom "
    "--expand "
    "--hide-empty "
    '--regex "string_cache::atom::Atom" '
    "--python-function summaries.AtomSummary "
    "--category Rust "
  )

  synthetic_cmd = (
      "type synthetic add "
      "Atom "
      "--python-class summaries.AtomProvider "
      '--regex "string_cache::atom::Atom" '
      "--category Rust "
    )


  # NOTE: If this command is incorrect `unknown option` is printed with no other debugging info.
  debugger.HandleCommand(summary_cmd)
  # debugger.HandleCommand(synthetic_cmd)

summaries.py

import lldb
import sys

PY3 = sys.version_info[0] == 3
if PY3:
  from typing import Optional

def AtomSummary(valobj, internal_dict):
  # type: (SBValue, dict) -> str

  process = valobj.GetProcess()

  # length = valobj.GetChildMemberWithName("length").GetValueAsUnsigned()
  length = 200
  if length == 0:
    return '""'

  unsafe_data = valobj.GetChildMemberWithName("unsafe_data")

  # From: https://github.com/servo/string-cache/blob/master/src/atom.rs
  TAG_MASK = 0b_11  # u8
  DYNAMIC_TAG = 0b_00  # u8
  INLINE_TAG = 0b_01  # b8 - len in upper nybble
  STATIC_TAG = 0b_10  # u8
  TAG_MASK = 0b_11
  LEN_OFFSET = 4
  LEN_MASK = 0xF0
  # ---

  # *const dynamic_set::Entry
  # https://docs.rs/string_cache/0.8.1/src/string_cache/dynamic_set.rs.html
  unsafe_data = unsafe_data.GetChildAtIndex(0).GetValueAsUnsigned()

  tag = unsafe_data & TAG_MASK  # u8

  type = 'unknown'
  if (tag == DYNAMIC_TAG): type = 'dynamic'
  if (tag == INLINE_TAG):  type = 'inline_tag'
  if (tag == STATIC_TAG): type = 'static_tag'

  if (unsafe_data == 0):
    return '""'

  # TODO(vjpr): Check tag to decide what to do.

  error = lldb.SBError()
  ptr_to_entry = process.ReadPointerFromMemory(unsafe_data, error)
  if error.Success():
    print('pointer: 0x%x' % ptr_to_entry)
  else:
    print('error: ', error)
    return '""'

  error = lldb.SBError()
  str = process.ReadCStringFromMemory(ptr_to_entry, length, error)

  print("ptr_to_entry: 0x{:x}, entry_ptr: 0x{:x}, tag: {}".format(unsafe_data, ptr_to_entry, tag))
  print("string: {}".format(str))

  return '"%s"' % str