Tencent/matrix · error

Failed to create maps.txt

Error message

Failed to create maps.txt

What it means

SaveData() in unwind_for_offline writes the sorted /proc/<pid>/maps entries to 'maps.txt' with fopen("maps.txt","w+"). A null FILE* makes the tool print 'Failed to create maps.txt' (plus the errno detail from perror) and return false, so the offline unwind bundle cannot be produced. This is the first file the tool tries to create, so its failure usually blocks the whole capture.

Solutions

1. Start the tool from a writable directory (e.g. /data/local/tmp or $HOME)
2. Address the errno from perror: chmod/chown the directory or free disk space
3. Delete/rename any blocking maps.txt directory or file
4. Patch the tool to accept an output directory argument

Example fix

// before
fp(fopen("maps.txt", "w+"), &fclose);
// after
const char *out = getenv("UNWIND_OUT") ? getenv("UNWIND_OUT") : "maps.txt";
fp(fopen(out, "w+"), &fclose);

if (access(".", W_OK) != 0) { fprintf(stderr, "cwd not writable for maps.txt\n"); return 1; }

FILE *fp = fopen("maps.txt", "w+");
if (!fp) { perror("Failed to create maps.txt"); fp = fopen("/data/local/tmp/maps.txt", "w+"); }
if (!fp) return false;

When it happens

Trigger: fopen("maps.txt") fails in the tool's working directory: read-only filesystem, permission denied, disk full, or name collision with an existing directory; called from main after reading process maps.

Common situations: Running the tool in adb shell from /system or another unwritable path, SELinux denials on device, or CI containers with read-only workdirs while collecting maps for offline symbolication.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

• Failed to create file regs.txt
• Failed to create stack.data
• Matrix init, Matrix should not be null.
• you must init Matrix sdk first
• matrix init, application is null

AI-assisted analysis of Tencent/matrix@3b8293bd65 (2026-09-08). Data as JSON: /api/errors/da7cbd9ae9e8ffd1. Report an issue: GitHub.

Appendix: source

Thrown at matrix/matrix-android/matrix-backtrace/src/main/cpp/external/libunwindstack/tools/unwind_for_offline.cpp:311

    }
  }

  for (size_t i = 0; i < unwinder.NumFrames(); i++) {
    printf("%s\n", unwinder.FormatFrame(i).c_str());
  }

  if (!SaveStack(pid, stacks)) {
    return 1;
  }

  std::vector<std::pair<uint64_t, map_info_t>> sorted_maps(maps_by_start.begin(),
                                                           maps_by_start.end());
  std::sort(sorted_maps.begin(), sorted_maps.end(),
            [](auto& a, auto& b) { return a.first < b.first; });

  std::unique_ptr<FILE, decltype(&fclose)> fp(fopen("maps.txt", "w+"), &fclose);
  if (fp == nullptr) {
    perror("Failed to create maps.txt");
    return false;
  }

  for (auto& element : sorted_maps) {
    char perms[5] = {"---p"};
    map_info_t& map = element.second;
    if (map.flags & PROT_READ) {
      perms[0] = 'r';
    }
    if (map.flags & PROT_WRITE) {
      perms[1] = 'w';
    }
    if (map.flags & PROT_EXEC) {
      perms[2] = 'x';
    }
    fprintf(fp.get(), "%" PRIx64 "-%" PRIx64 " %s %" PRIx64 " 00:00 0", map.start, map.end, perms,
            map.offset);
    if (!map.name.empty()) {

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