dotnet/runtime · error · RuntimeError

Error, toc file not created correctly at: %s

Error message

Error, toc file not created correctly at: %s

What it means

Raised in `__create_toc__` (superpmi.py:1462-1463) after running `mcs -toc <final.mch>`. The TOC file is `final_mch_file + '.mct'`; if it is not present after the command, the TOC generation failed. The TOC is required for indexed/random access into the MCH during replay.

Source

Thrown at src/coreclr/scripts/superpmi.py:1463

        if not self.coreclr_args.skip_cleanup:
            if os.path.isfile(self.base_mch_file):
                os.remove(self.base_mch_file)
                self.base_mch_file = None

    def __create_toc__(self):
        """ Create a TOC file

        Notes:
            <mcl> -toc <s_finalMchFile>
        """

        logging.info("Creating TOC file")

        command = [self.mcs_path, "-toc", self.final_mch_file]
        run_and_log(command)

        if not os.path.isfile(self.toc_file):
            raise RuntimeError("Error, toc file not created correctly at: %s" % self.toc_file)

    def __verify_final_mch__(self):
        """ Verify the resulting MCH file is error-free when running SuperPMI against it with the same JIT used for collection.

        Notes:
            <SuperPmiPath> -p -f <s_finalFailMclFile> <s_finalMchFile> <jitPath>
        """

        logging.info("Verifying MCH file")

        mch_files = [ self.final_mch_file ]
        spmi_replay = SuperPMIReplay(self.coreclr_args, mch_files, self.jit_path)
        passed = spmi_replay.replay()

        if not passed:
            raise RuntimeError("Error, unclean replay.")

    def __process_for_ci__(self):

View on GitHub (pinned to 290d5ab72c)

Solutions

1. Confirm final_mch_file is a valid non-empty MCH (errors 166/167 did not occur).
2. Inspect the logged `mcs -toc` output for the mcs return code/error.
3. Ensure the final MCH directory is writable and has disk space, then re-run with `--skip_collection_step --skip_merge_step`.

# Confirm the final MCH is valid before invoking the toc step
if not os.path.isfile(final_mch_file) or os.path.getsize(final_mch_file) == 0:
    raise SystemExit('final MCH missing/empty; cannot create TOC.')

try:
    collection.__create_toc__()
except RuntimeError as e:
    if 'toc file not created' in str(e):
        logging.error('mcs -toc failed; verify final MCH integrity and mcs output.')
    raise

When it happens

Trigger: The `mcs -toc` command ran but did not create the `.mct` file beside the final MCH. Causes: mcs error on a corrupt/empty final MCH, missing final MCH (errors 166/167), or a write/permission failure.

Common situations: final_mch_file is zero-length or corrupt from a bad merge/clean; mcs binary version mismatch; the MCH directory is read-only so the `.mct` cannot be written.

Related errors

• MCH file failed to be generated at: %s
• Final mch file failed to be generated.
• Error, unclean replay.
• No .mc files generated.
• No active session to reconnect

AI-assisted analysis of dotnet/runtime@290d5ab72c (2026-08-06). Data as JSON: /api/errors/7d16f3d867b152a2. Report an issue: GitHub.