dotnet/runtime · error · RuntimeError

Couldn't determine list of JIT changes starting with…

Error message

Couldn't determine list of JIT changes starting with baseline hash

What it means

Raised by determine_base_jit when 'git log --pretty=format:%H <baseline_hash> -20 -- <jit paths>' returns nonzero. This command enumerates the last 20 commits starting at the baseline that touched the JIT sources (src/coreclr/jit/* and jiteeversionguid.h), to find candidate commits with a downloadable baseline JIT. A failure means git could not traverse the log, typically because the baseline_hash is invalid or unreachable.

Solutions

  1. Ensure baseline_hash is present: 'git -C <repo> cat-file -t <baseline_hash>' must report 'commit'.
  2. Deepen the clone: 'git fetch --unshallow origin' or increase --depth.
  3. Verify the src/coreclr/jit pathspec exists in the current checkout.
  4. Pass --base_git_hash <sha> explicitly with a commit you know is reachable.

Example fix

// before
command = ["git", "log", "--pretty=format:%H", baseline_hash, "-20", "--", "src/coreclr/jit/*", "src/coreclr/inc/jiteeversionguid.h"]
proc = subprocess.Popen(command, stdout=subprocess.PIPE)
stdout_change_list, _ = proc.communicate()
if proc.returncode != 0:
    raise RuntimeError("Couldn't determine list of JIT changes starting with baseline hash")
// after (fix invocation)
git -C <repo> cat-file -t <baseline_hash>   # must print 'commit'
git -C <repo> fetch --unshallow origin
python superpmi.py asmdiff --base_git_hash <known-good-sha> ...
Defensive patterns

Strategy: validation

Validate before calling

import subprocess
def validate_jit_change_list(repo_location, baseline_hash):
    cat = subprocess.run(['git', '-C', repo_location, 'cat-file', '-t', baseline_hash], capture_output=True)
    if cat.returncode != 0:
        raise RuntimeError(f"baseline_hash not present: {baseline_hash}; deepen the clone.")
    cmd = ['git', '-C', repo_location, 'log', '--pretty=format:%H', baseline_hash, '-20', '--', 'src/coreclr/jit/*', 'src/coreclr/inc/jiteeversionguid.h']
    proc = subprocess.run(cmd, capture_output=True)
    if proc.returncode != 0:
        raise RuntimeError(f"git log failed: {proc.stderr.decode('utf-8','replace').strip()}")
    return proc.stdout.decode('utf-8').strip().splitlines()

Prevention

When it happens

Trigger: subprocess.Popen(['git','log','--pretty=format:%H', baseline_hash, '-20','--','src/coreclr/jit/*','src/coreclr/inc/jiteeversionguid.h']) returns nonzero. Occurs when baseline_hash is unknown to the repo (shallow clone, missing object), when the pathspec matches nothing due to a relocated source tree, or when baseline_hash is malformed.

Common situations: Shallow or partial clone missing the baseline commit; running on an old checkout where src/coreclr layout differs; a baseline_hash computed from a fork that isn't present locally; corrupted object database.

Related errors

AI-assisted analysis of dotnet/runtime@60108ba66e (2026-08-10). Data as JSON: /api/errors/f027f78561161437. Report an issue: GitHub.

Appendix: source

Thrown at src/coreclr/scripts/superpmi.py:4910

                raise RuntimeError("Couldn't determine baseline git hash")

            baseline_hash = stdout_git_merge_base.decode('utf-8').strip()
            logging.info("Baseline hash: %s", baseline_hash)
        else:
            baseline_hash = coreclr_args.base_git_hash

        if coreclr_args.base_git_hash is None:
            # Enumerate the last 20 changes, starting with the baseline, that included JIT and JIT-EE GUID changes.
            command = [ "git", "log", "--pretty=format:%H", baseline_hash, "-20", "--", "src/coreclr/jit/*", "src/coreclr/inc/jiteeversionguid.h" ]
            logging.debug("Invoking: %s", " ".join(command))
            proc = subprocess.Popen(command, stdout=subprocess.PIPE)
            stdout_change_list, _ = proc.communicate()
            return_code = proc.returncode
            change_list_hashes = []
            if return_code == 0:
                change_list_hashes = stdout_change_list.decode('utf-8').strip().splitlines()
            else:
                raise RuntimeError("Couldn't determine list of JIT changes starting with baseline hash")

            if len(change_list_hashes) == 0:
                raise RuntimeError("No JIT changes found starting with baseline hash")
        else:
            # If `-base_git_hash` is specified, then we use exactly that hash and no other for the baseline.
            change_list_hashes = [ coreclr_args.base_git_hash ]

        # For each hash, (1) see if we have the JIT already, and if not (2) try to download the corresponding JIT from the rolling build.

        hashnum = 1
        for git_hash in change_list_hashes:
            logging.debug("%s: %s", hashnum, git_hash)

            jit_name = get_jit_name(coreclr_args)
            basejit_dir = os.path.join(default_basejit_root_dir, "{}.{}.{}.{}".format(git_hash, coreclr_args.host_os, coreclr_args.arch, coreclr_args.build_type))
            basejit_path = os.path.join(basejit_dir, jit_name)
            if os.path.isfile(basejit_path):
                # We found this baseline JIT in our cache; use it!

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