nodejs/node · error · Exception

Present value is %s

Error message

Present value is %s

What it means

Thrown by CustomMachineConfiguration.SetASLR in run_perf.py after writing a value to /proc/sys/kernel/randomize_va_space and reading it back: the read-back value differs from what was requested, so the kernel rejected or ignored the write. ASLR is pinned for benchmark reproducibility, so a mismatch aborts the run.

Source

Thrown at deps/v8/tools/run_perf.py:1089

      with open('/proc/sys/kernel/randomize_va_space', 'r') as f:
        return int(f.readline().strip())
    except Exception:
      logging.exception('Failed to get current ASLR settings.')
      raise

  @staticmethod
  def SetASLR(value):
    try:
      with open('/proc/sys/kernel/randomize_va_space', 'w') as f:
        f.write(str(value))
    except Exception:
      logging.exception(
          'Failed to update ASLR to %s. Are we running under sudo?', value)
      raise

    new_value = CustomMachineConfiguration.GetASLR()
    if value != new_value:
      raise Exception('Present value is %s' % new_value)

  @staticmethod
  def GetCPUCoresRange():
    try:
      with open('/sys/devices/system/cpu/present', 'r') as f:
        indexes = f.readline()
        r = list(map(int, indexes.split('-')))
        if len(r) == 1:
          return list(range(r[0], r[0] + 1))
        return list(range(r[0], r[1] + 1))
    except Exception:
      logging.exception('Failed to retrieve number of CPUs.')
      raise

  @staticmethod
  def GetCPUPathForId(cpu_index):
    ret = '/sys/devices/system/cpu/cpu'
    ret += str(cpu_index)

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Run the perf harness as root (sudo) so the write to /proc/sys/kernel/randomize_va_space takes effect.
2. If in a container, run with --privileged or mount /proc/sys read-write and confirm the host kernel allows the change.
3. Check for kernel lockdown / SELinux / AppArmor policies that block randomize_va_space writes and relax them for the benchmark host.
4. Manually verify with: sudo bash -c 'echo 0 > /proc/sys/kernel/randomize_va_space' then cat the file to confirm it stuck.

Example fix

# before
./run_perf.py --d8-path=out/Release/d8 suite.json
# after
sudo ./run_perf.py --d8-path=out/Release/d8 suite.json

import os
def can_set_aslr() -> bool:
    p = '/proc/sys/kernel/randomize_va_space'
    if not os.path.isfile(p):
        return False
    if os.access(p, os.W_OK):
        return True
    return os.geteuid() == 0  # will be writable once privileged

null

try:
    CustomMachineConfiguration.SetASLR(0)
except Exception as e:
    logging.warning('ASLR could not be pinned (%s); perf numbers may be noisy. Re-run with sudo / privileged container.', e)

When it happens

Trigger: SetASLR(value) is called (typically to disable ASLR for stable perf numbers); the write succeeds without exception but GetASLR() returns a different value. Common when not running as root (write silently fails or is buffered), when a security module (lockdown, GRKERNSEC) blocks the change, or inside a container/VM where /proc/sys is read-only.

Common situations: Running ./run_perf.py without sudo; running inside Docker/containerd where /proc/sys/kernel/randomize_va_space is mounted read-only or virtualized; kernel hardening that pins ASLR.

Related errors

• Could not set CPU governor. Present value is %s
• CPU cores have differing governor settings
• --v8-enable-hugepage is supported only on linux.
• %s only allows TraceConfig and LeafTraceConfig as child conf
• Invalid suite configuration.%s

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/3d8cd7dfafeac4b2. Report an issue: GitHub.