Segmentation Fault in replacePlaceholders() with Datadog Integration cue to Fiber corruption caused by variable reuse

Problem/Motivation

When rendering placeholders in replacePlaceholders() within Drupal 10.3x, a segmentation fault can occur due to improper handling of PHP Fibers. The issue arises because the $placeholder variable from the initial foreach loop is reused in the subsequent foreach loop in the following while loop. This leads to corruption of the Fibers, as they may access inconsistent or overwritten state during execution.

The segmentation fault occurs because Fibers rely on strict state management, and reusing the $placeholder variable introduces unintended side effects that compromise Fiber integrity.

Steps to reproduce

• Make sure Datadog Tracer is installed and enabled on your environment
• Set up a Drupal 10.3.10 site with a theme or module that uses lazy builders for placeholders (e.g., for rendering status messages or other dynamic content).
• Ensure the replacePlaceholders() method is invoked on a renderable array containing multiple placeholders.
• Observe that under certain circumstances (e.g., heavy traffic or complex placeholder rendering), the application crashes with a segmentation fault.

Proposed resolution

The issue can be resolved by using distinct variable names for the foreach loop and the while loop to avoid unintended overwrites of the $placeholder variable. Specifically:

• In the foreach loop, keep $placeholder as it is.
• In the foreach loop inside the while loop, introduce a separate variable, such as $fiber_placeholder, to manage Fiber processing.

Remaining tasks

• Verify that the proposed resolution resolves the segmentation fault issue.
• Add test cases to ensure that placeholders render correctly without errors or segmentation faults.
• Review and merge the fix into the appropriate Drupal core branch.

User interface changes

none

Introduced terminology

none

API changes

none

Data model changes

none

Release notes snippet

Fixed a segmentation fault issue in replacePlaceholders() caused by the reuse of the $placeholder variable across multiple loops. This issue was addressed by using distinct variable names to prevent Fiber corruption during placeholder rendering.