Solving a bug via lateral thinking
summary
A bug in Qt's V4 JavaScript engine makes a simple string comparison return true; GDB debugging fails because pointer tagging and optimizations defeat breakpoints, so an engineer builds minimal working and failing C++-API tests, instruments both with -pg and visualizes call traces with uftrace flamegraphs, locates a divergent branch, finds a broken overflow detection check, patches it, and verifies the bug is fixed in about two hours instead of weeks.
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