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Asked: 2026-06-01T19:16:55+00:00

I found this in a multi-threaded c application. The authors commented that it’s used

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I found this in a multi-threaded c application. The authors commented that it’s used to make a thread crash in a custom assert function. GCC is fine with it, but clang issues the following warning:

note: consider using __builtin_trap() or qualifying pointer with 'volatile'

and also issues one of those, for each usage of the assert function:

warning: indirection of non-volatile null pointer will be deleted, not trap

What is going on here? Is __builtin_trap specific to clang? Should I use it?

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1 Answer

  1. Editorial Team

    Writing to NULL address is not guaranteed to crash your program reliably, so GCC introduced __builtin_trap for that.

    It looks like clang decided to go further, and eliminate such writes altogether, almost forcing you into using __builtin_trap. Their other option of casting NULL to volatile pointer does not look attractive compared to __builtin_trap, because it’s “merely” an undefined behavior.

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