How to force abort on "glibc detected *** free(): invalid pointer"

Question

In Linux environment, when getting "glibc detected *** free(): invalid pointer" errors, how do I identify which line of code is causing it?

Is there a way to force an abort? I recall there being an ENV var to control this?

How to set a breakpoint in gdb for the glibc error?

Answer 1

I believe if you setenv MALLOC_CHECK_ to 2, glibc will call abort() when it detects the "free(): invalid pointer" error. Note the trailing underscore in the name of the environment variable.

If MALLOC_CHECK_ is 1 glibc will print "free(): invalid pointer" (and similar printfs for other errors). If MALLOC_CHECK_ is 0, glibc will silently ignore such errors and simply return. If MALLOC_CHECK_ is 3 glibc will print the message and then call abort(). I.e. its a bitmask.

You can also call mallopt(M_CHECK_ACTION, arg) with an argument of 0-3, and get the same result as with MALLOC_CHECK_.

Since you're seeing the "free(): invalid pointer" message I think you must already be setting MALLOC_CHECK_ or calling mallopt(). By default glibc does not print those messages.

As for how to debug it, installing a handler for SIGABRT is probably the best way to proceed. You can set a breakpoint in your handler or deliberately trigger a core dump.

Answer 2

I recommend you get valgrind:

valgrind --tool=memcheck --leak-check=full ./a.out