Turning on ASSERT's in OTP code.

Paul Davis <>
Mon Jun 28 08:12:29 CEST 2010

I've stumbled across a weird segfault when sending terms from a thread
spawned by a NIF. Investigating this i followed a traceback to
erts/emulator/beam/erl_alloc_util.c. Glancing at the code in
erl_alloc_util.c I notice that the line before the crash is an assert.
Checking the value in gdb shows that the assertion is violated. My
first thought was to try and enable these asserts but I'm not sure
where to look for docs on how to do such a thing. Looking through the
code I see them looking for DEBUG to be defined yet nothing in
./configure's help suggests a flag to set.

In the interest of trying things I tried CFLAGS="-DDEBUG" ./configure
&& CFLAGS="-DDEBUG" make but it dies with an error about pcre.

Anyone have a pointer on where to look for getting these enabled?

Here's a copy of the traceback if it helps anyone. The lines in
erl_alloc_util.c starting at 598:

    crr->prev->next = crr->next;

gdb shows that crr is valid and crr->prev is NULL.

#0  0x08085e82 in unlink_carrier (allctr=0xa2dc140, blk=<value optimized out>)
    at beam/erl_alloc_util.c:599
#1  destroy_carrier (allctr=0xa2dc140, blk=<value optimized out>)
    at beam/erl_alloc_util.c:1615
#2  0x08087161 in do_erts_alcu_free (type=148, unused=0x8250b60, p=0xa2dd7f0)
    at beam/erl_alloc_util.c:2648
#3  erts_alcu_free_thr_pref (type=148, unused=0x8250b60, p=0xa2dd7f0)
    at beam/erl_alloc_util.c:2699
#4  0x081535da in erts_free (env=0xa2dd7f0) at beam/erl_alloc.h:210
#5  enif_free_env (env=0xa2dd7f0) at beam/erl_nif.c:256
#6  0x00e21218 in job_destroy (obj=0xa2dd7c0) at c_src/job.c:32
#7  0x00e21cda in queue_done (queue=0xa2dd718, item=0xa2dd7c0)
    at c_src/queue.c:184
#8  0x00e23849 in worker_exec (vm=0xa2a7d10) at c_src/worker.c:124
#9  0x00e2376d in worker_run (arg=0xa2dd628) at c_src/worker.c:85
#10 0x081d2a2c in thr_wrapper (vtwd=0xb64e5020) at common/ethread.c:480
#11 0x0068296e in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#12 0x00260a4e in clone () from /lib/tls/i686/cmov/libc.so.6

Paul Davis

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