Re: linux uml segfault

[Johannes Berg <johannes@sipsolutions.net>]

I think the problem is here:

> #24 0x000000006080f234 in ipc_init_ids (ids=0x60c60de8 <init_ipc_ns+8>)
> at ipc/util.c:119
> #25 0x0000000060813c6d in sem_init_ns (ns=0x60d895bb <textbuf+91>) at
> ipc/sem.c:254
> #26 0x0000000060015b5d in sem_init () at ipc/sem.c:268
> #27 0x00007f89906d92f7 in ?? () from /lib/x86_64-linux-
> gnu/libcom_err.so.2

You're in the init of libcom_err.so.2, which is loaded by

> "libnss_nis.so.2"

which is loaded by normal NSS code (getgrnam):

> #40 0x00007f89909bf3a6 in nss_load_library (ni=ni@entry=0x61497db0) at
> nsswitch.c:359
> #41 0x00007f89909bfc39 in __GI___nss_lookup_function (ni=0x61497db0,
> fct_name=<optimized out>, fct_name@entry=0x7f899089b020 "setgrent") at
> nsswitch.c:467
> #42 0x00007f899089554b in init_nss_interface () at nss_compat/compat-
> grp.c:83
> #43 init_nss_interface () at nss_compat/compat-grp.c:79
> #44 0x00007f8990895e35 in _nss_compat_getgrnam_r (name=0x7f8990a2a1e0
> "tty", grp=0x7ffe3e7a2910, buffer=0x7ffe3e7a24e0 "", buflen=1024,
> errnop=0x7f899089eb00) at nss_compat/compat-grp.c:486
> #45 0x00007f8990968b85 in __getgrnam_r (name=name@entry=0x7f8990a2a1e0
> "tty", resbuf=resbuf@entry=0x7ffe3e7a2910,
> buffer=buffer@entry=0x7ffe3e7a24e0 "", buflen=1024,
> result=result@entry=0x7ffe3e7a2908)
>     at ../nss/getXXbyYY_r.c:315


You have a strange nsswitch configuration that causes all of this
(libnss_nis.so.2 -> libcom_err.so.2) to get loaded.

Now libcom_err.so.2 is trying to call sem_init(), and that gets ... tada
... Linux's sem_init() instead of libpthread's.

And then the crash.

Now, I don't know how to fix it (short of changing your nsswitch
configuration) - maybe we could somehow rename sem_init()? Or maybe we
can somehow give the kernel binary a lower symbol resolution than the
libc/libpthread.


johannes


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