[Bug 227552] w, uptime i386 cordeump

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=227552

--- Comment #12 from Dimitry Andric <dim at FreeBSD.org> ---
I bisected, and it turns out r331838 (the merge of clang 6.0.0 and follow-up
fixes) is the first revision with those segfaults:

# ulimit -c 0; for i in /jail/test-r*; do echo "Using jail: $i"; chroot $i
/usr/bin/w; done
Using jail: /jail/test-r331837
12:00PM  up 13:47, 0 users, load averages: 0.23, 0.24, 0.60
USER       TTY      FROM                                      LOGIN@  IDLE WHAT
Using jail: /jail/test-r331838
Segmentation fault

Since all of the jail in r331837 has been compiled with clang 5.0.1, and all of
r331838 with clang 6.0.0, it is hard to say what is the exact cause.

Interestingly, moving around the libraries used by w seems to influence the
crash, at least for me.  So for example:

$ ldd /usr/bin/w
/usr/bin/w:
        libkvm.so.7 => /lib/libkvm.so.7 (0x28070000)
        libsbuf.so.6 => /lib/libsbuf.so.6 (0x2807d000)
        libxo.so.0 => /lib/libxo.so.0 (0x28080000)
        libutil.so.9 => /lib/libutil.so.9 (0x28099000)
        libc.so.7 => /lib/libc.so.7 (0x280ab000)
        libelf.so.2 => /lib/libelf.so.2 (0x2820a000)

$ /usr/bin/w
 2:05PM  up 13:53, 2 users, load averages: 2.31, 0.76, 0.66
USER       TTY      FROM                                      LOGIN@  IDLE WHAT
dim        pts/2    coleburn.home.andric.com                  2:02PM     - w

$ mkdir ~/foo

$ cp /lib/libkvm.so.7 /lib/libsbuf.so.6 /lib/libxo.so.0 /lib/libutil.so.9
/lib/libc.so.7 /lib/libelf.so.2 ~/foo

$ LD_LIBRARY_PATH=~/foo /usr/bin/w
Segmentation fault (core dumped)

Meaning, the exact same .so files, but in a different path, crash!  Currently,
I'm thinking that this may be something in the dynamic linker, but I'm still
not sure.

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