Avoiding sysctl at program startup using ELF aux vector (was: concurrent sysctl implementation)

Kostik Belousov kostikbel at gmail.com
Sat Aug 14 14:35:05 UTC 2010 

On Sat, Aug 07, 2010 at 09:37:22PM +0200, Marius Strobl wrote:
> On Sat, Aug 07, 2010 at 09:09:04PM +0300, Kostik Belousov wrote:
> > On Sat, Aug 07, 2010 at 03:59:39PM +0200, Marius Strobl wrote:
> > > On Fri, Aug 06, 2010 at 02:11:31PM +0300, Kostik Belousov wrote:
> > > > On Fri, Aug 06, 2010 at 01:08:08PM +0200, Marius Strobl wrote:
> > > > > On Fri, Aug 06, 2010 at 12:04:04PM +0300, Kostik Belousov wrote:
> > > > > > On Fri, Aug 06, 2010 at 07:06:33AM +0200, Jeremie Le Hen wrote:
> > > > > > > Hi Kib,
> > > > > > > 
> > > > > > > In-Reply-To: <20100629083901.GG13238 at deviant.kiev.zoral.com.ua>
> > > > > > > On Tue, Jun 29, 2010 at 11:39:01AM +0300, Kostik Belousov wrote:
> > > > > > > > On Tue, Jun 29, 2010 at 10:26:39AM +0200, Marius Strobl wrote:
> > > > > > > > > On Mon, Jun 28, 2010 at 05:48:59PM +0300, Kostik Belousov wrote:
> > > > > > > > > > On Wed, Jun 23, 2010 at 11:09:59PM +0200, Jeremie Le Hen wrote:
> > > > > > > > > > > Hi Kostik,
> > > > > > > > > > > 
> > > > > > > > > > > This patch seems to have faded out from memory.  Is it possible to go
> > > > > > > > > > > forward and commit it?
> > > > > > > > > > I refreshed the patch. Hopefully, nobody will object, and I commit it
> > > > > > > > > > shortly.
> > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > Thanks,
> > > > > > > > > > > Regards.
> > > > > > > > > > > 
> > > > > > > > > > > On Sat, Jul 25, 2009 at 12:29:16AM +0300, Kostik Belousov wrote:
> > > > > > > > > > > > Below is the prototype that seems to work for me both with patched and
> > > > > > > > > > > > old rtld on i386. Patch also contains bits for amd64 that I did not
> > > > > > > > > > > > tested yet. All other arches are not buildable for now.
> > > > > > > > > > > > 
> > > > > > > > > > > > Patch completely eliminates sysctl syscalls from the rtld and libc
> > > > > > > > > > > > startup. Without the patch, a single run of /bin/ls did 6 sysctls,
> > > > > > > > > > > > with the patch, no sysctls is queried at all.
> > > > > > > > > > > > 
> > > > > > > > > > Comparing with the originally posted patch, I added support for all
> > > > > > > > > > architectures, tested amd64 and ia32 on amd64, and converted getpagesizes(3)
> > > > > > > > > > that added two more startup sysctls.
> > > > > > > > > > 
> > > > > > > > > > Would be nice to get a testing for at least some !x86 architectures
> > > > > > > > > > before the commit, I added some people who helped me in past, to the Cc:.
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > Doesn't look good on sparc64:
> > > > > > > > > <...>
> > > > > > > > > NFS ROOT: 192.168.1.40:/usr/data/nfsroot/sparc64
> > > > > > > > > dc1: link state changed to UP
> > > > > > > > > pid 24 (ifconfig), uid 0: exited on signal 11
> > > > > > > > > Segmentation fault
> > > > > > > > > Interface  IP-Address  Broadcast
> > > > > > > > > pid 29 (rcorder), uid 0: exited on signal 11
> > > > > > > > > Segmentation fault
> > > > > > > > > pid 30 (grep), uid 0: exited on signal 11
> > > > > > > > > Segmentation fault
> > > > > > > > > pid 31 (rcorder), uid 0: exited on signal 11
> > > > > > > > > Segmentation fault
> > > > > > > > >  
> > > > > > > > > pid 32 (date), uid 0: exited on signal 11
> > > > > > > > > Segmentation fault
> > > > > > > > > Jun 29 12:20:50 getty[36]: open /dev/ttyv3: No such file or directory
> > > > > > > > > <...>
> > > > > > > > > 
> > > > > > > > > Unfortunately, I currently lack the time to debug this.
> > > > > > > > 
> > > > > > > > Thank you.
> > > > > > > 
> > > > > > > Did yu have time to look at this problem?  It would be nice to have this
> > > > > > > in the tree.
> > > > > > 
> > > > > > I cannot move forward without the help from somebody having access to
> > > > > > sparc64 system where the problem is reproducable.
> > > > > 
> > > > > Do you have a debug version of the patch which outputs the necessary
> > > > > information?
> > > > 
> > > > I would suggest to build rtld and libc with debugging symbols and
> > > > get full backtrace from the faults.
> > > 
> > > v100# gdb /sbin/ifconfig ifconfig.core
> > > GNU gdb 6.1.1 [FreeBSD]
> > > Copyright 2004 Free Software Foundation, Inc.
> > > GDB is free software, covered by the GNU General Public License, and you are
> > > welcome to change it and/or distribute copies of it under certain conditions.
> > > Type "show copying" to see the conditions.
> > > There is absolutely no warranty for GDB.  Type "show warranty" for details.
> > > This GDB was configured as "sparc64-marcel-freebsd"...
> > > Core was generated by `ifconfig'.
> > > Program terminated with signal 11, Segmentation fault.
> > > Reading symbols from /lib/libbsdxml.so.4...done.
> > > Loaded symbols for /lib/libbsdxml.so.4
> > > Reading symbols from /lib/libjail.so.1...done.
> > > Loaded symbols for /lib/libjail.so.1
> > > Reading symbols from /lib/libsbuf.so.5...done.
> > > Loaded symbols for /lib/libsbuf.so.5
> > > Reading symbols from /lib/libipx.so.5...done.
> > > Loaded symbols for /lib/libipx.so.5
> > > Reading symbols from /lib/libc.so.7...done.
> > > Loaded symbols for /lib/libc.so.7
> > > Reading symbols from /libexec/ld-elf.so.1...done.
> > > Loaded symbols for /libexec/ld-elf.so.1
> > > #0  0x000000004089ebdc in getpagesizes (pagesize=0x7fdffffe2f8, nelem=1)
> > >     at /usr/home/marius/co/head/src/lib/libc/gen/getpagesizes.c:75
> > > 75                      while (nops > 0 && ps[nops - 1] == 0)
> > > (gdb) bt
> > > #0  0x000000004089ebdc in getpagesizes (pagesize=0x7fdffffe2f8, nelem=1)
> > >     at /usr/home/marius/co/head/src/lib/libc/gen/getpagesizes.c:75
> > > #1  0x00000000407f4314 in malloc_init ()
> > >     at /usr/home/marius/co/head/src/lib/libc/stdlib/malloc.c:5418
> > > #2  0x00000000407f67d8 in malloc (size=32)
> > >     at /usr/home/marius/co/head/src/lib/libc/stdlib/malloc.c:5932
> > > #3  0x00000000001069ac in clone_setdefcallback (ifprefix=0x11b8a8 "wlan", 
> > >     p=0x10a1a0 <wlan_create>)
> > >     at /usr/home/marius/co/head/src/sbin/ifconfig/ifclone.c:106
> > > #4  0x0000000000119864 in __do_global_ctors_aux ()
> > > #5  0x000000000010243c in _init ()
> > > #6  0x0000000000102508 in _start ()
> > > #7  0x000000004022719c in .rtld_start ()
> > >     at /usr/home/marius/co/head/src/libexec/rtld-elf/sparc64/rtld_start.S:59
> > > #8  0x000000004022719c in .rtld_start ()
> > >     at /usr/home/marius/co/head/src/libexec/rtld-elf/sparc64/rtld_start.S:59
> > > Previous frame identical to this frame (corrupt stack?)
> > > 
> > > All faults I've looked at died the same why.
> > Thank you. I think I found the reason, which was an unitialized
> > variable. I also fixed a sillyness with osrelver.
> > 
> > In the patched tree, there is tools/test/auxinfo that could be used to
> > quick-check the system.
> > 
> > Updated patch is available at
> > http://people.freebsd.org/~kib/misc/rtld_auxinfo.1.patch
> 
> I can confirm that this versions works on sparc64.
After the discussion with Alexander, I made the change to allow libc to
access aux vectors, instead of providing rtld interface to fetch values.

I decided to keep the single function that fetch the values, because it
is convenient place to do digesting of the vector.

http://people.freebsd.org/~kib/misc/rtld_auxinfo.2.patch
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