Debugging rtld

[Jeremie Le Hen]

Hi,

On Sat, May 17, 2008 at 01:26:53PM +0300, Kostik Belousov wrote:
> On Sat, May 17, 2008 at 11:17:40AM +0200, Jeremie Le Hen wrote:
> > I tried to compile my source tree with -fstack-protector-all, and it
> > happens that rtld breaks with this: once the new rtld is installed every
> > single problem coredumps.  I tried to compile rtld-elf without SSP, but
> > it didn't solve the problem.  Then I had to compile libc_pic.a without
> > SSP and it worked, but I don't understand the root of the problem.
> > So I want to use the generated coredump for post-mortem analysis with
> > gdb.
> > 
> > I compiled world with DEBUG_FLAGS=-g.  But GDB gives me a backtrace so
> > long that it can't be real.  Moreoever it doesn't seem to bring in the
> > required symbols.  I'm a GDB novice, so I'd like some help.
> > 
> > chroot> ===> libexec/rtld-elf (install)
> > chroot> chflags noschg /usr/libexec/ld-elf.so.1
> > chroot> install -s -o root -g wheel -m 555  -C -b -fschg -S ld-elf.so.1 /libexec
> > chroot> install -o root -g wheel -m 444 rtld.1.gz  /usr/share/man/man1
> > chroot> *** Signal 11
> > chroot>
> > chroot> jarjarbinks# cd /root; ls
> > chroot> Segmentation fault
> > 
> > host> jarjarbinks:145# ls -l /space/chroot/root/ls.core 
> > host> -rw-------  1 root  wheel  184320 May 17 10:19 /space/chroot/root/ls.core
> > host> jarjarbinks:149# gdb -c /space/chroot/root/ls.core -e /space/chroot/bin/ls
> > host> GNU gdb 6.1.1 [FreeBSD]
> > host> [...]
> > host> This GDB was configured as "i386-marcel-freebsd".
> > host> Core was generated by `ls'.
> > host> Program terminated with signal 11, Segmentation fault.
> > host> #0  0x280583e4 in ?? ()
> > host> (gdb) bt
> > host> #0  0x280583e4 in ?? ()
> > host> #1  0x00000000 in ?? ()
> > host> #2  0x00000000 in ?? ()
> > host> #3  0x00000000 in ?? ()
> > host> #4  0x00000000 in ?? ()
> > host> #5  0x00000000 in ?? ()
> > host> #6  0x00000000 in ?? ()
> > host> #7  0x00000000 in ?? ()
> > host> #8  0x00000000 in ?? ()
> > host> #9  0x00000000 in ?? ()
> > host> #10 0x00000000 in ?? ()
> > host> #11 0xffffffff in ?? ()
> > host> #12 0x00001000 in ?? ()
> > host> [...]
> > host> #359 0x73763a68 in ?? ()
> > host> #360 0x5b455c3d in ?? ()
> > host> [...]
> > host> #855 0x00000000 in ?? ()
> > host> [...]
> > 
> > Any hint on how to proceed would be welcome.
> 
> I usually add the CFLAGS+=-g to the rtld-elf/Makefile. Also, you do not
> need to bring down the whole host by the broken ld.so.1. Do not install
> it at all, and specify the path to the rtld by the --dynamic-linker switch,
> see into ld.

Thank you for this tip.  However the backtrace is still unusable.
I've recompiled libc_pic.a with -g, then rtld-elf with -g and finally
/bin/ls with you tip and -g.

I'm really brought to a standstill here.

Thank you.
Best regards,
-- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >