[uml-devel] Re: tt mode tls/glibc crash with 2.6 (Was: Re: uml-patch-2.6.0)

[M A Young <m.a.young@durham.ac.uk>]

On Fri, 23 Jan 2004, M A Young wrote:

> I now know where 0xbeffe018 comes from. The endless segfault is triggered
> from line 1256 of elf/rtld.c in the glibc code (1252-1258 are shown from
> RedHat's glibc-2.3.2-101.4.i686.rpm package)
>
> #ifdef NEED_DL_SYSINFO
>   if (GL(dl_sysinfo_dso) != NULL)
>     {
>       /* We have a prelinked DSO preloaded by the system.  */
>       GL(dl_sysinfo) = GL(dl_sysinfo_dso)->e_entry;
>
>       /* Do an abridged version of the work _dl_map_object_from_fd would do
>
>
> GL(dl_sysinfo_dso) is _dl_sysinfo_dso, _rtld_local._dl_sysinfo_dso or
> _rtld_global._dl_sysinfo_dso according to context
>
> _dl_sysinfo_dso=0 is at 0xa0603f50
> _rtld_local._dl_sysinfo_dso=0xbeffe000 is at 0x40015454
> _rtld_global._dl_sysinfo_dso=0xbeffe000 is at 0x40015454
>
> so I am guessing that _rtld_{local,global}._dl_sysinfo_dso should have
> been initialized from _dl_sysinfo_dso but wasn't. This could be a glibc
> bug, though I haven't looked closely enough to be sure.

Further checking shows that _rtld_global._dl_sysinfo_dso is set from the
value of AT_SYSINFO_EHDR passed by the kernel. So UML tt mode is broken
because it doesn't seem to pass this value. However glibc is also broken,
because it should set _rtld_global._dl_sysinfo_dso=NULL by default in case
AT_SYSINFO_EHDR isn't passed to it by the kernel.

Anyway, I intend to test whether this is the problem tomorrow, either by
recompiling glibc (it is a one-line fix), or possibly using a hex editor
to hack the existing ld.so.

	Michael Young


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