Help with stepping into shared-library with stripped ld-linux on arm board

Hello, gdb experts.

Recently we are trying to stepping into shared-library on
arm board
using GDB 6.3 with gdbserver

First we find ld-linux.so is stripped so that gdb cannot
insert a
breakpoint at _dl_debug_state. Then it has to continue with
SINGLE_STEP
out of the linker codes, which is quite slow!!
Then one option we used is to re-compile the glibc with
symbol info and
put it into arm board, then it works.

But that's not final one, because eventually all the libs
and exes in
arm board have to be pre-linked for performance, so we have
to figure
out ways to debug shared-library with a stripped &
pre-linked ld-linux.
What we did is modify the enable_break() in solib-srv4.c and
return a
hard-coded address for _dl_debug_state, since it is
pre-linked and the
address is known.
But it turns out not work, and it looks gdb still has to
continue with
SINGLE_STEP out of the linker codes. I checked the gdbserver
using
strace, it looks the breakpoint in LD is inserted using
PTRACE_POKETEXT
in the correct address, don't know why it not work.

Any clue about this? What makes gdb decide to send
SINGLE_STEP or CONT
to gdbserver during stepping into a shared library? It looks
it keep
sending SINGLE_STEP command to gdbserver, till out of linker
code. Do I
miss something besides enable_break() in solib-srv4.c?

Your help is greatly appreciated!


Best Regards
Haojun 

On Thu, Mar 22, 2007 at 11:29:14PM +0800, Xu Haojun-a18535
wrote:
> Hello, gdb experts.
> 
> Recently we are trying to stepping into shared-library
on arm board
> using GDB 6.3 with gdbserver
> 
> First we find ld-linux.so is stripped so that gdb
cannot insert a
> breakpoint at _dl_debug_state. Then it has to continue
with SINGLE_STEP
> out of the linker codes, which is quite slow!!
> Then one option we used is to re-compile the glibc with
symbol info and
> put it into arm board, then it works.

I suggest you have two copies of your root filesystem. 
Point GDB at
one on your host that is not stripped, and run one that is
exactly the
same but stripped on the target.  Then everything will work
much
better.

> Any clue about this? What makes gdb decide to send
SINGLE_STEP or CONT
> to gdbserver during stepping into a shared library? It
looks it keep
> sending SINGLE_STEP command to gdbserver, till out of
linker code. Do I
> miss something besides enable_break() in solib-srv4.c?

It needs to know what function it's in to recognize shared
library
trampolines.  Without symbols, it's not going to work.

A compromise which might help is to use strip -g for ld.so
and
libpthread.so on your target instead of strip; that will
leave the
symbol tables, and remove only the debug info.

-- 
Daniel Jacobowitz
CodeSourcery

On Fri, Mar 23, 2007 at 06:56:55PM +0800, Xu Haojun-a18535
wrote:
> But this try seems not work, it still takes a long time
when
> stepping into shared-library, we are really confused
where goes wrong,
> it there any other place which controls the
shared-library stepping
> behavior besides enable_break() in solib-srv4.c ?

You've already asked this question and I've already answered
it.
There are a lot of things that will go wrong without
symbols.

I suspect this one is related to "fixup".


-- 
Daniel Jacobowitz
CodeSourcery

Daniel,

I know your solution and it works really.

But actually we are trying to figure out ways to debug an
arm board with ld-linux.so stripped of all symbols. 
"There are a lot of things that will go wrong without
symbols." That's exactly what we want to make clear -
how the symbols of ld-linux.so is used in gdb and where will
go wrong without these symbols.
So that we can figure out ways to serve our special reqs. 
Any clue about this?

Best Regards
Haojun

> -----Original Message-----
> From: Daniel Jacobowitz [mailto:drowfalse.org]
> Sent: 2007Äê3ÔÂ23ÈÕ 19:55
> To: Xu Haojun-a18535
> Cc: Michael Snyder; gdbsourceware.org; Xie
ShaoHua-A22496
> Subject: Re: Help with stepping into shared-library
with strippedld-linuxon arm
> board
> 
> On Fri, Mar 23, 2007 at 06:56:55PM +0800, Xu
Haojun-a18535 wrote:
> > But this try seems not work, it still takes a long
time when
> > stepping into shared-library, we are really
confused where goes wrong,
> > it there any other place which controls the
shared-library stepping
> > behavior besides enable_break() in solib-srv4.c ?
> 
> You've already asked this question and I've already
answered it.
> There are a lot of things that will go wrong without
symbols.
> 
> I suspect this one is related to "fixup".
> 
> 
> --
> Daniel Jacobowitz
> CodeSourcery

On Fri, Mar 23, 2007 at 09:10:56PM +0800, Xu Haojun-a18535
wrote:
> Daniel,
> 
> I know your solution and it works really.
> 
> But actually we are trying to figure out ways to debug
an arm board with ld-linux.so stripped of all symbols. 
> "There are a lot of things that will go wrong
without symbols." That's exactly what we want to make
clear - how the symbols of ld-linux.so is used in gdb and
where will go wrong without these symbols.
> So that we can figure out ways to serve our special
reqs. 
> Any clue about this?

No.

-- 
Daniel Jacobowitz
CodeSourcery