Re: [PATCH v4] gdb, gdbserver: support dlmopen()

[Pedro Alves <pedro@palves.net>]

On 2021-11-17 14:28, Markus Metzger via Gdb-patches wrote:
> This patch was originally developed by H.J.  Last version:
> https://sourceware.org/pipermail/gdb-patches/2021-October/182353.html
> 

Should the commit have a Co-Authored-By: tag for H.J.?

> Changes in v4:
> 
> 1. add gdb.base/dlmopen.exp
> 2. extend svr4_same() to compare the load offset in addition to the name
> 3. supply l_addr_inferior for default DSO to make it work with #2
> 4. fix bugs in gdbserver/linux-low.cc
> 
> Changes in v3:
> 
> 1. Fix gdbserver support.
> 
> Changes in v2:
> 
> 1. Don't check shared libraries in other namespaces when updating shared
> libraries in a new namespace.
> 
> Regression-tested on x86-64 linux.
> 
> ---
> 
> In glibc, the r_debug structure contains (amongst others) the following
> fields:
> 
>   int r_version:
>     Version number for this protocol.  It should be greater than 0.
> 
> If r_version is 2, struct r_debug is extended to struct r_debug_extended
> with one additional field:
> 
>   struct r_debug_extended *r_next;
>     Link to the next r_debug_extended structure.  Each r_debug_extended
>     structure represents a different namespace.  The first r_debug_extended
>     structure is for the default namespace.
> 
> 1. Change solib_svr4_r_map argument to take the debug base.
> 2. Add solib_svr4_r_next to find the link map in the next namespace from
> the r_next field.
> 3. Update svr4_current_sos_direct to get the link map in the next namespace
> from the r_next field.
> 4. Don't check shared libraries in other namespaces when updating shared
> libraries in a new namespace.
> 5. Update svr4_same to check the load offset in addition to the name
> 6. Update svr4_default_sos to also set l_addr_inferior
> 
> Add gdb.base/dlmopen.exp to test this.

I'm wondering whether ideally symbol lookup would be updated to handle
different namespaces.  I'm thinking of for example
svr4_iterate_over_objfiles_in_search_order.


Can you describe what xml changes were necessary?  Do we need to update
the manual where the xml/packet are described?


> +++ b/gdb/testsuite/gdb.base/dlmopen.exp
> @@ -0,0 +1,141 @@
> +# This testcase is part of GDB, the GNU debugger.
> +#
> +# Copyright 2021 Free Software Foundation, Inc.
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +

Please a short description of what is being tested, here.

> +clean_restart $binfile
> +
> +# Start the test program.
> +set test_spawn_id [spawn_wait_for_attach $binfile]
> +set testpid [spawn_id_get_pid $test_spawn_id]
> +
> +# Attach.
> +gdb_test "attach $testpid" "Attaching to program.*, process $testpid.*"

Seems like a can_spawn_for_attach check is missing.

> +
> +with_test_prefix "attach" {
> +    # Remove the pause.  We no longer need it.
> +    gdb_test "print pause = 0" "\\\$1 = 0"
> +
> +    # Set the same breakpoints again.  This time, however, we do not allow the
> +    # breakpoint to be pending since the library has already been loaded.
> +    gdb_breakpoint $srcfile_lib:$bp_inc
> +    gdb_breakpoint $srcfile:$bp_main
> +
> +    test_dlmopen
> +}