Re: [PATCH] Ignore the first entry returned by svr4_current_sos_via_xfer_libraries for dynamically linked programs

Ben Cheng
2013-06-04T20:45:26Z

And it looks like reversing the order of checks for lm_prev and
libname in gdbserver/linux_qxfer_libraries_svr4:linux_qxfer_libraries_svr4()
is a possible fix for this problem.

On Tue, Jun 4, 2013 at 1:36 PM, Ben Cheng <bccheng@google.com> wrote:
> Perfect timing. :) I was playing with Android's dynamic linker and
> fount out that after setting the l_name field to NULL for the first
> entry gdb/gdbserver 7.6 start to work on Android.
>
> diff --git a/linker/linker.cpp b/linker/linker.cpp
> index c97b712..ddc16d8 100644
> --- a/linker/linker.cpp
> +++ b/linker/linker.cpp
> @@ -1644,7 +1644,8 @@ static Elf32_Addr __linker_init_post_relocation(KernelArgu
> link_map_t* map = &(si->link_map);
>
> map->l_addr = 0;
> - map->l_name = args.argv[0];
> + //map->l_name = args.argv[0];
> + map->l_name = NULL;
> map->l_prev = NULL;
> map->l_next = NULL;
>
> Thanks,
> -Ben
>
> On Tue, Jun 4, 2013 at 1:23 PM, Jan Kratochvil
> <jan.kratochvil@redhat.com> wrote:
>> On Tue, 04 Jun 2013 20:18:10 +0200, Ben Cheng wrote:
>>> Hmm this problem only shows up after I refresh gdbserver from the
>>> unmodified gdb 7.6 tree. As you mentioned, gdb 7.1 did not support
>>> library-list-svr4, so when I paired gdbserver 7.1 with gdb 7.6 they
>>> also work fine.
>>
>> In such case there is a bug in FSF gdbserver as it ignores only entries with
>> name "". Normal glibc uses name "" for the first entry for the executable but
>> Android Bionic apparently uses "<test_program>" as the first entry instead.
>>
>> The bug is in gdbserver/linux-low.c linux_qxfer_libraries_svr4() which should
>> always ignore the first entry, even if it is not "".
>>
>> The test IGNORE_FIRST does not need to be done there. The check
>> /* Assume that everything is a library if the dynamic loader was loaded
>> late by a static executable. */
>> if (exec_bfd && bfd_get_section_by_name (exec_bfd, ".dynamic") == NULL)
>>
>> is in fact already done by gdbserver/linux-low.c get_dynamic(): If PT_DYNAMIC
>> (".dynamic") is not found gdbserver will never send <library-list-svr4/> and
>> solib-svr4.c falls back to the memory reads where it copes with static
>> executables fine.
>>
>>
>> Thanks,
>> Jan