Date: Wed, 23 Jan 2019 09:59:57 -0800 From: Mark Millard <marklmi@yahoo.com> To: John Baldwin <jhb@FreeBSD.org> Cc: "freebsd-ppc@freebsd.org" <freebsd-ppc@FreeBSD.org> Subject: Re: GDB TLS testing [actually running some tests finally: a success with -pthread used] Message-ID: <DBF4C75D-213E-42E2-8682-6B3078FCB8D5@yahoo.com> In-Reply-To: <a0e02258-3e43-fb91-566d-29b48fe81e77@FreeBSD.org> References: <b0f5b62f-54fb-309f-a578-7b4d9e340a55@FreeBSD.org> <19343397-859C-4629-A4A5-B0DCDE25957B@yahoo.com> <AB56B3D1-1762-4115-B7B4-91D4B997F1C4@yahoo.com> <eff896f3-e385-9a12-5132-3884e69689ca@FreeBSD.org> <D0B83B01-5428-42F0-B785-221826AF7EC4@yahoo.com> <a1da2471-535d-1497-ddf3-93aa0d29df59@FreeBSD.org> <5AA68ED2-2615-438B-A6AE-406CBD8E49F7@yahoo.com> <20027C29-0093-4001-A135-23783F8B87F3@yahoo.com> <4048D2A4-7E14-481C-9B5D-00567BCF4463@yahoo.com> <2AAC9738-73BD-475A-888A-252EE853A5C6@yahoo.com> <493AC0BE-3EC6-42B7-B027-FFB6454761B5@yahoo.com> <B07EC3F9-6C08-4B5D-89D0-4048AF305A2D@yahoo.com> <52E66D9B-C332-4565-B8E7-F54F6454B062@yahoo.com> <a0e02258-3e43-fb91-566d-29b48fe81e77@FreeBSD.org>
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On 2019-Jan-23, at 09:02, John Baldwin <jhb at FreeBSD.org> wrote:
> On 1/23/19 12:19 AM, Mark Millard wrote:
>>
>>
>> On 2019-Jan-22, at 22:53, Mark Millard <marklmi@yahoo.com> wrote:
>>
>>
>>
>>> On 2019-Jan-22, at 19:19, Mark Millard <marklmi at yahoo.com> wrote:
>>>
>>>
>>>
>>>> On 2019-Jan-22, at 18:32, Mark Millard <marklm at yahoo.com> wrote:
>>>>
>>>>
>>>>
>>>>> On 2019-Jan-22, at 17:06, Mark Millard <marklmi at yahoo.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> . . .
>>>>> So I'm trying:
>>>>>
>>>>> # git clean -f
>>>>> # rm */config.cache */*/config.cache
>>>>> # env CPATH=/usr/local/include ./configure
>>>>> . . .
>>>>> # env CPATH=/usr/local/include gmake
>>>>> . . .
>>>>>
>>>>> in order to try to add paths after the command line -I paths.
>>>>>
>>>>> . . . This looks like it built. I've not used the build yet.
>>>>>
>>>>
>>>> Looking at a *.core did not go well for my context:
>>>>
>>>> # cc -g -O2 tls_gdb_test.c
>>>> tls_gdb_test.c:16:2: warning: indirection of non-volatile null pointer will be deleted, not trap [-Wnull-dereference]
>>>> *(char *)NULL = 1;
>>>> ^~~~~~~~~~~~~
>>>> tls_gdb_test.c:16:2: note: consider using __builtin_trap() or qualifying pointer with 'volatile'
>>>> 1 warning generated.
>
> For me, builtin_trap didn't DTRT on ppc before, but that was probably using
> gcc rather than clang (and possibly using gcc4.2).
>
>>>> . . .
>>>
>>>
>>> So far all tried-combinations of using gcc versions for build
>>> the test program and/or building the gdb used do not work for
>>> "p id" and "p &id" in doing the test. clang is not essential
>>> to the behavior observed.
>>
>> Using "-g -O2 -pthread" to build the test program via system
>> clang or gcc8 (for example) did lead to the likes of:
>>
>> (gdb) run
>> Starting program: /root/c_tests/a.out
>> main: PID 15350
>> id = 15350 (0x810055020)
>>
>> ^C
>> Program received signal SIGINT, Interrupt.
>> main (ac=<optimized out>, av=<optimized out>) at tls_gdb_test.c:16
>> 16 *(char *)NULL = 1;
>> (gdb) bt
>> #0 main (ac=<optimized out>, av=<optimized out>) at tls_gdb_test.c:16
>> (gdb) info threads
>> Id Target Id Frame
>> * 1 LWP 100324 of process 15350 main (ac=<optimized out>, av=<optimized out>) at tls_gdb_test.c:16
>> (gdb) p id
>> $1 = 15350
>> (gdb) p &id
>> $2 = (int *) 0x810055020
>>
>> So it appears one branch of:
>>
>> static void
>> fbsd_fetch_rtld_offsets (struct gdbarch *gdbarch, struct fbsd_pspace_data *data)
>> {
>> TRY
>> {
>> /* Fetch offsets from debug symbols in rtld. */
>> data->off_linkmap = parse_and_eval_long ("&((Obj_Entry *)0)->linkmap");
>> data->off_tlsindex = parse_and_eval_long ("&((Obj_Entry *)0)->tlsindex");
>> data->rtld_offsets_valid = true;
>> return;
>> }
>> CATCH (e, RETURN_MASK_ERROR)
>> {
>> data->off_linkmap = -1;
>> }
>> END_CATCH
>>
>> TRY
>> {
>> /* Fetch offsets from global variables in libthr. Note that
>> this does not work for single-threaded processes that are not
>> linked against libthr. */
>> data->off_linkmap = fbsd_read_integer_by_name(gdbarch,
>> "_thread_off_linkmap");
>> data->off_tlsindex = fbsd_read_integer_by_name(gdbarch,
>> "_thread_off_tlsindex");
>> data->rtld_offsets_valid = true;
>> return;
>> }
>> CATCH (e, RETURN_MASK_ERROR)
>> {
>> data->off_linkmap = -1;
>> }
>> END_CATCH
>> }
>>
>> is working when -pthread is used.
>
> Yes. The second one only works for programs linked against -lthr. Otherwise
> you need to have built your system with debug symbols (which is the default),
> and gdb needs to be able to access /usr/lib/debug/libexec/ld-elf.so.1.debug
> to determine the offsets of the two fields in Obj_Entry (this is what the
> first TRY clause does).
I buildworld buildkernel with debug symbols for both and install them:
# ls -lT /usr/lib/debug/libexec/ld-elf.so.1.debug
-r--r--r-- 1 root wheel 576344 Dec 11 22:58:11 2018 /usr/lib/debug/libexec/ld-elf.so.1.debug
# ls -lT /usr/libexec/ld-elf.so.1 /libexec/ld-elf.so.1
-r-xr-xr-x 1 root wheel 184400 Dec 9 02:35:05 2018 /libexec/ld-elf.so.1
lrwxr-xr-x 1 root wheel 25 Dec 11 22:58:12 2018 /usr/libexec/ld-elf.so.1 -> ../../libexec/ld-elf.so.1
So I think the first TRY clause does not work.
In the tested gdb used on the a.out I'm testing I get:
(gdb) p &((Obj_Entry *)0)->linkmap
No symbol "Obj_Entry" in current context.
gdb does not report reading symbols from or for:
/usr/lib/debug/libexec/ld-elf.so.1.debug
or:
/usr/libexec/ld-elf.so.1
or:
/libexec/ld-elf.so.1
It only reports reading them from/for the a.out .
===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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