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:
>>=20
>>=20
>> On 2019-Jan-22, at 22:53, Mark Millard <marklmi@yahoo.com> wrote:
>>=20
>>=20
>>=20
>>> On 2019-Jan-22, at 19:19, Mark Millard <marklmi at yahoo.com> wrote:
>>>=20
>>>=20
>>>=20
>>>> On 2019-Jan-22, at 18:32, Mark Millard <marklm at yahoo.com> wrote:
>>>>=20
>>>>=20
>>>>=20
>>>>> On 2019-Jan-22, at 17:06, Mark Millard <marklmi at yahoo.com> =
wrote:
>>>>>=20
>>>>>=20
>>>>>=20
>>>>> . . .
>>>>> So I'm trying:
>>>>>=20
>>>>> # git clean -f
>>>>> # rm */config.cache */*/config.cache
>>>>> # env CPATH=3D/usr/local/include ./configure
>>>>> . . .
>>>>> # env CPATH=3D/usr/local/include gmake
>>>>> . . .
>>>>>=20
>>>>> in order to try to add paths after the command line -I paths.
>>>>>=20
>>>>> . . . This looks like it built. I've not used the build yet.
>>>>>=20
>>>>=20
>>>> Looking at a *.core did not go well for my context:
>>>>=20
>>>> # cc -g -O2 tls_gdb_test.c=20
>>>> tls_gdb_test.c:16:2: warning: indirection of non-volatile null =
pointer will be deleted, not trap [-Wnull-dereference]
>>>> *(char *)NULL =3D 1;
>>>> ^~~~~~~~~~~~~
>>>> tls_gdb_test.c:16:2: note: consider using __builtin_trap() or =
qualifying pointer with 'volatile'
>>>> 1 warning generated.
>=20
> For me, builtin_trap didn't DTRT on ppc before, but that was probably =
using
> gcc rather than clang (and possibly using gcc4.2).
>=20
>>>> . . .
>>>=20
>>>=20
>>> 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.
>>=20
>> Using "-g -O2 -pthread" to build the test program via system
>> clang or gcc8 (for example) did lead to the likes of:
>>=20
>> (gdb) run=20
>> Starting program: /root/c_tests/a.out=20
>> main: PID 15350
>> id =3D 15350 (0x810055020)
>>=20
>> ^C
>> Program received signal SIGINT, Interrupt.
>> main (ac=3D<optimized out>, av=3D<optimized out>) at =
tls_gdb_test.c:16
>> 16 *(char *)NULL =3D 1;
>> (gdb) bt
>> #0 main (ac=3D<optimized out>, av=3D<optimized out>) at =
tls_gdb_test.c:16
>> (gdb) info threads
>> Id Target Id Frame=20
>> * 1 LWP 100324 of process 15350 main (ac=3D<optimized out>, =
av=3D<optimized out>) at tls_gdb_test.c:16
>> (gdb) p id
>> $1 =3D 15350
>> (gdb) p &id
>> $2 =3D (int *) 0x810055020
>>=20
>> So it appears one branch of:
>>=20
>> 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 =3D parse_and_eval_long ("&((Obj_Entry =
*)0)->linkmap");
>> data->off_tlsindex =3D parse_and_eval_long ("&((Obj_Entry =
*)0)->tlsindex");
>> data->rtld_offsets_valid =3D true;
>> return;
>> }
>> CATCH (e, RETURN_MASK_ERROR)
>> {
>> data->off_linkmap =3D -1;
>> }
>> END_CATCH
>>=20
>> 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 =3D fbsd_read_integer_by_name(gdbarch,
>> =
"_thread_off_linkmap");
>> data->off_tlsindex =3D fbsd_read_integer_by_name(gdbarch,
>> =
"_thread_off_tlsindex");
>> data->rtld_offsets_valid =3D true;
>> return;
>> }
>> CATCH (e, RETURN_MASK_ERROR)
>> {
>> data->off_linkmap =3D -1;
>> }
>> END_CATCH
>> }
>>=20
>> is working when -pthread is used.
>=20
> 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 .
=
=20
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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