Date: Wed, 23 Jan 2019 09:02:44 -0800 From: John Baldwin <jhb@FreeBSD.org> To: Mark Millard <marklmi@yahoo.com> 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: <a0e02258-3e43-fb91-566d-29b48fe81e77@FreeBSD.org> In-Reply-To: <52E66D9B-C332-4565-B8E7-F54F6454B062@yahoo.com> 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>
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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).
--
John Baldwin
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