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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