Date: Wed, 23 Jan 2019 10:10:43 -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: <20B92DA0-33B7-44D1-AB92-E3DD55A8B7CE@yahoo.com> In-Reply-To: <DBF4C75D-213E-42E2-8682-6B3078FCB8D5@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> <a0e02258-3e43-fb91-566d-29b48fe81e77@FreeBSD.org> <DBF4C75D-213E-42E2-8682-6B3078FCB8D5@yahoo.com>
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On 2019-Jan-23, at 09:59, Mark Millard <marklmi at yahoo.com> wrote: > On 2019-Jan-23, at 09:02, John Baldwin <jhb at FreeBSD.org> wrote: >=20 >> 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). >=20 > I buildworld buildkernel with debug symbols for both and install them: >=20 > # 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 >=20 > # 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 >=20 > So I think the first TRY clause does not work. >=20 > In the tested gdb used on the a.out I'm testing I get: >=20 > (gdb) p &((Obj_Entry *)0)->linkmap > No symbol "Obj_Entry" in current context. >=20 > gdb does not report reading symbols from or for: >=20 > /usr/lib/debug/libexec/ld-elf.so.1.debug > or: > /usr/libexec/ld-elf.so.1 > or: > /libexec/ld-elf.so.1 >=20 > It only reports reading them from/for the a.out . It neded up that I had a littel time so . . . I tried /usr/local/bin/gdb and for it: (gdb) p &((Obj_Entry *)0)->linkmap $1 =3D (struct link_map *) 0x238 So the lack of finding Obj_Entry via the test gdb seems to be specific to the test gdb, not a problem for devel/gdb . May be the test gdb has some sort of build problem in my context, given that I used CPATH to get things to build? =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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