Re: [PATCH v3] nptl_db: Support different libpthread/ld.so load orders (bug 27744)

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 04/22/2021 13:44, Szabolcs Nagy via Gdb-patches wrote:
> The 04/22/2021 13:55, Florian Weimer wrote:
> > * Szabolcs Nagy:
> > > The 04/22/2021 10:05, Szabolcs Nagy via Gdb-patches wrote:
> > >> The 04/22/2021 10:33, Florian Weimer wrote:
> > >> > * Szabolcs Nagy:
> > >> > > on the aarch64 buildbot i see
> > >> > >
> > >> > > FAIL: nptl/tst-pthread-gdb-attach
> > >> > >
> > >> > > $ cat nptl/tst-pthread-gdb-attach.out
> > >> > > +set debug libthread-db 1
> > >> > > +add-symbol-file /work/glibc-aarch64-linux/build/build/nptl/tst-pthread-gdb-attach
> > >> > > add symbol table from file "/work/glibc-aarch64-linux/build/build/nptl/tst-pthread-gdb-attach"
> > >> > > +set auto-load safe-path /work/glibc-aarch64-linux/build/build/nptl_db
> > >> > > +set libthread-db-search-path /work/glibc-aarch64-linux/build/build/nptl_db
> > >> > > +attach 461328
> > >> > > [New LWP 461329]
> > >> > > Trying host libthread_db library: /work/glibc-aarch64-linux/build/build/nptl_db/libthread_db.so.1.
> > >> > > td_ta_new failed: application not linked with libthread
> > >> > > thread_db_load_search returning 0
> > >> > 
> > >> > Unfortunately I cannot reproduce this with binutils 2.30, GDB 8.2 and
> > >> > GCC 8.4.1.  Has your environment newer or older versions?
> > >> 
> > >> ubuntu flavour of
> > >> 
> > >> gcc 8.2.0
> > >> binutils 2.31.1
> > >> gdb 8.2
> > >> 
> > >> happens on armhf and aarch64 too.
> > >
> > > happens with gcc-10.2.0, gdb-9.2, binutils-2.34 too
> > > (still ubuntu)
> > 
> > Still no luck with binutils 2.35.1, a GCC 11 snapshot, and GDB 10.1.
> > 
> > Do you run this test as a regular user?  Could it be caused by YAMA
> > ptrace policies?
> 
> $ cat /proc/sys/kernel/yama/ptrace_scope
> 0
> 
> and the -static test passes so there gdb works.
> i can reproduce it on all ubuntu setups i have.

if i rerun the link command of the test exe but with -no-pie
instead of -pie then the test passes with that binary.

i suspect gdb places the breakpoint at the wrong place in pie
for some reason. can be ubuntu tooling specific. see the
breakpoint location (the exe base offset is missing):

+attach 1254516
[New LWP 1254517]
Trying host libthread_db library: /home/szabolcs/try/build/nptl_db/libthread_db.so.1.
td_ta_new failed: application not linked with libthread
thread_db_load_search returning 0
Trying host libthread_db library: /home/szabolcs/try/build/nptl_db/libthread_db.so.1.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/home/szabolcs/try/build/nptl_db/libthread_db.so.1".
thread_db_load_search returning 1
0x0000ffff9d3d89c4 in __futex_abstimed_wait_common64 (futex_word=0xffff9d363210, expected=1254517, clockid=<optimized out>, abstime=0x0, private=<optimized out>, cancel=cancel@entry=true) at futex-internal.c:74
74          err = INTERNAL_SYSCALL_CANCEL (futex_time64, futex_word, op, expected,
+break debugger_inspection_point
Breakpoint 1 at 0x20c0: file tst-pthread-gdb-attach.c, line 123.
+continue