307 lines
19 KiB
Diff
307 lines
19 KiB
Diff
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From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
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From: Simon Marchi <simon.marchi@polymtl.ca>
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Date: Tue, 8 Jun 2021 16:50:53 -0400
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Subject: gdb-rhbz1971095-libthread_db-update-1of5.patch
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;; Backport "gdb: try to load libthread_db only after reading all
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;; shared libraries when attaching / handling a fork child"
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;; (Simon Marchi, RH BZ 1971095)
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When trying to attach to a pthread process on a Linux system with glibc 2.33,
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we get:
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$ ./gdb -q -nx --data-directory=data-directory -p 1472010
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Attaching to process 1472010
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[New LWP 1472013]
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[New LWP 1472014]
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[New LWP 1472015]
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Error while reading shared library symbols for /usr/lib/libpthread.so.0:
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Cannot find user-level thread for LWP 1472015: generic error
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0x00007ffff6d3637f in poll () from /usr/lib/libc.so.6
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(gdb)
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When attaching to a process (or handling a fork child, an operation very
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similar to attaching), GDB reads the shared library list from the
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process. For each shared library (if "set auto-solib-add" is on), it
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reads its symbols and calls the "new_objfile" observable.
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The libthread-db code monitors this observable, and if it sees an
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objfile named somewhat like "libpthread.so" go by, it tries to load
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libthread_db.so in the GDB process itself. libthread_db knows how to
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navigate libpthread's data structures to get information about the
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existing threads.
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To locate these data structures, libthread_db calls ps_pglobal_lookup
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(implemented in proc-service.c), passing in a symbol name and expecting
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an address in return.
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Before glibc 2.33, libthread_db always asked for symbols found in
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libpthread. There was no ordering problem: since we were always trying
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to load libthread_db in reaction to processing libpthread (and reading
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in its symbols) and libthread_db only asked symbols from libpthread, the
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requested symbols could always be found. Starting with glibc 2.33,
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libthread_db now asks for a symbol name that can be found in
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/lib/ld-linux-x86-64.so.2 (_rtld_global). And the ordering in which GDB
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reads the shared libraries from the inferior when attaching is
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unfortunate, in that libpthread is processed before ld-linux. So when
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loading libthread_db in reaction to processing libpthread, and
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libthread_db requests the symbol that is from ld-linux, GDB is not yet
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able to supply it.
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That problematic symbol lookup happens in the thread_from_lwp function,
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when we call td_ta_map_lwp2thr_p, and an exception is thrown at this
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point:
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#0 0x00007ffff6681012 in __cxxabiv1::__cxa_throw (obj=0x60e000006100, tinfo=0x555560033b50 <typeinfo for gdb_exception_error>, dest=0x55555d9404bc <gdb_exception_error::~gdb_exception_error()>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_throw.cc:78
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#1 0x000055555e5d3734 in throw_it(return_reason, errors, const char *, typedef __va_list_tag __va_list_tag *) (reason=RETURN_ERROR, error=GENERIC_ERROR, fmt=0x55555f0c5360 "Cannot find user-level thread for LWP %ld: %s", ap=0x7fffffffaae0) at /home/simark/src/binutils-gdb/gdbsupport/common-exceptions.cc:200
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#2 0x000055555e5d37d4 in throw_verror (error=GENERIC_ERROR, fmt=0x55555f0c5360 "Cannot find user-level thread for LWP %ld: %s", ap=0x7fffffffaae0) at /home/simark/src/binutils-gdb/gdbsupport/common-exceptions.cc:208
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#3 0x000055555e0b0ed2 in verror (string=0x55555f0c5360 "Cannot find user-level thread for LWP %ld: %s", args=0x7fffffffaae0) at /home/simark/src/binutils-gdb/gdb/utils.c:171
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#4 0x000055555e5e898a in error (fmt=0x55555f0c5360 "Cannot find user-level thread for LWP %ld: %s") at /home/simark/src/binutils-gdb/gdbsupport/errors.cc:43
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#5 0x000055555d06b4bc in thread_from_lwp (stopped=0x617000035d80, ptid=...) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:418
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#6 0x000055555d07040d in try_thread_db_load_1 (info=0x60c000011140) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:912
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#7 0x000055555d071103 in try_thread_db_load (library=0x55555f0c62a0 "libthread_db.so.1", check_auto_load_safe=false) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1014
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#8 0x000055555d072168 in try_thread_db_load_from_sdir () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1091
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#9 0x000055555d072d1c in thread_db_load_search () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1146
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#10 0x000055555d07365c in thread_db_load () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1203
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#11 0x000055555d07373e in check_for_thread_db () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1246
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#12 0x000055555d0738ab in thread_db_new_objfile (objfile=0x61300000c0c0) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1275
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#13 0x000055555bd10740 in std::__invoke_impl<void, void (*&)(objfile*), objfile*> (__f=@0x616000068d88: 0x55555d073745 <thread_db_new_objfile(objfile*)>) at /usr/include/c++/10.2.0/bits/invoke.h:60
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#14 0x000055555bd02096 in std::__invoke_r<void, void (*&)(objfile*), objfile*> (__fn=@0x616000068d88: 0x55555d073745 <thread_db_new_objfile(objfile*)>) at /usr/include/c++/10.2.0/bits/invoke.h:153
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#15 0x000055555bce0392 in std::_Function_handler<void (objfile*), void (*)(objfile*)>::_M_invoke(std::_Any_data const&, objfile*&&) (__functor=..., __args#0=@0x7fffffffb4a0: 0x61300000c0c0) at /usr/include/c++/10.2.0/bits/std_function.h:291
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#16 0x000055555d3595c0 in std::function<void (objfile*)>::operator()(objfile*) const (this=0x616000068d88, __args#0=0x61300000c0c0) at /usr/include/c++/10.2.0/bits/std_function.h:622
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#17 0x000055555d356b7f in gdb::observers::observable<objfile*>::notify (this=0x555566727020 <gdb::observers::new_objfile>, args#0=0x61300000c0c0) at /home/simark/src/binutils-gdb/gdb/../gdbsupport/observable.h:106
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#18 0x000055555da3f228 in symbol_file_add_with_addrs (abfd=0x61200001ccc0, name=0x6190000d9090 "/usr/lib/libpthread.so.0", add_flags=..., addrs=0x7fffffffbc10, flags=..., parent=0x0) at /home/simark/src/binutils-gdb/gdb/symfile.c:1131
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#19 0x000055555da3f763 in symbol_file_add_from_bfd (abfd=0x61200001ccc0, name=0x6190000d9090 "/usr/lib/libpthread.so.0", add_flags=<error reading variable: Cannot access memory at address 0xffffffffffffffb0>, addrs=0x7fffffffbc10, flags=<error reading variable: Cannot access memory at address 0xffffffffffffffc0>, parent=0x0) at /home/simark/src/binutils-gdb/gdb/symfile.c:1167
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#20 0x000055555d95f9fa in solib_read_symbols (so=0x6190000d8e80, flags=...) at /home/simark/src/binutils-gdb/gdb/solib.c:681
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#21 0x000055555d96233d in solib_add (pattern=0x0, from_tty=0, readsyms=1) at /home/simark/src/binutils-gdb/gdb/solib.c:987
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#22 0x000055555d93646e in enable_break (info=0x608000008f20, from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2238
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#23 0x000055555d93cfc0 in svr4_solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:3049
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#24 0x000055555d96610d in solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib.c:1195
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#25 0x000055555cdee318 in post_create_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:318
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#26 0x000055555ce00e6e in setup_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:2439
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#27 0x000055555ce59c34 in handle_one (event=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:4887
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#28 0x000055555ce5cd00 in stop_all_threads () at /home/simark/src/binutils-gdb/gdb/infrun.c:5064
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#29 0x000055555ce7f0da in stop_waiting (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:8006
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#30 0x000055555ce67f5c in handle_signal_stop (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:6062
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#31 0x000055555ce63653 in handle_inferior_event (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:5727
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#32 0x000055555ce4f297 in fetch_inferior_event () at /home/simark/src/binutils-gdb/gdb/infrun.c:4105
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#33 0x000055555cdbe3bf in inferior_event_handler (event_type=INF_REG_EVENT) at /home/simark/src/binutils-gdb/gdb/inf-loop.c:42
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#34 0x000055555d018047 in handle_target_event (error=0, client_data=0x0) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:4060
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#35 0x000055555e5ea77e in handle_file_event (file_ptr=0x60600008b1c0, ready_mask=1) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:575
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#36 0x000055555e5eb09c in gdb_wait_for_event (block=0) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:701
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#37 0x000055555e5e8d19 in gdb_do_one_event () at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:212
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#38 0x000055555dd6e0d4 in wait_sync_command_done () at /home/simark/src/binutils-gdb/gdb/top.c:528
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#39 0x000055555dd6e372 in maybe_wait_sync_command_done (was_sync=0) at /home/simark/src/binutils-gdb/gdb/top.c:545
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#40 0x000055555d0ec7c8 in catch_command_errors (command=0x55555ce01bb8 <attach_command(char const*, int)>, arg=0x7fffffffe28d "1472010", from_tty=1, do_bp_actions=false) at /home/simark/src/binutils-gdb/gdb/main.c:452
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#41 0x000055555d0f03ad in captured_main_1 (context=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1149
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#42 0x000055555d0f1239 in captured_main (data=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1232
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#43 0x000055555d0f1315 in gdb_main (args=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1257
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#44 0x000055555bb70cf9 in main (argc=7, argv=0x7fffffffde88) at /home/simark/src/binutils-gdb/gdb/gdb.c:32
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The exception is caught here:
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#0 __cxxabiv1::__cxa_begin_catch (exc_obj_in=0x60e0000060e0) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_catch.cc:84
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#1 0x000055555d95fded in solib_read_symbols (so=0x6190000d8e80, flags=...) at /home/simark/src/binutils-gdb/gdb/solib.c:689
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#2 0x000055555d96233d in solib_add (pattern=0x0, from_tty=0, readsyms=1) at /home/simark/src/binutils-gdb/gdb/solib.c:987
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#3 0x000055555d93646e in enable_break (info=0x608000008f20, from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2238
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#4 0x000055555d93cfc0 in svr4_solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:3049
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#5 0x000055555d96610d in solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib.c:1195
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#6 0x000055555cdee318 in post_create_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:318
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#7 0x000055555ce00e6e in setup_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:2439
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#8 0x000055555ce59c34 in handle_one (event=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:4887
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#9 0x000055555ce5cd00 in stop_all_threads () at /home/simark/src/binutils-gdb/gdb/infrun.c:5064
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#10 0x000055555ce7f0da in stop_waiting (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:8006
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#11 0x000055555ce67f5c in handle_signal_stop (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:6062
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#12 0x000055555ce63653 in handle_inferior_event (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:5727
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#13 0x000055555ce4f297 in fetch_inferior_event () at /home/simark/src/binutils-gdb/gdb/infrun.c:4105
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#14 0x000055555cdbe3bf in inferior_event_handler (event_type=INF_REG_EVENT) at /home/simark/src/binutils-gdb/gdb/inf-loop.c:42
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#15 0x000055555d018047 in handle_target_event (error=0, client_data=0x0) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:4060
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#16 0x000055555e5ea77e in handle_file_event (file_ptr=0x60600008b1c0, ready_mask=1) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:575
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#17 0x000055555e5eb09c in gdb_wait_for_event (block=0) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:701
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#18 0x000055555e5e8d19 in gdb_do_one_event () at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:212
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#19 0x000055555dd6e0d4 in wait_sync_command_done () at /home/simark/src/binutils-gdb/gdb/top.c:528
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#20 0x000055555dd6e372 in maybe_wait_sync_command_done (was_sync=0) at /home/simark/src/binutils-gdb/gdb/top.c:545
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#21 0x000055555d0ec7c8 in catch_command_errors (command=0x55555ce01bb8 <attach_command(char const*, int)>, arg=0x7fffffffe28d "1472010", from_tty=1, do_bp_actions=false) at /home/simark/src/binutils-gdb/gdb/main.c:452
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#22 0x000055555d0f03ad in captured_main_1 (context=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1149
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#23 0x000055555d0f1239 in captured_main (data=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1232
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#24 0x000055555d0f1315 in gdb_main (args=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1257
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#25 0x000055555bb70cf9 in main (argc=7, argv=0x7fffffffde88) at /home/simark/src/binutils-gdb/gdb/gdb.c:32
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Catching the exception at this point means that the thread_db_info
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object for this inferior will be left in place, despite the failure to
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load libthread_db. This means that there won't be further attempts at
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loading libthread_db, because thread_db_load will think that
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libthread_db is already loaded for this inferior and will always exit
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early. To fix this, add a try/catch around calling try_thread_db_load_1
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in try_thread_db_load, such that if some exception is thrown while
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trying to load libthread_db, we reset / delete the thread_db_info for
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that inferior. That alone makes attach work fine again, because
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check_for_thread_db is called again in the thread_db_inferior_created
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observer (that happens after we learned about all shared libraries and
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their symbols), and libthread_db is successfully loaded then.
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When attaching, I think that the inferior_created observer is a good
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place to try to load libthread_db: it is called once everything has
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stabilized, when we learned about all shared libraries.
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The only problem then is that when we first try (and fail) to load
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libthread_db, in reaction to learning about libpthread, we show this
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warning:
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warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.
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This is misleading, because we do succeed in loading it later. So when
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attaching, I think we shouldn't try to load libthread_db in reaction to
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the new_objfile events, we should wait until we have learned about all
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shared libraries (using the inferior_created observable). To do so, add
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an `in_initial_library_scan` flag to struct inferior. This flag is used
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to postpone loading libthread_db if we are attaching or handling a fork
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child.
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When debugging remotely with GDBserver, the same problem happens, except
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that the qSymbol mechanism (allowing the remote side to ask GDB for
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symbols values) is involved. The fix there is the same idea, we make
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GDB wait until all shared libraries and their symbols are known before
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sending out a qSymbol packet. This way, we never present the remote
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side a state where libpthread.so's symbols are known but ld-linux's
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symbols aren't.
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gdb/ChangeLog:
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* inferior.h (class inferior) <in_initial_library_scan>: New.
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* infcmd.c (post_create_inferior): Set in_initial_library_scan.
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* infrun.c (follow_fork_inferior): Likewise.
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* linux-thread-db.c (try_thread_db_load): Catch exception thrown
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by try_thread_db_load_1
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(thread_db_load): Return early if in_initial_library_scan is
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set.
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* remote.c (remote_new_objfile): Return early if
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in_initial_library_scan is set.
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Change-Id: I7a279836cfbb2b362b4fde11b196b4aab82f5efb
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diff --git a/gdb/infcmd.c b/gdb/infcmd.c
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--- a/gdb/infcmd.c
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+++ b/gdb/infcmd.c
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@@ -313,6 +313,10 @@ post_create_inferior (struct target_ops *target, int from_tty)
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const unsigned solib_add_generation
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= current_program_space->solib_add_generation;
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+ scoped_restore restore_in_initial_library_scan
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+ = make_scoped_restore (¤t_inferior ()->in_initial_library_scan,
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+ true);
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+
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/* Create the hooks to handle shared library load and unload
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events. */
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solib_create_inferior_hook (from_tty);
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diff --git a/gdb/inferior.h b/gdb/inferior.h
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--- a/gdb/inferior.h
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+++ b/gdb/inferior.h
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@@ -511,6 +511,10 @@ class inferior : public refcounted_object
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architecture/description. */
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bool needs_setup = false;
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+ /* True when we are reading the library list of the inferior during an
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+ attach or handling a fork child. */
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+ bool in_initial_library_scan = false;
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+
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/* Private data used by the target vector implementation. */
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std::unique_ptr<private_inferior> priv;
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diff --git a/gdb/infrun.c b/gdb/infrun.c
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--- a/gdb/infrun.c
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+++ b/gdb/infrun.c
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@@ -540,6 +540,9 @@ holding the child stopped. Try \"set detach-on-fork\" or \
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breakpoint. If a "cloned-VM" event was propagated
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better throughout the core, this wouldn't be
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required. */
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+ scoped_restore restore_in_initial_library_scan
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+ = make_scoped_restore (&child_inf->in_initial_library_scan,
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+ true);
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solib_create_inferior_hook (0);
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}
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}
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@@ -675,6 +678,8 @@ holding the child stopped. Try \"set detach-on-fork\" or \
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shared libraries, and install the solib event breakpoint.
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If a "cloned-VM" event was propagated better throughout
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the core, this wouldn't be required. */
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+ scoped_restore restore_in_initial_library_scan
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+ = make_scoped_restore (&child_inf->in_initial_library_scan, true);
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solib_create_inferior_hook (0);
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}
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diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
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--- a/gdb/linux-thread-db.c
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+++ b/gdb/linux-thread-db.c
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@@ -1012,8 +1012,17 @@ try_thread_db_load (const char *library, bool check_auto_load_safe)
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if (strchr (library, '/') != NULL)
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info->filename = gdb_realpath (library).release ();
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- if (try_thread_db_load_1 (info))
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- return true;
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+ try
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+ {
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+ if (try_thread_db_load_1 (info))
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+ return true;
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+ }
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+ catch (const gdb_exception_error &except)
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+ {
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+ if (libthread_db_debug)
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+ exception_fprintf (gdb_stdlog, except,
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+ "Warning: While trying to load libthread_db: ");
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+ }
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/* This library "refused" to work on current inferior. */
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delete_thread_db_info (current_inferior ()->process_target (),
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@@ -1184,10 +1193,15 @@ has_libpthread (void)
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static bool
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thread_db_load (void)
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{
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- struct thread_db_info *info;
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+ inferior *inf = current_inferior ();
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- info = get_thread_db_info (current_inferior ()->process_target (),
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- inferior_ptid.pid ());
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+ /* When attaching / handling fork child, don't try loading libthread_db
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+ until we know about all shared libraries. */
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+ if (inf->in_initial_library_scan)
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+ return false;
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+
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+ thread_db_info *info = get_thread_db_info (inf->process_target (),
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+ inferior_ptid.pid ());
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if (info != NULL)
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return true;
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diff --git a/gdb/remote.c b/gdb/remote.c
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--- a/gdb/remote.c
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+++ b/gdb/remote.c
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@@ -14299,8 +14299,26 @@ remote_new_objfile (struct objfile *objfile)
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{
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remote_target *remote = get_current_remote_target ();
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- if (remote != NULL) /* Have a remote connection. */
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- remote->remote_check_symbols ();
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+ /* First, check whether the current inferior's process target is a remote
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+ target. */
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+ if (remote == nullptr)
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+ return;
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+
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+ /* When we are attaching or handling a fork child and the shared library
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+ subsystem reads the list of loaded libraries, we receive new objfile
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+ events in between each found library. The libraries are read in an
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+ undefined order, so if we gave the remote side a chance to look up
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+ symbols between each objfile, we might give it an inconsistent picture
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+ of the inferior. It could appear that a library A appears loaded but
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+ a library B does not, even though library A requires library B. That
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+ would present a state that couldn't normally exist in the inferior.
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+
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+ So, skip these events, we'll give the remote a chance to look up symbols
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+ once all the loaded libraries and their symbols are known to GDB. */
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+ if (current_inferior ()->in_initial_library_scan)
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+ return;
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+
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+ remote->remote_check_symbols ();
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}
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/* Pull all the tracepoints defined on the target and create local
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