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GDB upstream code reviews #40

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palmer-dabbelt opened this issue Dec 14, 2016 · 1 comment
Closed

GDB upstream code reviews #40

palmer-dabbelt opened this issue Dec 14, 2016 · 1 comment

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@palmer-dabbelt
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I believe this is the latest code review. I'm putting it here so it doesn't get lost

http://www.cygwin.com/ml/gdb-patches/2016-11/msg00461.html
@palmer-dabbelt
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I sent a v3: https://sourceware.org/ml/gdb-patches/2017-03/msg00047.html

@palmer-dabbelt palmer-dabbelt mentioned this issue May 1, 2017
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timsifive pushed a commit that referenced this issue Jul 3, 2018
@T-J-Teru
gdb: Remove cleanup from dw2_do_instantiate_symtab
b303c6f 
When running the test gdb.dwarf2/dw2-bad-parameter-type.exp under
valgrind, I see the following issue reported (on x86-64 Fedora):

  (gdb) ptype f
  ==5203== Invalid read of size 1
  ==5203==    at 0x6931FE: process_die_scope::~process_die_scope() (dwarf2read.c:10642)
  ==5203==    by 0x66818F: process_die(die_info*, dwarf2_cu*) (dwarf2read.c:10664)
  ==5203==    by 0x66A01F: read_file_scope(die_info*, dwarf2_cu*) (dwarf2read.c:11650)
  ==5203==    by 0x667F2D: process_die(die_info*, dwarf2_cu*) (dwarf2read.c:10672)
  ==5203==    by 0x6677B6: process_full_comp_unit(dwarf2_per_cu_data*, language) (dwarf2read.c:10445)
  ==5203==    by 0x66657A: process_queue(dwarf2_per_objfile*) (dwarf2read.c:9945)
  ==5203==    by 0x6559B4: dw2_do_instantiate_symtab(dwarf2_per_cu_data*) (dwarf2read.c:3163)
  ==5203==    by 0x66683D: psymtab_to_symtab_1(partial_symtab*) (dwarf2read.c:10034)
  ==5203==    by 0x66622A: dwarf2_read_symtab(partial_symtab*, objfile*) (dwarf2read.c:9811)
  ==5203==    by 0x787984: psymtab_to_symtab(objfile*, partial_symtab*) (psymtab.c:792)
  ==5203==    by 0x786E3E: psym_lookup_symbol(objfile*, int, char const*, domain_enum_tag) (psymtab.c:522)
  ==5203==    by 0x804BD0: lookup_symbol_via_quick_fns(objfile*, int, char const*, domain_enum_tag) (symtab.c:2383)
  ==5203==  Address 0x147ed063 is 291 bytes inside a block of size 4,064 free'd
  ==5203==    at 0x4C2CD5A: free (vg_replace_malloc.c:530)
  ==5203==    by 0x444415: void xfree<void>(void*) (common-utils.h:60)
  ==5203==    by 0x9DA8C2: call_freefun (obstack.c:103)
  ==5203==    by 0x9DAD35: _obstack_free (obstack.c:280)
  ==5203==    by 0x44464C: auto_obstack::~auto_obstack() (gdb_obstack.h:73)
  ==5203==    by 0x68AFB0: dwarf2_cu::~dwarf2_cu() (dwarf2read.c:25080)
  ==5203==    by 0x68B204: free_one_cached_comp_unit(dwarf2_per_cu_data*) (dwarf2read.c:25174)
  ==5203==    by 0x66668C: dwarf2_release_queue(void*) (dwarf2read.c:9982)
  ==5203==    by 0x563A4C: do_my_cleanups(cleanup**, cleanup*) (cleanups.c:154)
  ==5203==    by 0x563AA7: do_cleanups(cleanup*) (cleanups.c:176)
  ==5203==    by 0x5646CE: throw_exception_cxx(gdb_exception) (common-exceptions.c:289)
  ==5203==    by 0x5647B7: throw_exception(gdb_exception) (common-exceptions.c:317)
  ==5203==  Block was alloc'd at
  ==5203==    at 0x4C2BBAD: malloc (vg_replace_malloc.c:299)
  ==5203==    by 0x564BE8: xmalloc (common-utils.c:44)
  ==5203==    by 0x9DA872: call_chunkfun (obstack.c:94)
  ==5203==    by 0x9DA935: _obstack_begin_worker (obstack.c:141)
  ==5203==    by 0x9DAA3C: _obstack_begin (obstack.c:164)
  ==5203==    by 0x4445E0: auto_obstack::auto_obstack() (gdb_obstack.h:70)
  ==5203==    by 0x68AE07: dwarf2_cu::dwarf2_cu(dwarf2_per_cu_data*) (dwarf2read.c:25073)
  ==5203==    by 0x661A8A: init_cutu_and_read_dies(dwarf2_per_cu_data*, abbrev_table*, int, int, void (*)(die_reader_specs const*, unsigned char const*, die_info*, int, void*), void*) (dwarf2read.c:7869)
  ==5203==    by 0x666A29: load_full_comp_unit(dwarf2_per_cu_data*, language) (dwarf2read.c:10108)
  ==5203==    by 0x655847: load_cu(dwarf2_per_cu_data*) (dwarf2read.c:3120)
  ==5203==    by 0x655928: dw2_do_instantiate_symtab(dwarf2_per_cu_data*) (dwarf2read.c:3148)
  ==5203==    by 0x66683D: psymtab_to_symtab_1(partial_symtab*) (dwarf2read.c:10034)

There's actually a series of three issues reported, but it turns out
they're all related, so we can consider on the first one.

The invalid read is triggered from a destructor which is being invoked
as part of a stack unwind after throwing an error.  At the time the
error is thrown, the stack looks like this:

    #0  0x00000000009f4ecd in __cxa_throw ()
    #1  0x0000000000564761 in throw_exception_cxx (exception=...) at ../../src/gdb/common/common-exceptions.c:303
    #2  0x00000000005647b8 in throw_exception (exception=...) at ../../src/gdb/common/common-exceptions.c:317
    #3  0x00000000005648ff in throw_it(return_reason, errors, const char *, typedef __va_list_tag __va_list_tag *) (reason=RETURN_ERROR,
        error=GENERIC_ERROR, fmt=0xb33020 "Dwarf Error: Cannot find DIE at 0x%x referenced from DIE at 0x%x [in module %s]",
        ap=0x7fff387f2d68) at ../../src/gdb/common/common-exceptions.c:373
    #4  0x0000000000564929 in throw_verror (error=GENERIC_ERROR,
        fmt=0xb33020 "Dwarf Error: Cannot find DIE at 0x%x referenced from DIE at 0x%x [in module %s]", ap=0x7fff387f2d68)
        at ../../src/gdb/common/common-exceptions.c:379
    #5  0x0000000000867be4 in verror (string=0xb33020 "Dwarf Error: Cannot find DIE at 0x%x referenced from DIE at 0x%x [in module %s]",
        args=0x7fff387f2d68) at ../../src/gdb/utils.c:251
    #6  0x000000000056879d in error (fmt=0xb33020 "Dwarf Error: Cannot find DIE at 0x%x referenced from DIE at 0x%x [in module %s]")
        at ../../src/gdb/common/errors.c:43
    #7  0x0000000000686875 in follow_die_ref (src_die=0x30bc8a0, attr=0x30bc8c8, ref_cu=0x7fff387f2ed0) at ../../src/gdb/dwarf2read.c:22969
    #8  0x00000000006844cd in lookup_die_type (die=0x30bc8a0, attr=0x30bc8c8, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:21976
    #9  0x0000000000683f27 in die_type (die=0x30bc8a0, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:21832
    #10 0x0000000000679b39 in read_subroutine_type (die=0x30bc830, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:17343
    #11 0x00000000006845fb in read_type_die_1 (die=0x30bc830, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:22035
    #12 0x0000000000684576 in read_type_die (die=0x30bc830, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:22010
    #13 0x000000000067003f in read_func_scope (die=0x30bc830, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:13822
    #14 0x0000000000667f5e in process_die (die=0x30bc830, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:10679
    #15 0x000000000066a020 in read_file_scope (die=0x30bc720, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:11650
    #16 0x0000000000667f2e in process_die (die=0x30bc720, cu=0x30bc5d0) at ../../src/gdb/dwarf2read.c:10672
    #17 0x00000000006677b7 in process_full_comp_unit (per_cu=0x3089b80, pretend_language=language_minimal)
        at ../../src/gdb/dwarf2read.c:10445
    #18 0x000000000066657b in process_queue (dwarf2_per_objfile=0x30897d0) at ../../src/gdb/dwarf2read.c:9945
    #19 0x00000000006559b5 in dw2_do_instantiate_symtab (per_cu=0x3089b80) at ../../src/gdb/dwarf2read.c:3163
    #20 0x000000000066683e in psymtab_to_symtab_1 (pst=0x3089bd0) at ../../src/gdb/dwarf2read.c:10034
    #21 0x000000000066622b in dwarf2_read_symtab (self=0x3089bd0, objfile=0x3073f40) at ../../src/gdb/dwarf2read.c:9811
    #22 0x0000000000787985 in psymtab_to_symtab (objfile=0x3073f40, pst=0x3089bd0) at ../../src/gdb/psymtab.c:792
    #23 0x0000000000786e3f in psym_lookup_symbol (objfile=0x3073f40, block_index=1, name=0x30b2e30 "f", domain=VAR_DOMAIN)
        at ../../src/gdb/psymtab.c:522
    #24 0x0000000000804bd1 in lookup_symbol_via_quick_fns (objfile=0x3073f40, block_index=1, name=0x30b2e30 "f", domain=VAR_DOMAIN)
        at ../../src/gdb/symtab.c:2383
    #25 0x0000000000804fe4 in lookup_symbol_in_objfile (objfile=0x3073f40, block_index=1, name=0x30b2e30 "f", domain=VAR_DOMAIN)
        at ../../src/gdb/symtab.c:2558
    #26 0x0000000000805125 in lookup_static_symbol (name=0x30b2e30 "f", domain=VAR_DOMAIN) at ../../src/gdb/symtab.c:2595
    #27 0x0000000000804357 in lookup_symbol_aux (name=0x30b2e30 "f", match_type=symbol_name_match_type::FULL, block=0x0,
        domain=VAR_DOMAIN, language=language_c, is_a_field_of_this=0x0) at ../../src/gdb/symtab.c:2105
    #28 0x0000000000803ad9 in lookup_symbol_in_language (name=0x30b2e30 "f", block=0x0, domain=VAR_DOMAIN, lang=language_c,
        is_a_field_of_this=0x0) at ../../src/gdb/symtab.c:1887
    #29 0x0000000000803b53 in lookup_symbol (name=0x30b2e30 "f", block=0x0, domain=VAR_DOMAIN, is_a_field_of_this=0x0)
        at ../../src/gdb/symtab.c:1899
    #30 0x000000000053b246 in classify_name (par_state=0x7fff387f6090, block=0x0, is_quoted_name=false, is_after_structop=false)
        at ../../src/gdb/c-exp.y:2879
    #31 0x000000000053b7e9 in c_yylex () at ../../src/gdb/c-exp.y:3083
    #32 0x000000000053414a in c_yyparse () at c-exp.c:1903
    #33 0x000000000053c2e7 in c_parse (par_state=0x7fff387f6090) at ../../src/gdb/c-exp.y:3255
    #34 0x0000000000774a02 in parse_exp_in_context_1 (stringptr=0x7fff387f61c0, pc=0, block=0x0, comma=0, void_context_p=0, out_subexp=0x0)
        at ../../src/gdb/parse.c:1213
    #35 0x000000000077476a in parse_exp_in_context (stringptr=0x7fff387f61c0, pc=0, block=0x0, comma=0, void_context_p=0, out_subexp=0x0)
        at ../../src/gdb/parse.c:1115
    #36 0x0000000000774714 in parse_exp_1 (stringptr=0x7fff387f61c0, pc=0, block=0x0, comma=0) at ../../src/gdb/parse.c:1106
    #37 0x0000000000774c53 in parse_expression (string=0x27ff996 "f") at ../../src/gdb/parse.c:1253
    #38 0x0000000000861dc4 in whatis_exp (exp=0x27ff996 "f", show=1) at ../../src/gdb/typeprint.c:472
    #39 0x00000000008620d8 in ptype_command (type_name=0x27ff996 "f", from_tty=1) at ../../src/gdb/typeprint.c:561
    #40 0x000000000047430b in do_const_cfunc (c=0x3012010, args=0x27ff996 "f", from_tty=1) at ../../src/gdb/cli/cli-decode.c:106
    #41 0x000000000047715e in cmd_func (cmd=0x3012010, args=0x27ff996 "f", from_tty=1) at ../../src/gdb/cli/cli-decode.c:1886
    #42 0x00000000008431bb in execute_command (p=0x27ff996 "f", from_tty=1) at ../../src/gdb/top.c:630
    #43 0x00000000006bf946 in command_handler (command=0x27ff990 "ptype f") at ../../src/gdb/event-top.c:583
    #44 0x00000000006bfd12 in command_line_handler (rl=0x30bb3a0 "\240\305\v\003") at ../../src/gdb/event-top.c:774

The problem is that in `process_die` (frames 14 and 16) we create a
`process_die_scope` object, that takes a copy of the `struct
dwarf2_cu *` passed into the frame.  The destructor of the
`process_die_scope` dereferences the stored pointer.  This wouldn't be
an issue, except...

... in dw2_do_instantiate_symtab (frame 19) a clean up was registered that
clears the dwarf2_queue in case of an error.  Part of this clean up
involves deleting the `struct dwarf2_cu`s referenced from the queue..

The problem then, is that cleanups are processed at the site of the
throw, while, class destructors are invoked as we unwind their frame.
The result is that we process the frame 19 cleanup (and delete the
struct dwarf2_cu) before we process the destructors in frames 14 and 16.
When we do get back to frames 14 and 16 the objects being references
have already been deleted.

The solution is to remove the cleanup from dw2_do_instantiate_symtab, and
instead use a destructor to release the dwarf2_queue instead.  With this
patch in place, the valgrind errors are now resolved.

gdb/ChangeLog:

	* dwarf2read.c (dwarf2_release_queue): Delete function, move body
	into...
	(class dwarf2_queue_guard): ...the destructor of this new class.
	(dw2_do_instantiate_symtab): Create instance of the new class
	dwarf2_queue_guard, remove cleanup.
Nelson1225 pushed a commit to Nelson1225/riscv-binutils-gdb that referenced this issue Jun 15, 2021
@simark
gdb: try to load libthread_db only after reading all shared libraries…
122373f 
… when attaching / handling a fork child

When trying to attach to a pthread process on a Linux system with glibc 2.33,
we get:

    $ ./gdb -q -nx --data-directory=data-directory -p 1472010
    Attaching to process 1472010
    [New LWP 1472013]
    [New LWP 1472014]
    [New LWP 1472015]
    Error while reading shared library symbols for /usr/lib/libpthread.so.0:
    Cannot find user-level thread for LWP 1472015: generic error
    0x00007ffff6d3637f in poll () from /usr/lib/libc.so.6
    (gdb)

When attaching to a process (or handling a fork child, an operation very
similar to attaching), GDB reads the shared library list from the
process.  For each shared library (if "set auto-solib-add" is on), it
reads its symbols and calls the "new_objfile" observable.

The libthread-db code monitors this observable, and if it sees an
objfile named somewhat like "libpthread.so" go by, it tries to load
libthread_db.so in the GDB process itself.  libthread_db knows how to
navigate libpthread's data structures to get information about the
existing threads.

To locate these data structures, libthread_db calls ps_pglobal_lookup
(implemented in proc-service.c), passing in a symbol name and expecting
an address in return.

Before glibc 2.33, libthread_db always asked for symbols found in
libpthread.  There was no ordering problem: since we were always trying
to load libthread_db in reaction to processing libpthread (and reading
in its symbols) and libthread_db only asked symbols from libpthread, the
requested symbols could always be found.  Starting with glibc 2.33,
libthread_db now asks for a symbol name that can be found in
/lib/ld-linux-x86-64.so.2 (_rtld_global).  And the ordering in which GDB
reads the shared libraries from the inferior when attaching is
unfortunate, in that libpthread is processed before ld-linux.  So when
loading libthread_db in reaction to processing libpthread, and
libthread_db requests the symbol that is from ld-linux, GDB is not yet
able to supply it.

That problematic symbol lookup happens in the thread_from_lwp function,
when we call td_ta_map_lwp2thr_p, and an exception is thrown at this
point:

    #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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#5  0x000055555d06b4bc in thread_from_lwp (stopped=0x617000035d80, ptid=...) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:418
    riscvarchive#6  0x000055555d07040d in try_thread_db_load_1 (info=0x60c000011140) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:912
    riscvarchive#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
    riscvarchive#8  0x000055555d072168 in try_thread_db_load_from_sdir () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1091
    riscvarchive#9  0x000055555d072d1c in thread_db_load_search () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1146
    riscvarchive#10 0x000055555d07365c in thread_db_load () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1203
    riscvarchive#11 0x000055555d07373e in check_for_thread_db () at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1246
    riscvarchive#12 0x000055555d0738ab in thread_db_new_objfile (objfile=0x61300000c0c0) at /home/simark/src/binutils-gdb/gdb/linux-thread-db.c:1275
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#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
    riscvarchive#20 0x000055555d95f9fa in solib_read_symbols (so=0x6190000d8e80, flags=...) at /home/simark/src/binutils-gdb/gdb/solib.c:681
    riscvarchive#21 0x000055555d96233d in solib_add (pattern=0x0, from_tty=0, readsyms=1) at /home/simark/src/binutils-gdb/gdb/solib.c:987
    riscvarchive#22 0x000055555d93646e in enable_break (info=0x608000008f20, from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2238
    riscvarchive#23 0x000055555d93cfc0 in svr4_solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:3049
    riscvarchive#24 0x000055555d96610d in solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib.c:1195
    riscvarchive#25 0x000055555cdee318 in post_create_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:318
    riscvarchive#26 0x000055555ce00e6e in setup_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:2439
    riscvarchive#27 0x000055555ce59c34 in handle_one (event=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:4887
    riscvarchive#28 0x000055555ce5cd00 in stop_all_threads () at /home/simark/src/binutils-gdb/gdb/infrun.c:5064
    riscvarchive#29 0x000055555ce7f0da in stop_waiting (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:8006
    riscvarchive#30 0x000055555ce67f5c in handle_signal_stop (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:6062
    riscvarchive#31 0x000055555ce63653 in handle_inferior_event (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:5727
    riscvarchive#32 0x000055555ce4f297 in fetch_inferior_event () at /home/simark/src/binutils-gdb/gdb/infrun.c:4105
    riscvarchive#33 0x000055555cdbe3bf in inferior_event_handler (event_type=INF_REG_EVENT) at /home/simark/src/binutils-gdb/gdb/inf-loop.c:42
    riscvarchive#34 0x000055555d018047 in handle_target_event (error=0, client_data=0x0) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:4060
    riscvarchive#35 0x000055555e5ea77e in handle_file_event (file_ptr=0x60600008b1c0, ready_mask=1) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:575
    riscvarchive#36 0x000055555e5eb09c in gdb_wait_for_event (block=0) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:701
    riscvarchive#37 0x000055555e5e8d19 in gdb_do_one_event () at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:212
    riscvarchive#38 0x000055555dd6e0d4 in wait_sync_command_done () at /home/simark/src/binutils-gdb/gdb/top.c:528
    riscvarchive#39 0x000055555dd6e372 in maybe_wait_sync_command_done (was_sync=0) at /home/simark/src/binutils-gdb/gdb/top.c:545
    riscvarchive#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
    riscvarchive#41 0x000055555d0f03ad in captured_main_1 (context=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1149
    riscvarchive#42 0x000055555d0f1239 in captured_main (data=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1232
    riscvarchive#43 0x000055555d0f1315 in gdb_main (args=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1257
    riscvarchive#44 0x000055555bb70cf9 in main (argc=7, argv=0x7fffffffde88) at /home/simark/src/binutils-gdb/gdb/gdb.c:32

The exception is caught here:

    #0  __cxxabiv1::__cxa_begin_catch (exc_obj_in=0x60e0000060e0) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_catch.cc:84
    riscvarchive#1  0x000055555d95fded in solib_read_symbols (so=0x6190000d8e80, flags=...) at /home/simark/src/binutils-gdb/gdb/solib.c:689
    riscvarchive#2  0x000055555d96233d in solib_add (pattern=0x0, from_tty=0, readsyms=1) at /home/simark/src/binutils-gdb/gdb/solib.c:987
    riscvarchive#3  0x000055555d93646e in enable_break (info=0x608000008f20, from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:2238
    riscvarchive#4  0x000055555d93cfc0 in svr4_solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib-svr4.c:3049
    riscvarchive#5  0x000055555d96610d in solib_create_inferior_hook (from_tty=0) at /home/simark/src/binutils-gdb/gdb/solib.c:1195
    riscvarchive#6  0x000055555cdee318 in post_create_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:318
    riscvarchive#7  0x000055555ce00e6e in setup_inferior (from_tty=0) at /home/simark/src/binutils-gdb/gdb/infcmd.c:2439
    riscvarchive#8  0x000055555ce59c34 in handle_one (event=...) at /home/simark/src/binutils-gdb/gdb/infrun.c:4887
    riscvarchive#9  0x000055555ce5cd00 in stop_all_threads () at /home/simark/src/binutils-gdb/gdb/infrun.c:5064
    riscvarchive#10 0x000055555ce7f0da in stop_waiting (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:8006
    riscvarchive#11 0x000055555ce67f5c in handle_signal_stop (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:6062
    riscvarchive#12 0x000055555ce63653 in handle_inferior_event (ecs=0x7fffffffd170) at /home/simark/src/binutils-gdb/gdb/infrun.c:5727
    riscvarchive#13 0x000055555ce4f297 in fetch_inferior_event () at /home/simark/src/binutils-gdb/gdb/infrun.c:4105
    riscvarchive#14 0x000055555cdbe3bf in inferior_event_handler (event_type=INF_REG_EVENT) at /home/simark/src/binutils-gdb/gdb/inf-loop.c:42
    riscvarchive#15 0x000055555d018047 in handle_target_event (error=0, client_data=0x0) at /home/simark/src/binutils-gdb/gdb/linux-nat.c:4060
    riscvarchive#16 0x000055555e5ea77e in handle_file_event (file_ptr=0x60600008b1c0, ready_mask=1) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:575
    riscvarchive#17 0x000055555e5eb09c in gdb_wait_for_event (block=0) at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:701
    riscvarchive#18 0x000055555e5e8d19 in gdb_do_one_event () at /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:212
    riscvarchive#19 0x000055555dd6e0d4 in wait_sync_command_done () at /home/simark/src/binutils-gdb/gdb/top.c:528
    riscvarchive#20 0x000055555dd6e372 in maybe_wait_sync_command_done (was_sync=0) at /home/simark/src/binutils-gdb/gdb/top.c:545
    riscvarchive#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
    riscvarchive#22 0x000055555d0f03ad in captured_main_1 (context=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1149
    riscvarchive#23 0x000055555d0f1239 in captured_main (data=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1232
    riscvarchive#24 0x000055555d0f1315 in gdb_main (args=0x7fffffffdd10) at /home/simark/src/binutils-gdb/gdb/main.c:1257
    riscvarchive#25 0x000055555bb70cf9 in main (argc=7, argv=0x7fffffffde88) at /home/simark/src/binutils-gdb/gdb/gdb.c:32

Catching the exception at this point means that the thread_db_info
object for this inferior will be left in place, despite the failure to
load libthread_db.  This means that there won't be further attempts at
loading libthread_db, because thread_db_load will think that
libthread_db is already loaded for this inferior and will always exit
early.  To fix this, add a try/catch around calling try_thread_db_load_1
in try_thread_db_load, such that if some exception is thrown while
trying to load libthread_db, we reset / delete the thread_db_info for
that inferior.  That alone makes attach work fine again, because
check_for_thread_db is called again in the thread_db_inferior_created
observer (that happens after we learned about all shared libraries and
their symbols), and libthread_db is successfully loaded then.

When attaching, I think that the inferior_created observer is a good
place to try to load libthread_db: it is called once everything has
stabilized, when we learned about all shared libraries.

The only problem then is that when we first try (and fail) to load
libthread_db, in reaction to learning about libpthread, we show this
warning:

    warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.

This is misleading, because we do succeed in loading it later.  So when
attaching, I think we shouldn't try to load libthread_db in reaction to
the new_objfile events, we should wait until we have learned about all
shared libraries (using the inferior_created observable).  To do so, add
an `in_initial_library_scan` flag to struct inferior.  This flag is used
to postpone loading libthread_db if we are attaching or handling a fork
child.

When debugging remotely with GDBserver, the same problem happens, except
that the qSymbol mechanism (allowing the remote side to ask GDB for
symbols values) is involved.  The fix there is the same idea, we make
GDB wait until all shared libraries and their symbols are known before
sending out a qSymbol packet.  This way, we never present the remote
side a state where libpthread.so's symbols are known but ld-linux's
symbols aren't.

gdb/ChangeLog:

	* inferior.h (class inferior) <in_initial_library_scan>: New.
	* infcmd.c (post_create_inferior): Set in_initial_library_scan.
	* infrun.c (follow_fork_inferior): Likewise.
	* linux-thread-db.c (try_thread_db_load): Catch exception thrown
	by try_thread_db_load_1
	(thread_db_load): Return early if in_initial_library_scan is
	set.
	* remote.c (remote_new_objfile): Return early if
	in_initial_library_scan is set.

Change-Id: I7a279836cfbb2b362b4fde11b196b4aab82f5efb
Nelson1225 pushed a commit to Nelson1225/riscv-binutils-gdb that referenced this issue Jul 22, 2021
@simark
gdb: set current thread in btrace_compute_ftrace_{bts,pt}
ecd799b 
As documented in bug 28086, test gdb.btrace/enable-new-thread.exp
started failing with commit 0618ae4 ("gdb: optimize
all_matching_threads_iterator"):

    (gdb) record btrace^M
    (gdb) PASS: gdb.btrace/enable-new-thread.exp: record btrace
    break 24^M
    Breakpoint 2 at 0x555555555175: file /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.btrace/enable-new-thread.c, line 24.^M
    (gdb) continue^M
    Continuing.^M
    /home/smarchi/src/binutils-gdb/gdb/inferior.c:303: internal-error: inferior* find_inferior_pid(process_stratum_target*, int): Assertion `pid != 0' failed.^M
    A problem internal to GDB has been detected,^M
    further debugging may prove unreliable.^M
    Quit this debugging session? (y or n) FAIL: gdb.btrace/enable-new-thread.exp: continue to breakpoint: cont to bp.1 (GDB internal error)

Note that I only see the failure if GDB is compiled without libipt
support.  This is because GDB then makes use BTS instead of PT, so
exercises different code paths.

I think that the commit above just exposed an existing problem.  The
stack trace of the internal error is:

    riscvarchive#8  0x0000561cb81e404e in internal_error (file=0x561cb83aa2f8 "/home/smarchi/src/binutils-gdb/gdb/inferior.c", line=303, fmt=0x561cb83aa099 "%s: Assertion `%s' failed.") at /home/smarchi/src/binutils-gdb/gdbsupport/errors.cc:55
    riscvarchive#9  0x0000561cb7b5c031 in find_inferior_pid (targ=0x561cb8aafb60 <the_amd64_linux_nat_target>, pid=0) at /home/smarchi/src/binutils-gdb/gdb/inferior.c:303
    riscvarchive#10 0x0000561cb7b5c102 in find_inferior_ptid (targ=0x561cb8aafb60 <the_amd64_linux_nat_target>, ptid=...) at /home/smarchi/src/binutils-gdb/gdb/inferior.c:317
    riscvarchive#11 0x0000561cb7f1d1c3 in find_thread_ptid (targ=0x561cb8aafb60 <the_amd64_linux_nat_target>, ptid=...) at /home/smarchi/src/binutils-gdb/gdb/thread.c:487
    riscvarchive#12 0x0000561cb7f1b921 in all_matching_threads_iterator::all_matching_threads_iterator (this=0x7ffc4ee34678, filter_target=0x561cb8aafb60 <the_amd64_linux_nat_target>, filter_ptid=...) at /home/smarchi/src/binutils-gdb/gdb/thread-iter.c:125
    riscvarchive#13 0x0000561cb77bc462 in filtered_iterator<all_matching_threads_iterator, non_exited_thread_filter>::filtered_iterator<process_stratum_target* const&, ptid_t const&> (this=0x7ffc4ee34670) at /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/filtered-iterator.h:42
    riscvarchive#14 0x0000561cb77b97cb in all_non_exited_threads_range::begin (this=0x7ffc4ee34650) at /home/smarchi/src/binutils-gdb/gdb/thread-iter.h:243
    riscvarchive#15 0x0000561cb7d8ba30 in record_btrace_target::record_is_replaying (this=0x561cb8aa6250 <record_btrace_ops>, ptid=...) at /home/smarchi/src/binutils-gdb/gdb/record-btrace.c:1411
    riscvarchive#16 0x0000561cb7d8bb83 in record_btrace_target::xfer_partial (this=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_MEMORY, annex=0x0, readbuf=0x7ffc4ee34c58 "\260g\343N\374\177", writebuf=0x0, offset=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/record-btrace.c:1437
    riscvarchive#17 0x0000561cb7ef73a9 in raw_memory_xfer_partial (ops=0x561cb8aa6250 <record_btrace_ops>, readbuf=0x7ffc4ee34c58 "\260g\343N\374\177", writebuf=0x0, memaddr=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/target.c:1504
    riscvarchive#18 0x0000561cb7ef77da in memory_xfer_partial_1 (ops=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_CODE_MEMORY, readbuf=0x7ffc4ee34c58 "\260g\343N\374\177", writebuf=0x0, memaddr=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/target.c:1635
    riscvarchive#19 0x0000561cb7ef78b5 in memory_xfer_partial (ops=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_CODE_MEMORY, readbuf=0x7ffc4ee34c58 "\260g\343N\374\177", writebuf=0x0, memaddr=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/target.c:1664
    riscvarchive#20 0x0000561cb7ef7ba4 in target_xfer_partial (ops=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_CODE_MEMORY, annex=0x0, readbuf=0x7ffc4ee34c58 "\260g\343N\374\177", writebuf=0x0, offset=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/target.c:1721
    riscvarchive#21 0x0000561cb7ef8503 in target_read_partial (ops=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_CODE_MEMORY, annex=0x0, buf=0x7ffc4ee34c58 "\260g\343N\374\177", offset=140737352774277, len=1, xfered_len=0x7ffc4ee34ad8) at /home/smarchi/src/binutils-gdb/gdb/target.c:1974
    riscvarchive#22 0x0000561cb7ef861f in target_read (ops=0x561cb8aa6250 <record_btrace_ops>, object=TARGET_OBJECT_CODE_MEMORY, annex=0x0, buf=0x7ffc4ee34c58 "\260g\343N\374\177", offset=140737352774277, len=1) at /home/smarchi/src/binutils-gdb/gdb/target.c:2014
    riscvarchive#23 0x0000561cb7ef809f in target_read_code (memaddr=140737352774277, myaddr=0x7ffc4ee34c58 "\260g\343N\374\177", len=1) at /home/smarchi/src/binutils-gdb/gdb/target.c:1869
    riscvarchive#24 0x0000561cb7937f4d in gdb_disassembler::dis_asm_read_memory (memaddr=140737352774277, myaddr=0x7ffc4ee34c58 "\260g\343N\374\177", len=1, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/gdb/disasm.c:139
    riscvarchive#25 0x0000561cb80ab66d in fetch_data (info=0x7ffc4ee34e88, addr=0x7ffc4ee34c59 "g\343N\374\177") at /home/smarchi/src/binutils-gdb/opcodes/i386-dis.c:194
    riscvarchive#26 0x0000561cb80ab7e2 in ckprefix () at /home/smarchi/src/binutils-gdb/opcodes/i386-dis.c:8628
    riscvarchive#27 0x0000561cb80adbd8 in print_insn (pc=140737352774277, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/opcodes/i386-dis.c:9587
    riscvarchive#28 0x0000561cb80abe4f in print_insn_i386 (pc=140737352774277, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/opcodes/i386-dis.c:8894
    riscvarchive#29 0x0000561cb7744a19 in default_print_insn (memaddr=140737352774277, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/gdb/arch-utils.c:1029
    riscvarchive#30 0x0000561cb7b33067 in i386_print_insn (pc=140737352774277, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/gdb/i386-tdep.c:4013
    riscvarchive#31 0x0000561cb7acd8f4 in gdbarch_print_insn (gdbarch=0x561cbae2fb60, vma=140737352774277, info=0x7ffc4ee34e88) at /home/smarchi/src/binutils-gdb/gdb/gdbarch.c:3478
    riscvarchive#32 0x0000561cb793a32d in gdb_disassembler::print_insn (this=0x7ffc4ee34e80, memaddr=140737352774277, branch_delay_insns=0x0) at /home/smarchi/src/binutils-gdb/gdb/disasm.c:795
    riscvarchive#33 0x0000561cb793a5b0 in gdb_print_insn (gdbarch=0x561cbae2fb60, memaddr=140737352774277, stream=0x561cb8ac99f8 <null_stream>, branch_delay_insns=0x0) at /home/smarchi/src/binutils-gdb/gdb/disasm.c:850
    riscvarchive#34 0x0000561cb793a631 in gdb_insn_length (gdbarch=0x561cbae2fb60, addr=140737352774277) at /home/smarchi/src/binutils-gdb/gdb/disasm.c:859
    riscvarchive#35 0x0000561cb77f53f4 in btrace_compute_ftrace_bts (tp=0x561cbba11210, btrace=0x7ffc4ee35188, gaps=...) at /home/smarchi/src/binutils-gdb/gdb/btrace.c:1107
    riscvarchive#36 0x0000561cb77f55f5 in btrace_compute_ftrace_1 (tp=0x561cbba11210, btrace=0x7ffc4ee35180, cpu=0x0, gaps=...) at /home/smarchi/src/binutils-gdb/gdb/btrace.c:1527
    riscvarchive#37 0x0000561cb77f5705 in btrace_compute_ftrace (tp=0x561cbba11210, btrace=0x7ffc4ee35180, cpu=0x0) at /home/smarchi/src/binutils-gdb/gdb/btrace.c:1560
    riscvarchive#38 0x0000561cb77f583b in btrace_add_pc (tp=0x561cbba11210) at /home/smarchi/src/binutils-gdb/gdb/btrace.c:1589
    riscvarchive#39 0x0000561cb77f5a86 in btrace_enable (tp=0x561cbba11210, conf=0x561cb8ac6878 <record_btrace_conf>) at /home/smarchi/src/binutils-gdb/gdb/btrace.c:1629
    riscvarchive#40 0x0000561cb7d88d26 in record_btrace_enable_warn (tp=0x561cbba11210) at /home/smarchi/src/binutils-gdb/gdb/record-btrace.c:294
    riscvarchive#41 0x0000561cb7c603dc in std::__invoke_impl<void, void (*&)(thread_info*), thread_info*> (__f=@0x561cbb6c4878: 0x561cb7d88cdc <record_btrace_enable_warn(thread_info*)>) at /usr/include/c++/10/bits/invoke.h:60
    riscvarchive#42 0x0000561cb7c5e5a6 in std::__invoke_r<void, void (*&)(thread_info*), thread_info*> (__fn=@0x561cbb6c4878: 0x561cb7d88cdc <record_btrace_enable_warn(thread_info*)>) at /usr/include/c++/10/bits/invoke.h:153
    riscvarchive#43 0x0000561cb7c5dc92 in std::_Function_handler<void (thread_info*), void (*)(thread_info*)>::_M_invoke(std::_Any_data const&, thread_info*&&) (__functor=..., __args#0=@0x7ffc4ee35310: 0x561cbba11210) at /usr/include/c++/10/bits/std_function.h:291
    riscvarchive#44 0x0000561cb7f2600f in std::function<void (thread_info*)>::operator()(thread_info*) const (this=0x561cbb6c4878, __args#0=0x561cbba11210) at /usr/include/c++/10/bits/std_function.h:622
    riscvarchive#45 0x0000561cb7f23dc8 in gdb::observers::observable<thread_info*>::notify (this=0x561cb8ac5aa0 <gdb::observers::new_thread>, args#0=0x561cbba11210) at /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/observable.h:150
    riscvarchive#46 0x0000561cb7f1c436 in add_thread_silent (targ=0x561cb8aafb60 <the_amd64_linux_nat_target>, ptid=...) at /home/smarchi/src/binutils-gdb/gdb/thread.c:263
    riscvarchive#47 0x0000561cb7f1c479 in add_thread_with_info (targ=0x561cb8aafb60 <the_amd64_linux_nat_target>, ptid=..., priv=0x561cbb3f7ab0) at /home/smarchi/src/binutils-gdb/gdb/thread.c:272
    riscvarchive#48 0x0000561cb7bfa1d0 in record_thread (info=0x561cbb0413a0, tp=0x0, ptid=..., th_p=0x7ffc4ee35610, ti_p=0x7ffc4ee35620) at /home/smarchi/src/binutils-gdb/gdb/linux-thread-db.c:1380
    riscvarchive#49 0x0000561cb7bf7a2a in thread_from_lwp (stopped=0x561cba81db20, ptid=...) at /home/smarchi/src/binutils-gdb/gdb/linux-thread-db.c:429
    riscvarchive#50 0x0000561cb7bf7ac5 in thread_db_notice_clone (parent=..., child=...) at /home/smarchi/src/binutils-gdb/gdb/linux-thread-db.c:447
    riscvarchive#51 0x0000561cb7bdc9a2 in linux_handle_extended_wait (lp=0x561cbae25720, status=4991) at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:1981
    riscvarchive#52 0x0000561cb7bdf0f3 in linux_nat_filter_event (lwpid=435403, status=198015) at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:2920
    riscvarchive#53 0x0000561cb7bdfed6 in linux_nat_wait_1 (ptid=..., ourstatus=0x7ffc4ee36398, target_options=...) at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:3202
    riscvarchive#54 0x0000561cb7be0b68 in linux_nat_target::wait (this=0x561cb8aafb60 <the_amd64_linux_nat_target>, ptid=..., ourstatus=0x7ffc4ee36398, target_options=...) at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:3440
    riscvarchive#55 0x0000561cb7bfa2fc in thread_db_target::wait (this=0x561cb8a9acd0 <the_thread_db_target>, ptid=..., ourstatus=0x7ffc4ee36398, options=...) at /home/smarchi/src/binutils-gdb/gdb/linux-thread-db.c:1412
    riscvarchive#56 0x0000561cb7d8e356 in record_btrace_target::wait (this=0x561cb8aa6250 <record_btrace_ops>, ptid=..., status=0x7ffc4ee36398, options=...) at /home/smarchi/src/binutils-gdb/gdb/record-btrace.c:2547
    riscvarchive#57 0x0000561cb7ef996d in target_wait (ptid=..., status=0x7ffc4ee36398, options=...) at /home/smarchi/src/binutils-gdb/gdb/target.c:2608
    riscvarchive#58 0x0000561cb7b6d297 in do_target_wait_1 (inf=0x561cba6d8780, ptid=..., status=0x7ffc4ee36398, options=...) at /home/smarchi/src/binutils-gdb/gdb/infrun.c:3640
    riscvarchive#59 0x0000561cb7b6d43e in operator() (__closure=0x7ffc4ee36190, inf=0x561cba6d8780) at /home/smarchi/src/binutils-gdb/gdb/infrun.c:3701
    riscvarchive#60 0x0000561cb7b6d7b2 in do_target_wait (ecs=0x7ffc4ee36370, options=...) at /home/smarchi/src/binutils-gdb/gdb/infrun.c:3720
    riscvarchive#61 0x0000561cb7b6e67d in fetch_inferior_event () at /home/smarchi/src/binutils-gdb/gdb/infrun.c:4069
    riscvarchive#62 0x0000561cb7b4659b in inferior_event_handler (event_type=INF_REG_EVENT) at /home/smarchi/src/binutils-gdb/gdb/inf-loop.c:41
    riscvarchive#63 0x0000561cb7be25f7 in handle_target_event (error=0, client_data=0x0) at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:4227
    riscvarchive#64 0x0000561cb81e4ee2 in handle_file_event (file_ptr=0x561cbae24e10, ready_mask=1) at /home/smarchi/src/binutils-gdb/gdbsupport/event-loop.cc:575
    riscvarchive#65 0x0000561cb81e5490 in gdb_wait_for_event (block=0) at /home/smarchi/src/binutils-gdb/gdbsupport/event-loop.cc:701
    riscvarchive#66 0x0000561cb81e41be in gdb_do_one_event () at /home/smarchi/src/binutils-gdb/gdbsupport/event-loop.cc:212
    riscvarchive#67 0x0000561cb7c18096 in start_event_loop () at /home/smarchi/src/binutils-gdb/gdb/main.c:421
    riscvarchive#68 0x0000561cb7c181e0 in captured_command_loop () at /home/smarchi/src/binutils-gdb/gdb/main.c:481
    riscvarchive#69 0x0000561cb7c19d7e in captured_main (data=0x7ffc4ee366a0) at /home/smarchi/src/binutils-gdb/gdb/main.c:1353
    riscvarchive#70 0x0000561cb7c19df0 in gdb_main (args=0x7ffc4ee366a0) at /home/smarchi/src/binutils-gdb/gdb/main.c:1368
    riscvarchive#71 0x0000561cb7693186 in main (argc=11, argv=0x7ffc4ee367b8) at /home/smarchi/src/binutils-gdb/gdb/gdb.c:32

At frame 45, the new_thread observable is fired.  At this moment, the
new thread isn't the current thread, inferior_ptid is null_ptid.  I
think this is ok: the new_thread observable doesn't give any guarantee
on the global context when observers are invoked.  Frame 35,
btrace_compute_ftrace_bts, calls gdb_insn_length.  gdb_insn_length
doesn't have a thread_info or other parameter what could indicate where
to read memory from, it implicitly uses the global context
(inferior_ptid).

So we reach the all_non_exited_threads_range in
record_btrace_target::record_is_replaying with a null inferior_ptid.
The previous implemention of all_non_exited_threads_range didn't care,
but the new one does.  The problem of calling gdb_insn_length and
ultimately trying to read memory with a null inferior_ptid already
existed, but the commit mentioned above made it visible.

Something between frames 40 (record_btrace_enable_warn) and 35
(btrace_compute_ftrace_bts) needs to be switching the global context to
make TP the current thread.  Since btrace_compute_ftrace_bts takes the
thread_info to work with as a parameter, that typically means that it
doesn't require its caller to also set the global current context
(current thread) when calling.  If it needs to call other functions
that do require the global current thread to be set, then it needs to
temporarily change the current thread while calling these other
functions.  Therefore, switch and restore the current thread in
btrace_compute_ftrace_bts.

By inspection, it looks like btrace_compute_ftrace_pt may also call
functions sensitive to the global context: it installs the
btrace_pt_readmem_callback callback in the PT instruction decoder.  When
this function gets called, inferior_ptid must be set appropriately.  Add
a switch and restore in there too.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28086
Change-Id: I407fbfe41aab990068bd102491aa3709b0a034b3
Nelson1225 pushed a commit that referenced this issue Feb 10, 2022
@simark
gdb: work around negative DW_AT_data_member_location GCC 11 bug
dfa1952 
g++ 11.1.0 has a bug where it will emit a negative
DW_AT_data_member_location in some cases:

    $ cat test.cpp
    #include <memory>

    int
    main()
    {
      std::unique_ptr<int> ptr;
    }
    $ g++ -g test.cpp
    $ llvm-dwarfdump -F a.out
    ...
    0x00000964:       DW_TAG_member
                        DW_AT_name [DW_FORM_strp]   ("_M_head_impl")
                        DW_AT_decl_file [DW_FORM_data1]     ("/usr/include/c++/11.1.0/tuple")
                        DW_AT_decl_line [DW_FORM_data1]     (125)
                        DW_AT_decl_column [DW_FORM_data1]   (0x27)
                        DW_AT_type [DW_FORM_ref4]   (0x0000067a "default_delete<int>")
                        DW_AT_data_member_location [DW_FORM_sdata]  (-1)
    ...

This leads to a GDB crash (when built with ASan, otherwise probably
garbage results), since it tries to read just before (to the left, in
ASan speak) of the value's buffer:

    ==888645==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6020000c52af at pc 0x7f711b239f4b bp 0x7fff356bd470 sp 0x7fff356bcc18
    READ of size 1 at 0x6020000c52af thread T0
        #0 0x7f711b239f4a in __interceptor_memcpy /build/gcc/src/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:827
        #1 0x555c4977efa1 in value_contents_copy_raw /home/simark/src/binutils-gdb/gdb/value.c:1347
        #2 0x555c497909cd in value_primitive_field(value*, long, int, type*) /home/simark/src/binutils-gdb/gdb/value.c:3126
        #3 0x555c478f2eaa in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:333
        #4 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #5 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #6 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #7 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #8 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #9 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #10 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #11 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #12 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #13 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048
        #14 0x555c49759b17 in common_val_print(value*, ui_file*, int, value_print_options const*, language_defn const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1151
        #15 0x555c478f2fcb in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:335
        #16 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #17 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #18 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #19 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #20 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #21 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048
        #22 0x555c49759b17 in common_val_print(value*, ui_file*, int, value_print_options const*, language_defn const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1151
        #23 0x555c478f2fcb in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:335
        #24 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #25 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #26 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #27 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048
        #28 0x555c49759b17 in common_val_print(value*, ui_file*, int, value_print_options const*, language_defn const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1151
        #29 0x555c4760f04c in c_value_print(value*, ui_file*, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:587
        #30 0x555c483ff954 in language_defn::value_print(value*, ui_file*, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:614
        #31 0x555c49759f61 in value_print(value*, ui_file*, value_print_options const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1189
        #32 0x555c48950f70 in print_formatted /home/simark/src/binutils-gdb/gdb/printcmd.c:337
        #33 0x555c48958eda in print_value(value*, value_print_options const&) /home/simark/src/binutils-gdb/gdb/printcmd.c:1258
        #34 0x555c48959891 in print_command_1 /home/simark/src/binutils-gdb/gdb/printcmd.c:1367
        #35 0x555c4895a3df in print_command /home/simark/src/binutils-gdb/gdb/printcmd.c:1458
        #36 0x555c4767f974 in do_simple_func /home/simark/src/binutils-gdb/gdb/cli/cli-decode.c:97
        #37 0x555c47692e25 in cmd_func(cmd_list_element*, char const*, int) /home/simark/src/binutils-gdb/gdb/cli/cli-decode.c:2475
        #38 0x555c4936107e in execute_command(char const*, int) /home/simark/src/binutils-gdb/gdb/top.c:670
        #39 0x555c485f1bff in catch_command_errors /home/simark/src/binutils-gdb/gdb/main.c:523
        #40 0x555c485f249c in execute_cmdargs /home/simark/src/binutils-gdb/gdb/main.c:618
        #41 0x555c485f6677 in captured_main_1 /home/simark/src/binutils-gdb/gdb/main.c:1317
        #42 0x555c485f6c83 in captured_main /home/simark/src/binutils-gdb/gdb/main.c:1338
        #43 0x555c485f6d65 in gdb_main(captured_main_args*) /home/simark/src/binutils-gdb/gdb/main.c:1363
        #44 0x555c46e41ba8 in main /home/simark/src/binutils-gdb/gdb/gdb.c:32
        #45 0x7f71198bcb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        #46 0x555c46e4197d in _start (/home/simark/build/binutils-gdb-one-target/gdb/gdb+0x77f197d)

    0x6020000c52af is located 1 bytes to the left of 8-byte region [0x6020000c52b0,0x6020000c52b8)
    allocated by thread T0 here:
        #0 0x7f711b2b7459 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
        #1 0x555c470acdc9 in xcalloc /home/simark/src/binutils-gdb/gdb/alloc.c:100
        #2 0x555c49b775cd in xzalloc(unsigned long) /home/simark/src/binutils-gdb/gdbsupport/common-utils.cc:29
        #3 0x555c4977bdeb in allocate_value_contents /home/simark/src/binutils-gdb/gdb/value.c:1029
        #4 0x555c4977be25 in allocate_value(type*) /home/simark/src/binutils-gdb/gdb/value.c:1040
        #5 0x555c4979030d in value_primitive_field(value*, long, int, type*) /home/simark/src/binutils-gdb/gdb/value.c:3092
        #6 0x555c478f6280 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:501
        #7 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #8 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #9 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #10 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #11 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #12 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #13 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #14 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #15 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048
        #16 0x555c49759b17 in common_val_print(value*, ui_file*, int, value_print_options const*, language_defn const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1151
        #17 0x555c478f2fcb in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:335
        #18 0x555c478f63b2 in cp_print_value /home/simark/src/binutils-gdb/gdb/cp-valprint.c:513
        #19 0x555c478f02ca in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:161
        #20 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #21 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #22 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #23 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048
        #24 0x555c49759b17 in common_val_print(value*, ui_file*, int, value_print_options const*, language_defn const*) /home/simark/src/binutils-gdb/gdb/valprint.c:1151
        #25 0x555c478f2fcb in cp_print_value_fields(value*, ui_file*, int, value_print_options const*, type**, int) /home/simark/src/binutils-gdb/gdb/cp-valprint.c:335
        #26 0x555c4760d45f in c_value_print_struct /home/simark/src/binutils-gdb/gdb/c-valprint.c:383
        #27 0x555c4760df4c in c_value_print_inner(value*, ui_file*, int, value_print_options const*) /home/simark/src/binutils-gdb/gdb/c-valprint.c:438
        #28 0x555c483ff9a7 in language_defn::value_print_inner(value*, ui_file*, int, value_print_options const*) const /home/simark/src/binutils-gdb/gdb/language.c:632
        #29 0x555c49758b68 in do_val_print /home/simark/src/binutils-gdb/gdb/valprint.c:1048

Since there are some binaries with this in the wild, I think it would be
useful for GDB to work around this.  I did the obvious simple thing, if
the DW_AT_data_member_location's value is -1, replace it with 0.  I
added a producer check to only apply this fixup for GCC 11.  The idea is
that if some other compiler ever uses a DW_AT_data_member_location value
of -1 by mistake, we don't know (before analyzing the bug at least) if
they did mean 0 or some other value.  So I wouldn't want to apply the
fixup in that case.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28063
Change-Id: Ieef3459b0b9bbce8bdad838ba83b4b64e7269d42
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