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Sun, 12 Nov 2023 12:21:04 -0800 (PST) X-Google-Smtp-Source: AGHT+IEcCTwXZk5vZkyJkiwytC5P/ikusvQNFvH6CUlvTP409hI7DsyMY/ObaB85f0fB6bfUv/XcnMvfRUIHG1A+e50= X-Received: by 2002:a05:6871:2211:b0:1e9:ae68:fda1 with SMTP id sc17-20020a056871221100b001e9ae68fda1mr6521846oab.1.1699820463800; Sun, 12 Nov 2023 12:21:03 -0800 (PST) MIME-Version: 1.0 References: <20231028002008.1105723-1-amerey@redhat.com> <20231028002008.1105723-3-amerey@redhat.com> In-Reply-To: <20231028002008.1105723-3-amerey@redhat.com> From: Aaron Merey Date: Sun, 12 Nov 2023 15:20:52 -0500 Message-ID: Subject: Re: [PATCH 2/4 v2] gdb/progspace: Add reverse safe iterator and template for unwrapping iterator To: gdb-patches@sourceware.org Cc: aburgess@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-10.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,RCVD_IN_SORBS_WEB,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Ping Thanks, Aaron On Fri, Oct 27, 2023 at 8:20=E2=80=AFPM Aaron Merey wro= te: > > v1: https://sourceware.org/pipermail/gdb-patches/2023-June/199984.html > > v2 removes unwrapping_reverse_objfile_iterator and adds > basic_safe_reverse_range and basic_safe_reverse_iterator. > > Commit message: > > This patch changes progspace objfile_list insertion so that separate > debug objfiles are placed into the list after the parent objfile, > instead of before. Additionally qf_require_partial_symbols now returns > a safe_range. > > These changes are intended to prepare gdb for on-demand debuginfo > downloading and the downloading of .gdb_index sections. > > With on-demand downloading enabled, gdb might need to delete a > .gdb_index quick_symbol_functions from a parent objfile while looping > the objfile's list of quick_symbol_functions becasue the separate > debug objfile has just been downloaded. The use of a safe_range > prevents this removal from causing iterator invalidation. > > gdb might also download a debuginfo file during symtab expansion. > In this case an objfile will be added to the current progspace's > objfiles_list during iteration over the list (for example, in > iterate_over_symtabs). We want these loops to also iterate over > newly downloaded objfiles. So objfiles need to be inserted into > objfiles_list after their parent since it is during the search of > the parent objfile for some symbol or filename that the separate > debug objfile might be downloaded. > > To facilitate the safe deletion of objfiles, this patch also adds > basic_safe_reverse_range and basic_safe_reverse_iterator. This allows > objfiles to be removed from the objfiles_list in a loop without iterator > invalidation. > > If a forward safe iterator were to be used, the deletion of an > objfile could invalidate the safe iterator's reference to the next > objfile in the objfiles_list. This can happen when the deletion > of an objfile causes the deletion of a separate debug objfile that > happens to the be next element in the objfiles_list. > > The standard reverse iterator is not suitable for safe objfile deletion. > In order to safely delete the first objfile in the objfiles_list, the > standard reverse iterator's underlying begin iterator would have to be > decremented, resulting in undefined behavior. > > A small change was also made to a testcase in py-objfile.exp to > account for the new placement of separate debug objfiles in > objfiles_list. > --- > gdb/jit.c | 7 +- > gdb/objfiles.c | 8 +- > gdb/objfiles.h | 8 +- > gdb/progspace.c | 19 ++++- > gdb/progspace.h | 31 ++++--- > gdb/testsuite/gdb.python/py-objfile.exp | 2 +- > gdbsupport/safe-iterator.h | 106 ++++++++++++++++++++++++ > 7 files changed, 154 insertions(+), 27 deletions(-) > > diff --git a/gdb/jit.c b/gdb/jit.c > index 9e8325ab803..a39fdc5a96d 100644 > --- a/gdb/jit.c > +++ b/gdb/jit.c > @@ -1240,11 +1240,10 @@ jit_breakpoint_re_set (void) > static void > jit_inferior_exit_hook (struct inferior *inf) > { > - for (objfile *objf : current_program_space->objfiles_safe ()) > + current_program_space->unlink_objfiles_if ([&] (const objfile *objf) > { > - if (objf->jited_data !=3D nullptr && objf->jited_data->addr !=3D 0= ) > - objf->unlink (); > - } > + return (objf->jited_data !=3D nullptr) && (objf->jited_data->addr = !=3D 0); > + }); > } > > void > diff --git a/gdb/objfiles.c b/gdb/objfiles.c > index 8f085b1bb7c..9822c179962 100644 > --- a/gdb/objfiles.c > +++ b/gdb/objfiles.c > @@ -793,14 +793,12 @@ have_full_symbols (void) > void > objfile_purge_solibs (void) > { > - for (objfile *objf : current_program_space->objfiles_safe ()) > + current_program_space->unlink_objfiles_if ([&] (const objfile *objf) > { > /* We assume that the solib package has been purged already, or wi= ll > be soon. */ > - > - if (!(objf->flags & OBJF_USERLOADED) && (objf->flags & OBJF_SHARED= )) > - objf->unlink (); > - } > + return !(objf->flags & OBJF_USERLOADED) && (objf->flags & OBJF_SHA= RED); > + }); > } > > > diff --git a/gdb/objfiles.h b/gdb/objfiles.h > index 4b8aa9bfcec..c20b63ceadf 100644 > --- a/gdb/objfiles.h > +++ b/gdb/objfiles.h > @@ -698,13 +698,17 @@ struct objfile > > private: > > + using qf_list =3D std::forward_list; > + using qf_range =3D iterator_range; > + using qf_safe_range =3D basic_safe_range; > + > /* Ensure that partial symbols have been read and return the "quick" (= aka > partial) symbol functions for this symbol reader. */ > - const std::forward_list & > + qf_safe_range > qf_require_partial_symbols () > { > this->require_partial_symbols (true); > - return qf; > + return qf_safe_range (qf_range (qf.begin (), qf.end ())); > } > > public: > diff --git a/gdb/progspace.c b/gdb/progspace.c > index 839707e9d71..c0fca1dace7 100644 > --- a/gdb/progspace.c > +++ b/gdb/progspace.c > @@ -143,19 +143,19 @@ program_space::free_all_objfiles () > > void > program_space::add_objfile (std::unique_ptr &&objfile, > - struct objfile *before) > + struct objfile *after) > { > - if (before =3D=3D nullptr) > + if (after =3D=3D nullptr) > objfiles_list.push_back (std::move (objfile)); > else > { > auto iter =3D std::find_if (objfiles_list.begin (), objfiles_list.= end (), > [=3D] (const std::unique_ptr<::objfile> &= objf) > { > - return objf.get () =3D=3D before; > + return objf.get () =3D=3D after; > }); > gdb_assert (iter !=3D objfiles_list.end ()); > - objfiles_list.insert (iter, std::move (objfile)); > + objfiles_list.insert (++iter, std::move (objfile)); > } > } > > @@ -184,6 +184,17 @@ program_space::remove_objfile (struct objfile *objfi= le) > > /* See progspace.h. */ > > +void > +program_space::unlink_objfiles_if > + (gdb::function_view predicate) > +{ > + for (auto &it : objfiles_safe ()) > + if (predicate (it.get ())) > + it->unlink (); > +} > + > +/* See progspace.h. */ > + > struct objfile * > program_space::objfile_for_address (CORE_ADDR address) > { > diff --git a/gdb/progspace.h b/gdb/progspace.h > index a22e427400e..17bb1710ccf 100644 > --- a/gdb/progspace.h > +++ b/gdb/progspace.h > @@ -214,28 +214,32 @@ struct program_space > unwrapping_objfile_iterator (objfiles_list.end ())); > } > > - using objfiles_safe_range =3D basic_safe_range; > + using objfiles_safe_range =3D iterator_range; > + using objfiles_safe_reverse_range > + =3D basic_safe_reverse_range; > > /* An iterable object that can be used to iterate over all objfiles. > The basic use is in a foreach, like: > > for (objfile *objf : pspace->objfiles_safe ()) { ... } > > - This variant uses a basic_safe_iterator so that objfiles can be > - deleted during iteration. */ > - objfiles_safe_range objfiles_safe () > + This variant uses a basic_safe_reverse_iterator so that objfiles > + can be deleted during iteration. > + > + The use of a reverse iterator helps ensure that separate debug > + objfiles are deleted before their parent objfile. This prevents > + iterator invalidation due to the deletion of a parent objfile. */ > + objfiles_safe_reverse_range objfiles_safe () > { > - return objfiles_safe_range > - (objfiles_range > - (unwrapping_objfile_iterator (objfiles_list.begin ()), > - unwrapping_objfile_iterator (objfiles_list.end ()))); > + return objfiles_safe_reverse_range > + (objfiles_safe_range (objfiles_list.begin (), objfiles_list.end ()= )); > } > > - /* Add OBJFILE to the list of objfiles, putting it just before > - BEFORE. If BEFORE is nullptr, it will go at the end of the > + /* Add OBJFILE to the list of objfiles, putting it just after > + AFTER. If AFTER is nullptr, it will go at the end of the > list. */ > void add_objfile (std::unique_ptr &&objfile, > - struct objfile *before); > + struct objfile *after); > > /* Remove OBJFILE from the list of objfiles. */ > void remove_objfile (struct objfile *objfile); > @@ -250,6 +254,11 @@ struct program_space > /* Free all the objfiles associated with this program space. */ > void free_all_objfiles (); > > + /* Unlink all objfiles associated with this program space for which > + PREDICATE evaluates to true. */ > + void unlink_objfiles_if > + (gdb::function_view predicate); > + > /* Return the objfile containing ADDRESS, or nullptr if the address > is outside all objfiles in this progspace. */ > struct objfile *objfile_for_address (CORE_ADDR address); > diff --git a/gdb/testsuite/gdb.python/py-objfile.exp b/gdb/testsuite/gdb.= python/py-objfile.exp > index 61b9942de79..0bf49976b73 100644 > --- a/gdb/testsuite/gdb.python/py-objfile.exp > +++ b/gdb/testsuite/gdb.python/py-objfile.exp > @@ -135,7 +135,7 @@ gdb_test "p main" "=3D {} $hex
" \ > gdb_py_test_silent_cmd "python objfile.add_separate_debug_file(\"${binfi= le}\")" \ > "Add separate debug file file" 1 > > -gdb_py_test_silent_cmd "python sep_objfile =3D gdb.objfiles()\[0\]" \ > +gdb_py_test_silent_cmd "python sep_objfile =3D gdb.objfiles()\[1\]" \ > "Get separate debug info objfile" 1 > > gdb_test "python print (sep_objfile.owner.filename)" "${testfile}2" \ > diff --git a/gdbsupport/safe-iterator.h b/gdbsupport/safe-iterator.h > index ccd772ca2a5..9f57c1543cf 100644 > --- a/gdbsupport/safe-iterator.h > +++ b/gdbsupport/safe-iterator.h > @@ -136,4 +136,110 @@ class basic_safe_range > Range m_range; > }; > > +/* A reverse basic_safe_iterator. See basic_safe_iterator for intended = use. */ > + > +template > +class basic_safe_reverse_iterator > +{ > +public: > + typedef basic_safe_reverse_iterator self_type; > + typedef typename Iterator::value_type value_type; > + typedef typename Iterator::reference reference; > + typedef typename Iterator::pointer pointer; > + typedef typename Iterator::iterator_category iterator_category; > + typedef typename Iterator::difference_type difference_type; > + > + /* Construct the iterator using ARG, and construct the end iterator > + using ARG2. */ > + template > + explicit basic_safe_reverse_iterator (Arg &&arg, Arg &&arg2) > + : m_begin (std::forward (arg)), > + m_end (std::forward (arg2)), > + m_it (m_end), > + m_next (m_end) > + { > + /* M_IT and M_NEXT are initialized as one-past-end. Set M_IT to poi= nt > + to the last element and set M_NEXT to point to the second last el= ement, > + if such elements exist. */ > + if (m_it !=3D m_begin) > + { > + --m_it; > + > + if (m_it !=3D m_begin) > + { > + --m_next; > + --m_next; > + } > + } > + } > + > + typename gdb::invoke_result:= :type > + operator* () const > + { return *m_it; } > + > + self_type &operator++ () > + { > + m_it =3D m_next; > + > + if (m_it !=3D m_end) > + { > + /* Use M_BEGIN only if we sure that it is valid. */ > + if (m_it =3D=3D m_begin) > + m_next =3D m_end; > + else > + --m_next; > + } > + > + return *this; > + } > + > + bool operator=3D=3D (const self_type &other) const > + { return m_it =3D=3D other.m_it; } > + > + bool operator!=3D (const self_type &other) const > + { return m_it !=3D other.m_it; } > + > +private: > + /* The first element. */ > + Iterator m_begin {}; > + > + /* A one-past-end iterator. */ > + Iterator m_end {}; > + > + /* The current element. */ > + Iterator m_it {}; > + > + /* The next element. Always one element ahead of M_IT. */ > + Iterator m_next {}; > +}; > + > +/* A range adapter that wraps a forward range, and then returns > + safe reverse iterators wrapping the original range's iterators. */ > + > +template > +class basic_safe_reverse_range > +{ > +public: > + > + typedef basic_safe_reverse_iterator iterator= ; > + > + explicit basic_safe_reverse_range (Range range) > + : m_range (range) > + { > + } > + > + iterator begin () > + { > + return iterator (m_range.begin (), m_range.end ()); > + } > + > + iterator end () > + { > + return iterator (m_range.end (), m_range.end ()); > + } > + > +private: > + > + Range m_range; > +}; > #endif /* COMMON_SAFE_ITERATOR_H */ > -- > 2.41.0 >