[PING][PATCH 1/3 v3] gdb/progspace: Add reverse safe iterator
Aaron Merey
amerey@redhat.com
Fri May 17 14:09:12 GMT 2024
Ping
Thanks,
Aaron
On Fri, May 3, 2024 at 6:59 PM Aaron Merey <amerey@redhat.com> wrote:
>
> This is a reposting of v3 from
> https://sourceware.org/pipermail/gdb-patches/2024-January/205955.html
>
> 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 because 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 | 14 +--
> gdb/objfiles.h | 17 +++-
> gdb/progspace.c | 19 +++-
> gdb/progspace.h | 31 ++++---
> gdb/symfile-debug.c | 34 +++----
> gdb/testsuite/gdb.python/py-objfile.exp | 2 +-
> gdbsupport/safe-iterator.h | 115 ++++++++++++++++++++++++
> 8 files changed, 195 insertions(+), 44 deletions(-)
>
> diff --git a/gdb/jit.c b/gdb/jit.c
> index 797be95a8da..90f9159fa9d 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 != nullptr && objf->jited_data->addr != 0)
> - objf->unlink ();
> - }
> + return (objf->jited_data != nullptr) && (objf->jited_data->addr != 0);
> + });
> }
>
> void
> diff --git a/gdb/objfiles.c b/gdb/objfiles.c
> index ba88ed1bc41..70017c7fb32 100644
> --- a/gdb/objfiles.c
> +++ b/gdb/objfiles.c
> @@ -469,6 +469,12 @@ objfile::unlink ()
> current_program_space->remove_objfile (this);
> }
>
> +qf_safe_range
> +objfile::qf_safe ()
> +{
> + return qf_safe_range (qf_range (qf.begin (), qf.end ()));
> +}
> +
> /* Free all separate debug objfile of OBJFILE, but don't free OBJFILE
> itself. */
>
> @@ -792,14 +798,12 @@ 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 will
> be soon. */
> -
> - if (!(objf->flags & OBJF_USERLOADED) && (objf->flags & OBJF_SHARED))
> - objf->unlink ();
> - }
> + return !(objf->flags & OBJF_USERLOADED) && (objf->flags & OBJF_SHARED);
> + });
> }
>
>
> diff --git a/gdb/objfiles.h b/gdb/objfiles.h
> index 8b8b7182e87..1c8f79a2826 100644
> --- a/gdb/objfiles.h
> +++ b/gdb/objfiles.h
> @@ -370,6 +370,12 @@ class separate_debug_iterator
>
> typedef iterator_range<separate_debug_iterator> separate_debug_range;
>
> +/* See objfile::qf_safe. */
> +
> +using qf_list = std::forward_list<quick_symbol_functions_up>;
> +using qf_range = iterator_range<qf_list::iterator>;
> +using qf_safe_range = basic_safe_range<qf_range>;
> +
> /* Sections in an objfile. The section offsets are stored in the
> OBJFILE. */
>
> @@ -767,8 +773,15 @@ struct objfile
> const struct sym_fns *sf = nullptr;
>
> /* The "quick" (aka partial) symbol functions for this symbol
> - reader. */
> - std::forward_list<quick_symbol_functions_up> qf;
> + reader. Many quick_symbol_functions methods may result
> + in the deletion of a quick_symbol_functions from this
> + qf_list. It is recommended that qf_safe be used to iterate
> + over the qf_list. */
> + qf_list qf;
> +
> + /* Returns an iterable object that allows for safe deletion during
> + iteration. See gdbsupport/safe-iterator.h. */
> + qf_safe_range qf_safe ();
>
> /* Per objfile data-pointers required by other GDB modules. */
>
> diff --git a/gdb/progspace.c b/gdb/progspace.c
> index 0deca3f2376..b1b2dfb30c8 100644
> --- a/gdb/progspace.c
> +++ b/gdb/progspace.c
> @@ -140,19 +140,19 @@ program_space::free_all_objfiles ()
>
> void
> program_space::add_objfile (std::unique_ptr<objfile> &&objfile,
> - struct objfile *before)
> + struct objfile *after)
> {
> - if (before == nullptr)
> + if (after == nullptr)
> objfiles_list.push_back (std::move (objfile));
> else
> {
> auto iter = std::find_if (objfiles_list.begin (), objfiles_list.end (),
> [=] (const std::unique_ptr<::objfile> &objf)
> {
> - return objf.get () == before;
> + return objf.get () == after;
> });
> gdb_assert (iter != objfiles_list.end ());
> - objfiles_list.insert (iter, std::move (objfile));
> + objfiles_list.insert (++iter, std::move (objfile));
> }
> }
>
> @@ -181,6 +181,17 @@ program_space::remove_objfile (struct objfile *objfile)
>
> /* See progspace.h. */
>
> +void
> +program_space::unlink_objfiles_if
> + (gdb::function_view<bool (const objfile *objfile)> 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 bbf54efa07a..4d5ac991849 100644
> --- a/gdb/progspace.h
> +++ b/gdb/progspace.h
> @@ -250,28 +250,32 @@ struct program_space
> unwrapping_objfile_iterator (objfiles_list.end ()));
> }
>
> - using objfiles_safe_range = basic_safe_range<objfiles_range>;
> + using objfiles_it_range = iterator_range<objfile_list::iterator>;
> + using objfiles_safe_reverse_range
> + = basic_safe_reverse_range<objfiles_it_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_it_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> &&objfile,
> - struct objfile *before);
> + struct objfile *after);
>
> /* Remove OBJFILE from the list of objfiles. */
> void remove_objfile (struct objfile *objfile);
> @@ -286,6 +290,11 @@ 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<bool (const objfile *objfile)> 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/symfile-debug.c b/gdb/symfile-debug.c
> index 86c7010b2d2..330a520dca6 100644
> --- a/gdb/symfile-debug.c
> +++ b/gdb/symfile-debug.c
> @@ -84,7 +84,7 @@ objfile::has_partial_symbols ()
> them, then that is an indication that they are in fact available. Without
> this function the symbols may have been already read in but they also may
> not be present in this objfile. */
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> retval = iter->has_symbols (this);
> if (retval)
> @@ -107,7 +107,7 @@ objfile::has_unexpanded_symtabs ()
> objfile_debug_name (this));
>
> bool result = false;
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> if (iter->has_unexpanded_symtabs (this))
> {
> @@ -132,7 +132,7 @@ objfile::find_last_source_symtab ()
> gdb_printf (gdb_stdlog, "qf->find_last_source_symtab (%s)\n",
> objfile_debug_name (this));
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> retval = iter->find_last_source_symtab (this);
> if (retval != nullptr)
> @@ -165,7 +165,7 @@ objfile::forget_cached_source_info ()
> }
> }
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->forget_cached_source_info (this);
> }
>
> @@ -212,7 +212,7 @@ objfile::map_symtabs_matching_filename
> return result;
> };
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> if (!iter->expand_symtabs_matching (this,
> match_one_filename,
> @@ -275,7 +275,7 @@ objfile::lookup_symbol (block_enum kind, const lookup_name_info &name,
> return true;
> };
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> if (!iter->expand_symtabs_matching (this,
> nullptr,
> @@ -305,7 +305,7 @@ objfile::print_stats (bool print_bcache)
> gdb_printf (gdb_stdlog, "qf->print_stats (%s, %d)\n",
> objfile_debug_name (this), print_bcache);
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->print_stats (this, print_bcache);
> }
>
> @@ -316,7 +316,7 @@ objfile::dump ()
> gdb_printf (gdb_stdlog, "qf->dump (%s)\n",
> objfile_debug_name (this));
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->dump (this);
> }
>
> @@ -331,7 +331,7 @@ objfile::expand_symtabs_for_function (const char *func_name)
> lookup_name_info base_lookup (func_name, symbol_name_match_type::FULL);
> lookup_name_info lookup_name = base_lookup.make_ignore_params ();
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->expand_symtabs_matching (this,
> nullptr,
> &lookup_name,
> @@ -349,7 +349,7 @@ objfile::expand_all_symtabs ()
> gdb_printf (gdb_stdlog, "qf->expand_all_symtabs (%s)\n",
> objfile_debug_name (this));
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->expand_all_symtabs (this);
> }
>
> @@ -367,7 +367,7 @@ objfile::expand_symtabs_with_fullname (const char *fullname)
> return filename_cmp (basenames ? basename : fullname, filename) == 0;
> };
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->expand_symtabs_matching (this,
> file_matcher,
> nullptr,
> @@ -399,7 +399,7 @@ objfile::expand_symtabs_matching
> host_address_to_string (&expansion_notify),
> domain_name (domain).c_str ());
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> if (!iter->expand_symtabs_matching (this, file_matcher, lookup_name,
> symbol_matcher, expansion_notify,
> search_flags, domain))
> @@ -424,7 +424,7 @@ objfile::find_pc_sect_compunit_symtab (struct bound_minimal_symbol msymbol,
> host_address_to_string (section),
> warn_if_readin);
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> retval = iter->find_pc_sect_compunit_symtab (this, msymbol, pc, section,
> warn_if_readin);
> @@ -452,7 +452,7 @@ objfile::map_symbol_filenames (gdb::function_view<symbol_filename_ftype> fun,
> objfile_debug_name (this),
> need_fullname);
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->map_symbol_filenames (this, fun, need_fullname);
> }
>
> @@ -464,7 +464,7 @@ objfile::compute_main_name ()
> "qf->compute_main_name (%s)\n",
> objfile_debug_name (this));
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> iter->compute_main_name (this);
> }
>
> @@ -478,7 +478,7 @@ objfile::find_compunit_symtab_by_address (CORE_ADDR address)
> hex_string (address));
>
> struct compunit_symtab *result = NULL;
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> result = iter->find_compunit_symtab_by_address (this, address);
> if (result != nullptr)
> @@ -503,7 +503,7 @@ objfile::lookup_global_symbol_language (const char *name,
> enum language result = language_unknown;
> *symbol_found_p = false;
>
> - for (const auto &iter : qf)
> + for (const auto &iter : qf_safe ())
> {
> result = iter->lookup_global_symbol_language (this, name, domain,
> symbol_found_p);
> diff --git a/gdb/testsuite/gdb.python/py-objfile.exp b/gdb/testsuite/gdb.python/py-objfile.exp
> index 2f5b7752b43..8460c300de0 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" "= {<text variable, no debug info>} $hex <main>" \
> gdb_py_test_silent_cmd "python objfile.add_separate_debug_file(\"${binfile}\")" \
> "Add separate debug file file" 1
>
> -gdb_py_test_silent_cmd "python sep_objfile = gdb.objfiles()\[0\]" \
> +gdb_py_test_silent_cmd "python sep_objfile = 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 f69f3896758..be23cf7920a 100644
> --- a/gdbsupport/safe-iterator.h
> +++ b/gdbsupport/safe-iterator.h
> @@ -136,4 +136,119 @@ class basic_safe_range
> Range m_range;
> };
>
> +/* A reverse basic_safe_iterator. See basic_safe_iterator for intended use. */
> +
> +template<typename Iterator>
> +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. ARG and ARG2 should be forward iterators, typically
> + from begin and end methods, respectively.
> +
> + For example if ARG1 is created with container.begin and ARG2 is
> + is created with container.end, then the basic_safe_reverse_iterator
> + will traverse from the last element in the container to the first
> + element in the container. */
> + template<typename Arg>
> + explicit basic_safe_reverse_iterator (Arg &&arg, Arg &&arg2)
> + : m_begin (std::forward<Arg> (arg)),
> + m_end (std::forward<Arg> (arg2)),
> + m_it (m_end),
> + m_next (m_end)
> + {
> + /* M_IT and M_NEXT are initialized as one-past-end. Set M_IT to point
> + to the last element and set M_NEXT to point to the second last element,
> + if such elements exist. */
> + if (m_it != m_begin)
> + {
> + --m_it;
> +
> + if (m_it != m_begin)
> + {
> + --m_next;
> + --m_next;
> + }
> + }
> + }
> +
> + typename std::invoke_result<decltype(&Iterator::operator*), Iterator>::type
> + operator* () const
> + { return *m_it; }
> +
> + self_type &operator++ ()
> + {
> + m_it = m_next;
> +
> + if (m_it != m_end)
> + {
> + /* Use M_BEGIN only if we sure that it is valid. */
> + if (m_it == m_begin)
> + m_next = m_end;
> + else
> + --m_next;
> + }
> +
> + return *this;
> + }
> +
> + bool operator== (const self_type &other) const
> + { return m_it == other.m_it; }
> +
> + bool operator!= (const self_type &other) const
> + { return m_it != 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<typename Range>
> +class basic_safe_reverse_range
> +{
> +public:
> +
> + typedef basic_safe_reverse_iterator<typename Range::iterator> iterator;
> +
> + /* RANGE must be a forward range. basic_safe_reverse_iterators
> + will be used to traverse the forward range from the last element
> + to the first. */
> + 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 */
> --
> 2.43.0
>
More information about the Gdb-patches
mailing list