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Thu, 30 Jul 2026 08:17:14 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id SWvTK4oIa2ryLQAAD6G6ig (envelope-from ) for ; Thu, 30 Jul 2026 08:17:14 +0000 Message-ID: <16b9b910-4c6a-4827-8f90-b60f2c563a52@suse.de> Date: Thu, 30 Jul 2026 10:17:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PING][PATCH v3] [gdb] Fix segfault in sig_write From: Tom de Vries To: gdb-patches@sourceware.org References: <20260423144340.3193734-1-tdevries@suse.de> Content-Language: en-US In-Reply-To: <20260423144340.3193734-1-tdevries@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: C73253EE7 X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_TLS_ALL(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_ONE(0.00)[1]; ARC_NA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[sourceware.org:url,suse.de:mid,suse.de:dkim,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received,2a07:de40:b281:104:10:150:64:97:from]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; TO_DN_NONE(0.00)[]; PREVIOUSLY_DELIVERED(0.00)[gdb-patches@sourceware.org]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 4/23/26 4:43 PM, Tom de Vries wrote: > I ran into a segfault in sig_write: > ... > if (gdb_stderr == nullptr || gdb_stderr->fd () == -1) > ... > > [ A regression since commit 817003ed469 ("Rewrite output redirection and > logging"). ] > > This happened as follows. > > First, we get gdb_stderr by calling current_gdb_stderr, which returns > current_ui.current_interpreter.m_stderr.get (), which is not nullptr. > > Then we do "gdb_stderr->fd ()", which gets us to > wrapped_file >::fd: > ... > int fd () const override > { return m_stream->fd (); } > ... > > The "m_stream->" part brings us to: > ... > /* A "smart pointer" that references a particular member of the > current UI. */ > template > struct ui_file_ptr > { > ui_file *operator-> () const > { > return current_ui->*F; > } > }; > ... > which does "current_ui.m_ui_stderr" which indeed is nullptr. > > So why was current_ui.m_ui_stderr nullptr? This was due a problem fixed by > commit b171f68e945 ("[gdb/tui] Make tui_setup_io more robust"). > > So, atm as far as we know current_ui.m_ui_stderr is never nullptr. > > However, sig_write has special requirements because it's called when > "things go wrong", so we want it to work reliably in case things going wrong > means that again current_ui.m_ui_stderr is nullptr. > > Fix this in wrapped_file::fd by checking for a nullptr m_stream. > Ping. Thanks, - Tom > A v1 was submitted here [1]. > > Changes in v2 [2]: > - changed approach of fixing this: rather than trying to fix this in sig_write > by avoiding the use of gdb_stderr, fix this in wrapped_file::fd. > - added unit test > > Changes in v3: > - extended commit message to be more clear about how current_ui.m_ui_stderr > got to be a nullptr > > Tested on x86_64-linux. > > Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33918 > > [1] v1 https://sourceware.org/pipermail/gdb-patches/2026-February/225155.html > [2] v2 https://sourceware.org/pipermail/gdb-patches/2026-April/226295.html > --- > gdb/ui-file.h | 2 +- > gdb/ui.h | 4 ++++ > gdb/unittests/ui-file-selftests.c | 14 ++++++++++++++ > 3 files changed, 19 insertions(+), 1 deletion(-) > > diff --git a/gdb/ui-file.h b/gdb/ui-file.h > index 6a1d3964335..b7d3aebda9a 100644 > --- a/gdb/ui-file.h > +++ b/gdb/ui-file.h > @@ -420,7 +420,7 @@ class wrapped_file : public ui_file > { m_stream->emit_style_escape (style); } > > int fd () const override > - { return m_stream->fd (); } > + { return m_stream == nullptr ? -1 : m_stream->fd (); } > > void puts_unfiltered (const char *str) override > { m_stream->puts_unfiltered (str); } > diff --git a/gdb/ui.h b/gdb/ui.h > index 891660896ef..ef977470302 100644 > --- a/gdb/ui.h > +++ b/gdb/ui.h > @@ -163,6 +163,10 @@ struct ui > { > return current_ui->*F; > } > + bool operator== (nullptr_t p) const > + { > + return current_ui->*F == nullptr; > + } > }; > > /* A ui_file that simply forwards. */ > diff --git a/gdb/unittests/ui-file-selftests.c b/gdb/unittests/ui-file-selftests.c > index 69e48735001..b9c1aca3774 100644 > --- a/gdb/unittests/ui-file-selftests.c > +++ b/gdb/unittests/ui-file-selftests.c > @@ -48,6 +48,20 @@ run_tests () > scoped_restore save_7 = make_scoped_restore (&sevenbit_strings, true); > check_one ("more weird stuff: \xa5", '\\', > "more weird stuff: \\245"); > + > + { > + /* There's a bug that has the effect "*redirectable_stderr () == nullptr". > + In that case, gdb_stderr is not nullptr, but the underlying pointer is > + a nullptr. Check that "gdb_stderr->fd ()" doesn't dereference the > + underlying nullptr. > + This allows us to check for a usable gdb_stderr using > + "gdb_stderr != nullptr && gdb_stderr->fd () == -1", as we do in > + sig_write. */ > + scoped_restore restore_stderr > + = make_scoped_restore (redirectable_stderr (), nullptr); > + SELF_CHECK (gdb_stderr != nullptr); > + SELF_CHECK (gdb_stderr->fd () == -1); > + } > } > > } /* namespace file*/ > > base-commit: 8dc535c59fdbcf99e28703425e5c1c711e63a1f1