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MID_RHS_MATCH_FROM(0.00)[]; PREVIOUSLY_DELIVERED(0.00)[gdb-patches@sourceware.org]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo, imap1.dmz-prg2.suse.org:rdns, sourceware.org:url, suse.de:dkim, suse.de:mid] X-Rspamd-Queue-Id: 320E85BD20 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 4/2/26 10:49 AM, 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 happens 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. > > 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: > - 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 > > 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 > --- > 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: 8ee110dee1942a20fd206c7107a027e9b04ba56e