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b=qO7M/7sw7gDdsTmAkgli+GHp2u326lbYBwSC1klT4P3CqOj8pVyeSg3kgW/cWML7QCaDaQ ndFhcgHDF4hYZRBw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id CFFA01340C; Tue, 29 Apr 2025 11:50:13 +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 kBoNMfW8EGjhSAAAD6G6ig (envelope-from ); Tue, 29 Apr 2025 11:50:13 +0000 Message-ID: <6195c78a-7810-4aba-bd5b-8110d556d72e@suse.de> Date: Tue, 29 Apr 2025 13:50:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] [gdb] Fix sig_write for null gdb_stderr To: Simon Marchi , gdb-patches@sourceware.org References: <20250425171845.9934-1-tdevries@suse.de> <20250425171845.9934-2-tdevries@suse.de> <4d29d800-175e-453f-9743-4413431d3c56@simark.ca> Content-Language: en-US From: Tom de Vries In-Reply-To: <4d29d800-175e-453f-9743-4413431d3c56@simark.ca> Content-Type: text/plain; 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DKIM_TRACE(0.00)[suse.de:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo, imap1.dmz-prg2.suse.org:rdns, suse.de:dkim, suse.de:mid] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action 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 4/28/25 17:17, Simon Marchi wrote: > On 4/25/25 1:18 PM, Tom de Vries wrote: >> When running test-case gdb.tui/tui-layout-asm.exp with target board >> dwarf5-fission-debug-types, the test-case fails and I get a core dump: >> ... >> # of unexpected core files 1 >> ... >> >> Looking at the backtrace of the core file, what seems to be happening is that: >> - gdbpy_flush attempts to flush gdb_stdout, which is nullptr >> - that causes a segfault >> - gdb intercepts this and starts to handle it using handle_fatal_signal >> - handle_fatal_signal calls sig_write, which attempts to write to gdb_stderr, >> which is nullptr, >> - that causes another segfault >> - gdb exits >> >> I managed to reproduce the problem by the following trigger patch in >> stdin_event_handler: >> ... >> - if (error) >> + if (1 || error) >> { >> current_ui = main_ui; >> ui->unregister_file_handler (); >> - if (main_ui == ui) >> + if (1 || main_ui == ui) >> { >> gdb_printf (gdb_stderr, _("error detected on stdin\n")); >> + gdb_stderr = nullptr; >> + gdb_stdout = nullptr; >> + gdb_stdlog = nullptr; >> quit_command ((char *) 0, 0); >> } >> ... >> which gives us: >> ... >> $ gdb >> (gdb) error detected on stdin >> Segmentation fault (core dumped) >> $ q >> ... >> >> Fix sig_write to handle the case that gdb_stderr == nullptr, such that we get >> instead: >> ... >> $ gdb >> (gdb) error detected on stdin >> >> Fatal signal: Segmentation fault >> ----- Backtrace ----- >> ... >> --------------------- >> A fatal error internal to GDB has been detected, further >> debugging is not possible. GDB will now terminate. >> >> This is a bug, please report it. For instructions, see: >> . >> >> Segmentation fault (core dumped) >> $ q >> ... >> >> Tested on x86_64-linux. >> --- >> gdb/bt-utils.c | 30 +++++++++++++++++++++--------- >> gdb/event-top.c | 13 +++++++++++-- >> 2 files changed, 32 insertions(+), 11 deletions(-) >> >> diff --git a/gdb/bt-utils.c b/gdb/bt-utils.c >> index 8e782450ae9..9e9f680f9ea 100644 >> --- a/gdb/bt-utils.c >> +++ b/gdb/bt-utils.c >> @@ -55,7 +55,10 @@ libbacktrace_error (void *data, const char *errmsg, int errnum) >> >> const auto sig_write = [] (const char *msg) -> void >> { >> - gdb_stderr->write_async_safe (msg, strlen (msg)); >> + if (gdb_stderr == nullptr || gdb_stderr->fd () == -1) >> + std::ignore = ::write (2, msg, strlen (msg)); > > TIL about std::ignore. > > Is it possible to factor out the lambdas: > > const auto sig_write = [] (const char *msg) -> void > { > if (gdb_stderr == nullptr || gdb_stderr->fd () == -1) > std::ignore = ::write (2, msg, strlen (msg)); > else > gdb_stderr->write_async_safe (msg, strlen (msg)); > }; > > to a function? At first glance they all seem to be the same. > I've done this in a v2 ( https://sourceware.org/pipermail/gdb-patches/2025-April/217564.html ) in a separate patch. Thanks, - Tom > Otherwise, LGTM. > > Approved-By: Simon Marchi > > Simon