From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by sourceware.org (Postfix) with ESMTPS id C204A3858C39 for ; Sat, 21 Jan 2023 07:48:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org C204A3858C39 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.de Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 52A3433B13 for ; Sat, 21 Jan 2023 07:48:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1674287288; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Bza8dMa+HusPWlsESexr7QA5WgGsfpE2eGzEi+I0Wug=; b=IkCMYEaHG/XDl6vreBz1B+82e2Q/V9WYG3bslDnsbYwLv2F5qmpIhZFJZ9OcbcOCW7bAmB Jg/bWbeiyIxkYd9CzQUWGWT5JerIaWpasmsYRnVHZN17piyKFXq1+sBGOKIxrswo+HcfSG Vl9zvNOjVlzv4A+1vQoqgOj38BPQiiI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1674287288; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Bza8dMa+HusPWlsESexr7QA5WgGsfpE2eGzEi+I0Wug=; b=GMQYtUJro8EELUWjzh38MB22+n9XZlY2DvaulIC/qbZi6uqdf2x35ulaagxOw2SeoMjp1a mC1RokCIwYgrguBA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 329D4138FE for ; Sat, 21 Jan 2023 07:48:08 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id DnIbC7iYy2McNwAAMHmgww (envelope-from ) for ; Sat, 21 Jan 2023 07:48:08 +0000 From: Tom de Vries To: gdb-patches@sourceware.org Subject: [RFC] [gdb/tdep] Assume epilogue unwind info is valid unless gcc < 4.5.0 Date: Sat, 21 Jan 2023 08:48:07 +0100 Message-Id: <20230121074807.22032-1-tdevries@suse.de> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,KAM_NUMSUBJECT,KAM_SHORT,SPF_HELO_NONE,SPF_PASS,TXREP 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: The gcc 4.4.x (and earlier) compilers had the problem that the unwind info in the epilogue was inaccurate. In order to work around this in gdb, epilogue unwinders were added with a higher priority than the dwarf unwinders in the amd64 and i386 targets: - amd64_epilogue_frame_unwind, and - i386_epilogue_frame_unwind see: - submission emails: https://sourceware.org/pipermail/gdb-patches/2009-July/066779.html https://sourceware.org/pipermail/gdb-patches/2009-August/067684.html - gdb commits 872761f485e and 06da04c6105 Subsequently, the epilogue unwind info problem got fixed in gcc 4.5.0, see: - submission email https://gcc.gnu.org/pipermail/gcc-patches/2009-May/261377.html - gcc commit cd9c1ca866b - release notes gcc 4.5.0 ( https://gcc.gnu.org/gcc-4.5/changes.html ): GCC now generates unwind info also for epilogues. However, the epilogue unwinders prevented gdb from taking advantage of the fixed epilogue unwind info, so the scope of the epilogue unwinders was limited, bailing out for gcc >= 4.5.0, see: - submisssion email https://sourceware.org/pipermail/gdb-patches/2011-June/083429.html - gdb commit e0d00bc749e "Disable epilogue unwinders on recent GCCs" This scope limitation mechanism works well for gcc -g: the producer is available in the debug info, and we can determine whether we're dealing with reliable epilogue unwind info or not. For gcc -g0 though, epilogue unwind information is available in .eh_frame, but the producer is not availabe to determine whether that information is reliable or not, and consequently the info is ignored: - in the case of using gcc <= 4.4.x, that is the ok decision and we're working around the gcc problem, but - in the case of gcc >= 4.5.0, that means we fail to take advantage of fixed epilogue unwind info. Furthermore, let's review the history of what epilogue unwind information is trusted by gdb: - initial position: trust all information - after the epilogue unwinders were added: trust none - after the scope limitation: only trust gcc >= 4.5.0. So, while we started out with trusting info from all compilers, we end up trusting only gcc >= 4.5.0, which seems a bit of an overreach for a workaround for a problem in the gcc compiler. Fix these two issues by reversing the burden of proof: - currently we assume epilogue unwind info is invalid unless we can proof that gcc >= 4.5.0. - instead, assume epilogue unwind info is valid unless we can proof that gcc < 4.5.0. An added benefit of this is that it makes the amd64 and i386 targets more similar to other targets, which makes comparing behaviour easier. Note that some other targets also have an epilogue unwinder, but none of those have a higher priority than the dwarf unwinders. Tested on x86_64-linux with gcc 7.5.0, with target boards unix/-m64 and unix/-m32. PR tdep/30028 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30028 --- gdb/amd64-tdep.c | 5 ++++- gdb/dwarf2/read.c | 10 +++++++++- gdb/i386-tdep.c | 5 ++++- 3 files changed, 17 insertions(+), 3 deletions(-) diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c index 70d0d0f3318..c19220d006d 100644 --- a/gdb/amd64-tdep.c +++ b/gdb/amd64-tdep.c @@ -2906,7 +2906,10 @@ amd64_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc) struct compunit_symtab *cust; cust = find_pc_compunit_symtab (pc); - if (cust != NULL && cust->epilogue_unwind_valid ()) + if (/* In absence of producer information, optimistically assume that we're + not dealing with gcc < 4.5.0. */ + cust == NULL + || cust->epilogue_unwind_valid ()) return 0; if (target_read_memory (pc, &insn, 1)) diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index cd937f24ee7..40869f708e3 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -8484,7 +8484,15 @@ process_full_comp_unit (dwarf2_cu *cu, enum language pretend_language) if (cu->has_loclist && gcc_4_minor >= 5) cust->set_locations_valid (true); - if (gcc_4_minor >= 5) + if (cu->producer == nullptr) + /* In absence of producer information, optimistically assume that we're + not dealing with gcc < 4.5.0. */ + cust->set_epilogue_unwind_valid (true); + if (!producer_is_gcc (cu->producer, nullptr, nullptr)) + /* Not gcc. */ + cust->set_epilogue_unwind_valid (true); + else if (gcc_4_minor >= 5) + /* gcc >= 4.5.0. */ cust->set_epilogue_unwind_valid (true); cust->set_call_site_htab (cu->call_site_htab); diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c index 580664d2ce5..4eab2e6f7a3 100644 --- a/gdb/i386-tdep.c +++ b/gdb/i386-tdep.c @@ -2222,7 +2222,10 @@ i386_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc) struct compunit_symtab *cust; cust = find_pc_compunit_symtab (pc); - if (cust != NULL && cust->epilogue_unwind_valid ()) + if (/* In absence of producer information, optimistically assume that we're + not dealing with gcc < 4.5.0. */ + cust == NULL + || cust->epilogue_unwind_valid ()) return 0; if (target_read_memory (pc, &insn, 1)) base-commit: 76f8ef8d53792ef89aee7a51b94bc7d1cf324379 -- 2.35.3