From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from rock.gnat.com (rock.gnat.com [IPv6:2620:20:4000:0:a9e:1ff:fe9b:1d1]) by sourceware.org (Postfix) with ESMTPS id 505AC3857BA8 for ; Wed, 27 Jul 2022 05:14:10 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 505AC3857BA8 Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id 1C7F311677B; Wed, 27 Jul 2022 01:14:10 -0400 (EDT) X-Virus-Scanned: Debian amavisd-new at gnat.com Received: from rock.gnat.com ([127.0.0.1]) by localhost (rock.gnat.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id j6CBZZiuQFUQ; Wed, 27 Jul 2022 01:14:10 -0400 (EDT) Received: from free.home (tron.gnat.com [IPv6:2620:20:4000:0:46a8:42ff:fe0e:e294]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by rock.gnat.com (Postfix) with ESMTPS id 7EAF2116771; Wed, 27 Jul 2022 01:14:03 -0400 (EDT) Received: from livre (livre.home [172.31.160.2]) by free.home (8.15.2/8.15.2) with ESMTPS id 26R5DqFm1760064 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 27 Jul 2022 02:13:53 -0300 From: Alexandre Oliva To: gcc-patches@gcc.gnu.org Cc: hubicka@ucw.cz, ubizjak@gmail.com, hjl.tools@gmail.com Subject: [PATCH] [PR83782] i386 PIE: avoid @GOTOFF for ifuncs and their aliases Organization: Free thinker, does not speak for AdaCore Errors-To: aoliva@lxoliva.fsfla.org Date: Wed, 27 Jul 2022 02:13:52 -0300 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 X-Spam-Status: No, score=-11.5 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, KAM_SHORT, KAM_STOCKGEN, 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 X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Jul 2022 05:14:12 -0000 g++.dg/ext/attr-ifunc-3.C and gcc.target/i386/mvc10.c, not changed, have made it clear that there were problems in the optimizations to use @GOTOFF to refer to locally-bound ifuncs. GNU ld as recently as May 2018 would reject such constructs, whereas later versions will silently accept but generate incorrect PIE with them (attr-ifunc-3.C) or still reject them if referenced through aliases (mvc10.c). The use of @GOTOFF for locally-bound but externally-visible symbols (e.g. protected visibility) also breaks pointer identity if the canonical address ends up preempted by a PLT entry. This patch modifies the local_symbolic_operand predicate to disable @GOTOFF for locally-bound symbols that would require @PLT for calls, restoring earlier behavior and disabling the optimization that has proven problematic even on amd64. Eventually we may reintroduce the optimization, when the linker is fixed and we test for the fix before enabling it, and we exclude symbols whose canonical addresses may be preempted even when the symbol definition can't. pr83782 tests have been adjusted to expect @GOT instead of @GOTOFF. Regstrapped on x86_64-linux-gnu; also tested, along with other patches I'm posting today with "i386 PIE" in the subject, and compared default-PIE and default-nonPIE results on it, and on i686-linux-gnu. Ok to install? for gcc/ChangeLog PR target/83782 * config/i386/predicates.md (local_symbolic_operand): Disable GOTOFF even for locally-bound ifuncs. * config/i386/i386.cc (ix86_call_use_plt_p): Follow the alias chain looking for an ifunc, as in gcc.target/i386/mvc10.c. for gcc/testsuite/ChangeLog PR target/83782 * gcc.target/i386/pr83782-1.c: Adjust to require GOT rather than GOTOFF on ia32. * gcc.target/i386/pr83782-2.c: Likewise. --- gcc/config/i386/i386.cc | 16 ++++++++++------ gcc/config/i386/predicates.md | 4 +++- gcc/testsuite/gcc.target/i386/pr83782-1.c | 4 ++-- gcc/testsuite/gcc.target/i386/pr83782-2.c | 4 ++-- 4 files changed, 17 insertions(+), 11 deletions(-) diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index aab28da4b5d4b..5c5dc8d2373ff 100644 --- a/gcc/config/i386/i386.cc +++ b/gcc/config/i386/i386.cc @@ -16058,13 +16058,17 @@ ix86_call_use_plt_p (rtx call_op) { if (SYMBOL_REF_DECL (call_op) && TREE_CODE (SYMBOL_REF_DECL (call_op)) == FUNCTION_DECL) - { - /* NB: All ifunc functions must be called via PLT. */ - cgraph_node *node - = cgraph_node::get (SYMBOL_REF_DECL (call_op)); - if (node && node->ifunc_resolver) + /* NB: All ifunc functions must be called via PLT, and we have + to explicitly iterate over an alias chain looking for a + node marked as an ifunc(_resolver) to tell. That node is + itself aliased to the actual resolver function, so + ultimate_alias_target would skip the marker, and the call + may be to another declaration aliased to the ifunc. */ + for (cgraph_node *node + = cgraph_node::get (SYMBOL_REF_DECL (call_op)); + node && node->alias; node = node->get_alias_target ()) + if (node->ifunc_resolver) return true; - } return false; } return true; diff --git a/gcc/config/i386/predicates.md b/gcc/config/i386/predicates.md index 42053ea7209f6..411c06e22e600 100644 --- a/gcc/config/i386/predicates.md +++ b/gcc/config/i386/predicates.md @@ -596,7 +596,9 @@ (define_predicate "local_symbolic_operand" if (TARGET_DLLIMPORT_DECL_ATTRIBUTES && SYMBOL_REF_DLLIMPORT_P (op)) return false; if (SYMBOL_REF_LOCAL_P (op)) - return true; + /* ifuncname@GOTOFF was rejected by the x86 linker before May + 2018, and silently generated wrong code for PIE afterwards. */ + return !ix86_call_use_plt_p (op); /* There is, however, a not insubstantial body of code in the rest of the compiler that assumes it can just stick the results of diff --git a/gcc/testsuite/gcc.target/i386/pr83782-1.c b/gcc/testsuite/gcc.target/i386/pr83782-1.c index ce97b12e65d58..af52278ec4df2 100644 --- a/gcc/testsuite/gcc.target/i386/pr83782-1.c +++ b/gcc/testsuite/gcc.target/i386/pr83782-1.c @@ -20,7 +20,7 @@ bar(void) return foo; } -/* { dg-final { scan-assembler {leal[ \t]foo@GOTOFF\(%[^,]*\),[ \t]%eax} { target ia32 } } } */ +/* { dg-final { scan-assembler-not {leal[ \t]foo@GOTOFF\(%[^,]*\),[ \t]%eax} { target ia32 } } } */ /* { dg-final { scan-assembler {lea(?:l|q)[ \t]foo\(%rip\),[ \t]%(?:e|r)ax} { target { ! ia32 } } } } */ -/* { dg-final { scan-assembler-not "foo@GOT\\\(" { target ia32 } } } */ +/* { dg-final { scan-assembler "foo@GOT\\\(" { target ia32 } } } */ /* { dg-final { scan-assembler-not "foo@GOTPCREL\\\(" { target { ! ia32 } } } } */ diff --git a/gcc/testsuite/gcc.target/i386/pr83782-2.c b/gcc/testsuite/gcc.target/i386/pr83782-2.c index e25d258bbda43..15c7dc04e88c3 100644 --- a/gcc/testsuite/gcc.target/i386/pr83782-2.c +++ b/gcc/testsuite/gcc.target/i386/pr83782-2.c @@ -20,7 +20,7 @@ bar(void) return foo; } -/* { dg-final { scan-assembler {leal[ \t]foo@GOTOFF\(%[^,]*\),[ \t]%eax} { target ia32 } } } */ +/* { dg-final { scan-assembler-not {leal[ \t]foo@GOTOFF\(%[^,]*\),[ \t]%eax} { target ia32 } } } */ /* { dg-final { scan-assembler {lea(?:l|q)[ \t]foo\(%rip\),[ \t]%(?:e|r)ax} { target { ! ia32 } } } } */ -/* { dg-final { scan-assembler-not "foo@GOT\\\(" { target ia32 } } } */ +/* { dg-final { scan-assembler "foo@GOT\\\(" { target ia32 } } } */ /* { dg-final { scan-assembler-not "foo@GOTPCREL\\\(" { target { ! ia32 } } } } */ -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer Disinformation flourishes because many people care deeply about injustice but very few check the facts. 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