From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78A62C33CAF for ; Mon, 13 Jan 2020 16:43:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DC0B20678 for ; Mon, 13 Jan 2020 16:43:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=gotplt.org header.i=@gotplt.org header.b="jnHEh8wh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728829AbgAMQnZ (ORCPT ); Mon, 13 Jan 2020 11:43:25 -0500 Received: from bonobo.elm.relay.mailchannels.net ([23.83.212.22]:26288 "EHLO bonobo.elm.relay.mailchannels.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726567AbgAMQnY (ORCPT ); Mon, 13 Jan 2020 11:43:24 -0500 X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id 883BA3C1610; Mon, 13 Jan 2020 16:43:22 +0000 (UTC) Received: from pdx1-sub0-mail-a88.g.dreamhost.com (100-96-6-15.trex.outbound.svc.cluster.local [100.96.6.15]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id 56B763C16D5; Mon, 13 Jan 2020 16:43:21 +0000 (UTC) X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from pdx1-sub0-mail-a88.g.dreamhost.com ([TEMPUNAVAIL]. [64.90.62.162]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384) by 0.0.0.0:2500 (trex/5.18.5); Mon, 13 Jan 2020 16:43:22 +0000 X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|siddhesh@gotplt.org X-MailChannels-Auth-Id: dreamhost X-Keen-Stretch: 3235dbbf22ea3696_1578933801931_2886516590 X-MC-Loop-Signature: 1578933801930:4209032477 X-MC-Ingress-Time: 1578933801929 Received: from pdx1-sub0-mail-a88.g.dreamhost.com (localhost [127.0.0.1]) by pdx1-sub0-mail-a88.g.dreamhost.com (Postfix) with ESMTP id 68405804B1; Mon, 13 Jan 2020 08:43:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=gotplt.org; h=from:to:cc :subject:date:message-id:mime-version:content-transfer-encoding; s=gotplt.org; bh=cD2vVZ2ZPP1g0U3aa4tqp4qDQSc=; b=jnHEh8whc1Z/n/ L0df/B8iUhfgav37u3J/myrP1pw6td+64j9GQ8PBidyp5+6hWJ/IvVc9/aXIKmr7 NOEkM/SZ/Kq+ret99VzpEFq301m8TSYBxQzqDyDfxGxM1XYdTzx7uiR/WuXR4omq 7bqVAEAYfND2KF74vAZmavrlJ756g= Received: from linaro-laptop.intra.reserved-bit.com (unknown [123.252.202.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: siddhesh@gotplt.org) by pdx1-sub0-mail-a88.g.dreamhost.com (Postfix) with ESMTPSA id 26CCC804B3; Mon, 13 Jan 2020 08:43:07 -0800 (PST) X-DH-BACKEND: pdx1-sub0-mail-a88 From: Siddhesh Poyarekar To: linux-kselftest@vger.kernel.org Cc: Shuah Khan , linux-kernel@vger.kernel.org, Siddhesh Poyarekar , Masami Hiramatsu Subject: [PATCH] kselftest: Minimise dependency of get_size on C library interfaces Date: Mon, 13 Jan 2020 22:11:58 +0530 Message-Id: <20200113164158.15803-1-siddhesh@gotplt.org> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 X-VR-OUT-STATUS: OK X-VR-OUT-SCORE: -100 X-VR-OUT-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedufedrvdejtddgledtucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuggftfghnshhusghstghrihgsvgdpffftgfetoffjqffuvfenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhephffvufffkffoggfgsedtkeertdertddtnecuhfhrohhmpefuihguughhvghshhcurfhohigrrhgvkhgrrhcuoehsihguughhvghshhesghhothhplhhtrdhorhhgqeenucffohhmrghinheplhhinhgrrhhordhorhhgnecukfhppeduvdefrddvhedvrddvtddvrddujedvnecurfgrrhgrmhepmhhouggvpehsmhhtphdphhgvlhhopehlihhnrghrohdqlhgrphhtohhprdhinhhtrhgrrdhrvghsvghrvhgvugdqsghithdrtghomhdpihhnvghtpeduvdefrddvhedvrddvtddvrddujedvpdhrvghtuhhrnhdqphgrthhhpefuihguughhvghshhcurfhohigrrhgvkhgrrhcuoehsihguughhvghshhesghhothhplhhtrdhorhhgqedpmhgrihhlfhhrohhmpehsihguughhvghshhesghhothhplhhtrdhorhhgpdhnrhgtphhtthhopehmrghsrghmihdrhhhirhgrmhgrthhsuheslhhinhgrrhhordhorhhgnecuvehluhhsthgvrhfuihiivgeptd Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was observed[1] on arm64 that __builtin_strlen led to an infinite loop in the get_size selftest. This is because __builtin_strlen (and other builtins) may sometimes result in a call to the C library function. The C library implementation of strlen uses an IFUNC resolver to load the most efficient strlen implementation for the underlying machine and hence has a PLT indirection even for static binaries. Because this binary avoids the C library startup routines, the PLT initialization never happens and hence the program gets stuck in an infinite loop. On x86_64 the __builtin_strlen just happens to expand inline and avoid the call but that is not always guaranteed. Further, while testing on x86_64 (Fedora 31), it was observed that the test also failed with a segfault inside write() because the generated code for the write function in glibc seems to access TLS before the syscall (probably due to the cancellation point check) and fails because TLS is not initialised. To mitigate these problems, this patch reduces the interface with the C library to just the syscall function. The syscall function still sets errno on failure, which is undesirable but for now it only affects cases where syscalls fail. [1] https://bugs.linaro.org/show_bug.cgi?id=3D5479 Signed-off-by: Siddhesh Poyarekar Reported-by: Masami Hiramatsu --- tools/testing/selftests/size/get_size.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/tools/testing/selftests/size/get_size.c b/tools/testing/self= tests/size/get_size.c index d4b59ab979a0..f55943b6d1e2 100644 --- a/tools/testing/selftests/size/get_size.c +++ b/tools/testing/selftests/size/get_size.c @@ -12,23 +12,35 @@ * own execution. It also attempts to have as few dependencies * on kernel features as possible. * - * It should be statically linked, with startup libs avoided. - * It uses no library calls, and only the following 3 syscalls: + * It should be statically linked, with startup libs avoided. It uses + * no library calls except the syscall() function for the following 3 + * syscalls: * sysinfo(), write(), and _exit() * * For output, it avoids printf (which in some C libraries * has large external dependencies) by implementing it's own * number output and print routines, and using __builtin_strlen() + * + * The test may crash if any of the above syscalls fails because in some + * libc implementations (e.g. the GNU C Library) errno is saved in + * thread-local storage, which does not get initialized due to avoiding + * startup libs. */ =20 #include #include +#include =20 #define STDOUT_FILENO 1 =20 static int print(const char *s) { - return write(STDOUT_FILENO, s, __builtin_strlen(s)); + size_t len =3D 0; + + while (s[len] !=3D '\0') + len++; + + return syscall(SYS_write, STDOUT_FILENO, s, len); } =20 static inline char *num_to_str(unsigned long num, char *buf, int len) @@ -80,12 +92,12 @@ void _start(void) print("TAP version 13\n"); print("# Testing system size.\n"); =20 - ccode =3D sysinfo(&info); + ccode =3D syscall(SYS_sysinfo, &info); if (ccode < 0) { print("not ok 1"); print(test_name); print(" ---\n reason: \"could not get sysinfo\"\n ...\n"); - _exit(ccode); + syscall(SYS_exit, ccode); } print("ok 1"); print(test_name); @@ -101,5 +113,5 @@ void _start(void) print(" ...\n"); print("1..1\n"); =20 - _exit(0); + syscall(SYS_exit, 0); } --=20 2.24.1