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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 ED753C3B1B7 for ; Fri, 14 Feb 2020 18:18:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C21082168B for ; Fri, 14 Feb 2020 18:18:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581704302; bh=ERfQ3eAbohrmh759MhxBh8l+4EKx0sFujaFwkM2jL3g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=C+/l18cToQRajZjRD0SOCJBW64J4DlADUT/0TBOLFoHPCNTgpTpGEfPs/OP8xN6fP iPXezexj3Q8/lsnufIl/Bc/JpUy162gpRCqGRpc5sJY5Dd/0WbKiGib6m/V7ILnabb P5R3Jz5G0MPE/KXoX/DHFq9ttdzg3cC1eGOg/DwY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730592AbgBNPut (ORCPT ); Fri, 14 Feb 2020 10:50:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:54966 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730555AbgBNPul (ORCPT ); Fri, 14 Feb 2020 10:50:41 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 58C0D2467E; Fri, 14 Feb 2020 15:50:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581695440; bh=ERfQ3eAbohrmh759MhxBh8l+4EKx0sFujaFwkM2jL3g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J8jEdBgmBZeh3KNLNaX/BSAFHJuISr9VUNgeqjgzw6DznjKp/0U6CXgemgPt5KOJK zcx70d/bOGs57ipvq0glbEeceZMm9djERoR8IyhL953FXbakRNt9i9BAjBy3Q3IcX/ Lm6ZnSMcAYUWgcTXtuJ+b2mMD/hc7tel0oC6x2xw= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Siddhesh Poyarekar , Masami Hiramatsu , Tim Bird , Shuah Khan , Sasha Levin , linux-kselftest@vger.kernel.org Subject: [PATCH AUTOSEL 5.5 081/542] kselftest: Minimise dependency of get_size on C library interfaces Date: Fri, 14 Feb 2020 10:41:13 -0500 Message-Id: <20200214154854.6746-81-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200214154854.6746-1-sashal@kernel.org> References: <20200214154854.6746-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Siddhesh Poyarekar [ Upstream commit 6b64a650f0b2ae3940698f401732988699eecf7a ] 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=5479 Signed-off-by: Siddhesh Poyarekar Reported-by: Masami Hiramatsu Tested-by: Masami Hiramatsu Reviewed-by: Tim Bird Signed-off-by: Shuah Khan Signed-off-by: Sasha Levin --- 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/selftests/size/get_size.c index 2ad45b9443550..2980b1a63366b 100644 --- a/tools/testing/selftests/size/get_size.c +++ b/tools/testing/selftests/size/get_size.c @@ -11,23 +11,35 @@ * 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. */ #include #include +#include #define STDOUT_FILENO 1 static int print(const char *s) { - return write(STDOUT_FILENO, s, __builtin_strlen(s)); + size_t len = 0; + + while (s[len] != '\0') + len++; + + return syscall(SYS_write, STDOUT_FILENO, s, len); } static inline char *num_to_str(unsigned long num, char *buf, int len) @@ -79,12 +91,12 @@ void _start(void) print("TAP version 13\n"); print("# Testing system size.\n"); - ccode = sysinfo(&info); + ccode = 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); @@ -100,5 +112,5 @@ void _start(void) print(" ...\n"); print("1..1\n"); - _exit(0); + syscall(SYS_exit, 0); } -- 2.20.1