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[192.0.145.146]) by smtp.gmail.com with ESMTPSA id n30-20020a02a19e000000b0039de238deb5sm4802377jah.175.2023.01.11.13.43.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Jan 2023 13:43:27 -0800 (PST) Message-ID: Date: Wed, 11 Jan 2023 16:43:26 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v2 03/11] Linux: Do not align the stack for __clone3 To: Adhemerval Zanella , libc-alpha@sourceware.org, Szabolcs Nagy , "H . J . Lu" Cc: Christian Brauner References: <20221104190112.2566409-1-adhemerval.zanella@linaro.org> <20221104190112.2566409-4-adhemerval.zanella@linaro.org> Organization: Red Hat In-Reply-To: <20221104190112.2566409-4-adhemerval.zanella@linaro.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Carlos O'Donell via Libc-alpha Reply-To: Carlos O'Donell Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" On 11/4/22 15:01, Adhemerval Zanella via Libc-alpha wrote: > Adjusting the stack on child thread is not async-signal safe, since > kernel does not enforce stack alignmnet. Although, all the internal > usage of __clone_internal are done with all signal masked, removing > stack alignment of __clone3 is still a net gain: is simplifies the > function contract detail (mask/unmarsk signals) and simplifies the > arch-specific code. Please post v4. Suggest: All internal callers of __clone3 should provide an already aligned stack. Removing the stack alignment in __clone3 is a net gain: it simplifies the internal function contract (mask/unmask signals) along with the arch-specific code. > > The internal users are responsible for correct stack alignment. If > glibc ever exports a clone3 wrapper, it should adjust stack alignment. > > Checked on x86_64-linux-gnu. > --- > include/clone_internal.h | 5 ++ > .../sysv/linux/tst-misalign-clone-internal.c | 74 ------------------- > sysdeps/unix/sysv/linux/x86_64/clone3.S | 3 - > 3 files changed, 5 insertions(+), 77 deletions(-) > delete mode 100644 sysdeps/unix/sysv/linux/tst-misalign-clone-internal.c > > diff --git a/include/clone_internal.h b/include/clone_internal.h > index 73b8114df4..5a48c7caa5 100644 > --- a/include/clone_internal.h > +++ b/include/clone_internal.h > @@ -11,6 +11,11 @@ > Different than kernel, the implementation also returns EINVAL for an > invalid NULL __CL_ARGS or __FUNC (similar to __clone). > > + The stack is not aligned prior the syscall, different than exported > + __clone. Adjusting the stack on child is not async-signal safe and since > + it is used only internally the caller is responsible for proper stack > + alignment. Suggest: All callers are responsible for correctly aligning the stack. The stack is not aligned prior to the syscall (this differs from the exported __clone). > + > This function is only implemented if the ABI defines HAVE_CLONE3_WRAPPER. > */ > extern int __clone3 (struct clone_args *__cl_args, size_t __size, > diff --git a/sysdeps/unix/sysv/linux/tst-misalign-clone-internal.c b/sysdeps/unix/sysv/linux/tst-misalign-clone-internal.c > deleted file mode 100644 > index e039ca5a3a..0000000000 > --- a/sysdeps/unix/sysv/linux/tst-misalign-clone-internal.c > +++ /dev/null > @@ -1,74 +0,0 @@ > -/* Verify that __clone_internal properly aligns the child stack. > - Copyright (C) 2021-2022 Free Software Foundation, Inc. > - This file is part of the GNU C Library. > - > - The GNU C Library is free software; you can redistribute it and/or > - modify it under the terms of the GNU Lesser General Public > - License as published by the Free Software Foundation; either > - version 2.1 of the License, or (at your option) any later version. > - > - The GNU C Library is distributed in the hope that it will be useful, > - but WITHOUT ANY WARRANTY; without even the implied warranty of > - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > - Lesser General Public License for more details. > - > - You should have received a copy of the GNU Lesser General Public > - License along with the GNU C Library; if not, see > - . */ > - > -#include > -#include > -#include > -#include > -#include > -#include > -#include > -#include > -#include > -#include > -#include > -#include > - > -static int > -check_stack_alignment (void *arg) > -{ > - puts ("in f"); > - > - return TEST_STACK_ALIGN () ? 1 : 0; > -} > - > -static int > -do_test (void) > -{ > - puts ("in do_test"); > - > - if (TEST_STACK_ALIGN ()) > - FAIL_EXIT1 ("stack isn't aligned\n"); > - > -#ifdef __ia64__ > -# define STACK_SIZE (256 * 1024) > -#else > -# define STACK_SIZE (128 * 1024) > -#endif > - char st[STACK_SIZE + 1]; > - /* NB: Align child stack to 1 byte. */ > - char *stack = PTR_ALIGN_UP (&st[0], 2) + 1; > - struct clone_args clone_args = > - { > - .stack = (uintptr_t) stack, > - .stack_size = STACK_SIZE, > - }; > - pid_t p = __clone_internal (&clone_args, check_stack_alignment, 0); > - > - /* Clone must not fail. */ > - TEST_VERIFY_EXIT (p != -1); > - > - int e; > - xwaitpid (p, &e, __WCLONE); > - TEST_VERIFY (WIFEXITED (e)); > - TEST_COMPARE (WEXITSTATUS (e), 0); > - > - return 0; > -} > - > -#include OK. > diff --git a/sysdeps/unix/sysv/linux/x86_64/clone3.S b/sysdeps/unix/sysv/linux/x86_64/clone3.S > index 18fc2ee966..989b62bdf6 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/clone3.S > +++ b/sysdeps/unix/sysv/linux/x86_64/clone3.S > @@ -73,9 +73,6 @@ L(thread_start): > the outermost frame obviously. */ > xorl %ebp, %ebp > > - /* Align stack to 16 bytes per the x86-64 psABI. */ > - and $-16, %RSP_LP OK. > - > /* Set up arguments for the function call. */ > mov %R8_LP, %RDI_LP /* Argument. */ > call *%rdx /* Call function. */ -- Cheers, Carlos.