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From: Adhemerval Zanella <azanella@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/azanella/posix_spawn-clone3] Linux: Do not align the stack for __clone3 Date: Tue, 29 Nov 2022 21:21:05 +0000 (GMT) [thread overview] Message-ID: <20221129212105.D85A33858D3C@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=298b2da260a70e3bad5668902e1c76b36b47d77e commit 298b2da260a70e3bad5668902e1c76b36b47d77e Author: Adhemerval Zanella <adhemerval.zanella@linaro.org> Date: Fri Nov 4 09:31:01 2022 -0300 Linux: Do not align the stack for __clone3 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. 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. Diff: --- include/clone_internal.h | 5 ++ .../unix/sysv/linux/tst-misalign-clone-internal.c | 74 ---------------------- sysdeps/unix/sysv/linux/x86_64/clone3.S | 3 - 3 files changed, 5 insertions(+), 77 deletions(-) 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. + 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 - <https://www.gnu.org/licenses/>. */ - -#include <sched.h> -#include <stdbool.h> -#include <stdint.h> -#include <stdio.h> -#include <string.h> -#include <sys/wait.h> -#include <unistd.h> -#include <libc-pointer-arith.h> -#include <tst-stack-align.h> -#include <clone_internal.h> -#include <support/xunistd.h> -#include <support/check.h> - -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 <support/test-driver.c> 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 - /* Set up arguments for the function call. */ mov %R8_LP, %RDI_LP /* Argument. */ call *%rdx /* Call function. */
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