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* [glibc/azanella/posix_spawn-clone3] Linux: Do not align the stack for __clone3
@ 2022-11-29 21:21 Adhemerval Zanella
0 siblings, 0 replies; only message in thread
From: Adhemerval Zanella @ 2022-11-29 21:21 UTC (permalink / raw)
To: glibc-cvs
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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