[v2,03/11] Linux: Do not align the stack for __clone3

Message ID 20221104190112.2566409-4-adhemerval.zanella@linaro.org
State New
Headers
Series Optimize posix_spawn signal setup with clone3 |

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Adhemerval Zanella Netto Nov. 4, 2022, 7:01 p.m. UTC
  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.
---
 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
  

Patch

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.  */