[PATCH v4 3/6] Linux: Do not align the stack for __clone3

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

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.

Checked on x86_64-linux-gnu.
---
 include/clone_internal.h                      |  3 +
 .../sysv/linux/tst-misalign-clone-internal.c  | 74 -------------------
 sysdeps/unix/sysv/linux/x86_64/clone3.S       |  3 -
 3 files changed, 3 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..f8198d8059 100644
--- a/include/clone_internal.h
+++ b/include/clone_internal.h
@@ -11,6 +11,9 @@
    Different than kernel, the implementation also returns EINVAL for an
    invalid NULL __CL_ARGS or __FUNC (similar to __clone).
 
+   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 8b94a74819..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) 2021-2023 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 bd4a834e46..802d56cbac 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.  */
-- 
2.34.1