[PATCH] nptl: Remove MULTI_PAGE_ALIASING [BZ #23554]

[PATCH] nptl: Remove MULTI_PAGE_ALIASING [BZ #23554]

[H.J. Lu]

MULTI_PAGE_ALIASING was introduced to mitigate an aliasing issue on
Pentium 4.  It is no longer needed for processors after Pentium 4.
---
 nptl/allocatestack.c               | 10 ----------
 nptl/stack-aliasing.h              | 23 -----------------------
 sysdeps/i386/i686/stack-aliasing.h | 23 -----------------------
 sysdeps/x86_64/stack-aliasing.h    |  1 -
 4 files changed, 57 deletions(-)
 delete mode 100644 nptl/stack-aliasing.h
 delete mode 100644 sysdeps/i386/i686/stack-aliasing.h
 delete mode 100644 sysdeps/x86_64/stack-aliasing.h

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 149b999603..00fddbd409 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -31,7 +31,6 @@
 #include <lowlevellock.h>
 #include <futex-internal.h>
 #include <kernel-features.h>
-#include <stack-aliasing.h>
 
 
 #ifndef NEED_SEPARATE_REGISTER_STACK
@@ -547,15 +546,6 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
       pd = get_cached_stack (&size, &mem);
       if (pd == NULL)
 	{
-	  /* To avoid aliasing effects on a larger scale than pages we
-	     adjust the allocated stack size if necessary.  This way
-	     allocations directly following each other will not have
-	     aliasing problems.  */
-#if MULTI_PAGE_ALIASING != 0
-	  if ((size % MULTI_PAGE_ALIASING) == 0)
-	    size += pagesize_m1 + 1;
-#endif
-
 	  /* If a guard page is required, avoid committing memory by first
 	     allocate with PROT_NONE and then reserve with required permission
 	     excluding the guard page.  */
diff --git a/nptl/stack-aliasing.h b/nptl/stack-aliasing.h
deleted file mode 100644
index bfdde53e53..0000000000
--- a/nptl/stack-aliasing.h
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Define macros for stack address aliasing issues for NPTL.  Stub version.
-   Copyright (C) 2014-2021 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/>.  */
-
-/* This is a number of bytes that is an alignment that should be avoided
-   when choosing the exact size of a new thread's stack.  If the size
-   chosen is aligned to this, an extra page will be added to render the
-   size off-aligned.  */
-#define MULTI_PAGE_ALIASING     0
diff --git a/sysdeps/i386/i686/stack-aliasing.h b/sysdeps/i386/i686/stack-aliasing.h
deleted file mode 100644
index d521dcdb75..0000000000
--- a/sysdeps/i386/i686/stack-aliasing.h
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Define macros for stack address aliasing issues for NPTL.  i686 version.
-   Copyright (C) 2014-2021 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/>.  */
-
-/* What is useful is to avoid the 64k aliasing problem which reliably
-   happens if all stacks use sizes which are a multiple of 64k.  Tell
-   the stack allocator to disturb this by allocation one more page if
-   necessary.  */
-#define MULTI_PAGE_ALIASING     65536
diff --git a/sysdeps/x86_64/stack-aliasing.h b/sysdeps/x86_64/stack-aliasing.h
deleted file mode 100644
index 2efdacb3b4..0000000000
--- a/sysdeps/x86_64/stack-aliasing.h
+++ /dev/null
@@ -1 +0,0 @@
-#include <sysdeps/i386/i686/stack-aliasing.h>
-- 
2.30.2

Re: [PATCH] nptl: Remove MULTI_PAGE_ALIASING [BZ #23554]

[Florian Weimer]

* H. J. Lu via Libc-alpha:

> MULTI_PAGE_ALIASING was introduced to mitigate an aliasing issue on
> Pentium 4.  It is no longer needed for processors after Pentium 4.

Thanks, looks okay.