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/* Copyright (C) 2010, 2011 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
This file is part of the GNU Transactional Memory Library (libitm).
Libitm is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
Libitm 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 General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#include "libitm_i.h"
namespace GTM HIDDEN {
// Filter out any updates that overlap the libitm stack, as defined by
// TOP (entry point to library) and BOT (below current function). This
// definition should be fine for all stack-grows-down architectures.
gtm_cacheline_mask __attribute__((noinline))
gtm_mask_stack(gtm_cacheline *line, gtm_cacheline_mask mask)
{
void *top = gtm_thr()->jb.cfa;
void *bot = __builtin_dwarf_cfa();
// We must have come through an entry point that set TOP.
assert (top != NULL);
if (line + 1 < bot)
{
// Since we don't have the REAL stack boundaries for this thread,
// we cannot know if this is a dead write to a stack address below
// the current function or if it is write to another VMA. In either
// case allowing the write should not affect correctness.
}
else if (line >= top)
{
// A valid write to an address in an outer stack frame, or a write
// to another VMA.
}
else
{
uintptr_t diff = (uintptr_t)top - (uintptr_t)line;
if (diff >= CACHELINE_SIZE)
{
// The write is either fully within the proscribed area, or the tail
// of the cacheline overlaps the proscribed area. Assume that all
// stacks are at least cacheline aligned and declare the head of the
// cacheline dead.
mask = 0;
}
else
{
// The head of the cacheline is within the proscribed area, but the
// tail of the cacheline is live. Eliminate the dead writes.
mask &= (gtm_cacheline_mask)-1 << diff;
}
}
return mask;
}
} // namespace GTM
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