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3a22d332c7
Bug#52261: 64 bit atomic operations do not work on Solaris i386
gcc in debug compilation
One of the various problems was that the source operand to
CMPXCHG8b was marked as a input/output operand, causing GCC
to use the EBX register as the destination register for the
CMPXCHG8b instruction. This could lead to crashes as the EBX
register is also implicitly used by the instruction, causing
the value to be potentially garbaged and a protection fault
once the value is used to access a position in memory.
Another problem was the lack of proper clobbers for the atomic
operations and, also, a discrepancy between the implementations
for the Compare and Set operation. The specific problems are
described and fixed by Kristian Nielsen patches:
Patch: 1
Fix bugs in my_atomic_cas*(val,cmp,new) that *cmp is accessed
after CAS succeds.
In the gcc builtin implementation, problem was that *cmp was
read again after atomic CAS to check if old *val == *cmp;
this fails if CAS is successful and another thread modifies
*cmp in-between.
In the x86-gcc implementation, problem was that *cmp was set
also in the case of successful CAS; this means there is a
window where it can clobber a value written by another thread
after successful CAS.
Patch 2:
Add a GCC asm "memory" clobber to primitives that imply a
memory barrier.
This signifies to GCC that any potentially aliased memory
must be flushed before the operation, and re-read after the
operation, so that read or modification in other threads of
such memory values will work as intended.
In effect, it makes these primitives work as memory barriers
for the compiler as well as the CPU. This is better and more
correct than adding "volatile" to variables.
42 lines
1.6 KiB
C
42 lines
1.6 KiB
C
#ifndef ATOMIC_GCC_BUILTINS_INCLUDED
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#define ATOMIC_GCC_BUILTINS_INCLUDED
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/* Copyright (C) 2008 MySQL AB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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#define make_atomic_add_body(S) \
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v= __sync_fetch_and_add(a, v);
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#define make_atomic_fas_body(S) \
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v= __sync_lock_test_and_set(a, v);
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#define make_atomic_cas_body(S) \
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int ## S sav; \
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int ## S cmp_val= *cmp; \
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sav= __sync_val_compare_and_swap(a, cmp_val, set);\
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if (!(ret= (sav == cmp_val))) *cmp= sav
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#ifdef MY_ATOMIC_MODE_DUMMY
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#define make_atomic_load_body(S) ret= *a
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#define make_atomic_store_body(S) *a= v
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#define MY_ATOMIC_MODE "gcc-builtins-up"
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#else
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#define MY_ATOMIC_MODE "gcc-builtins-smp"
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#define make_atomic_load_body(S) \
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ret= __sync_fetch_and_or(a, 0);
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#define make_atomic_store_body(S) \
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(void) __sync_lock_test_and_set(a, v);
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#endif
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#endif /* ATOMIC_GCC_BUILTINS_INCLUDED */
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