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Re: libsanitizer merge from upstream r208536

On Fri, May 23, 2014 at 01:54:47PM -0500, Peter Bergner wrote:
> On Fri, 2014-05-23 at 11:47 -0500, Peter Bergner wrote:
> > The following patch gets bootstrap working again, but there seems to
> > be a large number of testsuite failures I will look into before
> > submitting the patch to the LLVM mailing list.
> FYI, it looks like a huge number of the failures are from the following
> in 32-bit mode:
> /home/bergner/gcc/build/gcc-fsf-mainline-asan-debug/powerpc64-linux/32/libsanitizer/asan/.libs/ undefined reference to `__sync_fetch_and_add_8'^M
> collect2: error: ld returned 1 exit status^M
> Kosta, we don't have a __sync_fetch_and_add_8 in 32-bit, since
> we don't have the necessary hardware instructions to do a 64-bit
> fetch and add.  How is this supposed to work?  There are some
> libatomic routines we could call (eg, __atomic_fetch_add_8).

But libatomic in the end for that cases uses locking and non-atomic access
anyway.  On i?86 64-bit atomics are available starting with i586,
on sparc starting with v9, but I believe on most architectures
if you have atomics at all you don't have atomics larger than word size.

For GCC, if you want in the preprocessor to test if a CPU has 64-bit
atomics, you'd check #ifdef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8
Can you use locking instead otherwise?


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