Re: RTM instruction compile failure for XABORT when AVX is active

[Roman Dementiev <roman.dementiev@intel.com>]

Hello Thomas,

Sunday, June 28, 2015, 9:38:14 PM, you wrote:

> 2015-06-28 10:59, Matthew Hall:
>> It would appear there is some bug in the new lock elision patches that is preventing it from compiling with clang. Any suggestions?

> It builds with clang.
> My suggestion is to add the patch author in recipient's list ;)


>> On Jun 28, 2015, at 10:16 AM, Matthew Hall <mhall@mhcomputing.net> wrote:
>> 
>> > Hi all,
>> > 
>> > I am getting a strange error compiling some RTM instructions when I upgraded my VM environment from VirtualBox 4 to VirtualBox 5 and AVX instructions from the host CPU became available. However when I am reading the opcode description for XABORT it supposedly allows an immediate operand for the argument so I can't understand why this code would not compile. Any advice?
>> > 
>> >  CC test_hash_scaling.o
>> > In file included from /vagrant/external/dpdk/app/test/test_hash_scaling.c:37:
>> > In file included from /vagrant/external/dpdk/build/include/rte_spinlock.h:42:
>> > /vagrant/external/dpdk/build/include/rte_rtm.h:56:15: error: invalid operand for inline asm constraint 'i'
>> >        asm volatile(".byte 0xc6,0xf8,%P0" :: "i" (status) : "memory");
>> > 
>> > Matthew.
>> 

It  looks  like  a  compiler  bug for me. In the meantime Clang should
have native TSX intrinsics (but    most   compilers   fail   to   implement
them correctly  on  a first attempt allowing instruction reordering). Could
you try this workaround:

diff --git a/lib/librte_eal/common/include/arch/x86/rte_rtm.h b/lib/librte_eal/common/include/arch/x86/rte_rtm.h
index d935641..ee73dd4 100644
--- a/lib/librte_eal/common/include/arch/x86/rte_rtm.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_rtm.h
@@ -50,10 +50,14 @@ void rte_xend(void)
         asm volatile(".byte 0x0f,0x01,0xd5" ::: "memory");
 }

+#include <immintrin.h>
+
 static __attribute__((__always_inline__)) inline
 void rte_xabort(const unsigned int status)
 {
-       asm volatile(".byte 0xc6,0xf8,%P0" :: "i" (status) : "memory");
+       asm volatile(::: "memory");
+       _xabort(status);
+       asm volatile(::: "memory");
 }

 static __attribute__((__always_inline__)) inline


-- 
Best regards,
 Roman                            mailto:roman.dementiev@intel.com

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