Apologies if this is an inappropriate forum for this question, but we're
wondering if anyone else has run into this behavior on a DM6446 using
gcc/g++.
We've been getting disappointing performance with our DM6446
application, and have been running OProfile in an attempt to root up
bottlenecks. While doing so, we noticed do_fpe() and other associated
NWFPE floating point emulation calls were topping out the symbol list in
opreport. We stripped all of the floating point operations out of the
application, and yet the NWFPE symbols persisted in the opreport. In an
attempt to narrow the location of the offending code, we noticed that if
we stripped out things that dealt with C++ std::string, the NWFPE calls
disappeared!
Perplexed, we wrote a Hello World! app:
//////////////////////////////////////////
#include <iostream>
using namespace std;
int main()
{
while(1)
{
cout << "Hello World!";
}
return EXIT_SUCCESS;
}
//////////////////////////////////////////
Only to find, that when profiling this app, the NWFPE calls were at the
top of the opreport (all told, about 25% of snapshots were taken from
within some part of the NWFPE in the kernel)! We then replaced the
'cout' line with:
int i=i+1;
The NWFPE calls disappeared. Replacing 'cout' with 'printf' also
prevents the NWFPE symbols from showing up in an opreport. Surely the
code for 'cout << "Hello World!"' doesn't cause floating point
instructions to be emitted... right? This issue appeared in our main
app when C++ strings were constructed, as well. Objdump does not reveal
any floating point instructions that I can see.
This happens regardless of optimization settings.
Has anyone run into a similar phenomenon? We're really scratching our
heads on this one.
arm-linux-gcc version 3.4.6 glibc-2.3.6 built by a 3rd party using
crosstool-0.42, Linux 2.6.18. We are using hardware floating point
emulation since that's what was provided to us by our 3rd party LSP, but
we're in the process of building our own soft-float toolchain (that's
another story...). Regardless, these calls shouldn't be showing up the
way they are...
Any insight sincerely appreciated,
Ryan
////////////////////////////////////////////////////////////////////////
//////////////
Ryan Talbot
Instrumentation Engineer
Virginia Tech Transportation Institute
3500 Transportation Research Plaza
Blacksburg, VA 24061
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