[dpdk-dev] eal: fix c++ compilation issue with rte_delay_us()

  When compiling with C++, it treats
void (*rte_delay_us)(unsigned int us);
as definition of the global variable.
So further linking with librte_eal fails.

Fixes: b4d63fb62240 ("eal: customize delay function")

Steps to reproduce:

$ cat rttm1.cpp

#include <iostream>
#include <rte_eal.h>
#include <rte_cycles.h>

using namespace std;

int main(int argc, char *argv[])
{
        int ret = rte_eal_init(argc, argv);
        rte_delay_us(1);
        cout << "return code ";
        cout << ret;
        return ret;
}

$ g++ -m64 -I/${RTE_SDK}/${RTE_TARGET}/include -c  -o rttm1.o rttm1.cpp
$ gcc -m64 -pthread -o rttm1 rttm1.o -ldl -Wl,-lstdc++ \
  -L/${RTE_SDK}/${RTE_TARGET}/lib -Wl,-lrte_eal
.../librte_eal.a(eal_common_timer.o):
(.bss+0x0): multiple definition of `rte_delay_us'
rttm1.o:(.bss+0x0): first defined here
collect2: error: ld returned 1 exit status

$ nm rttm1.o | grep rte_delay_us
0000000000000092 t _GLOBAL__sub_I_rte_delay_us
0000000000000000 B rte_delay_us


Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
---
 lib/librte_eal/common/include/generic/rte_cycles.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

2016-10-03 18:27, Konstantin Ananyev:
> When compiling with C++, it treats
> void (*rte_delay_us)(unsigned int us);
> as definition of the global variable.
> So further linking with librte_eal fails.
> 
> Fixes: b4d63fb62240 ("eal: customize delay function")

Applied, thanks

I don't understand why it was not failing with C compilation?
  

Hi Thomas,

> 
> 2016-10-03 18:27, Konstantin Ananyev:
> > When compiling with C++, it treats
> > void (*rte_delay_us)(unsigned int us);
> > as definition of the global variable.
> > So further linking with librte_eal fails.
> >
> > Fixes: b4d63fb62240 ("eal: customize delay function")
> 
> Applied, thanks
> 
> I don't understand why it was not failing with C compilation?

Don't know off hand.
Yes, I would expect gcc to fail with same symptoms too.
But by some reason it puts it makes it a 'common' symbol:

$ cat rttm1.c

#include <stdio.h>
#include <rte_eal.h>
#include <rte_cycles.h>

int main(int argc, char *argv[])
{
        int ret = rte_eal_init(argc, argv);
        rte_delay_us(1);
        printf("return code: %d\n", ret);
        return ret;
}

$ gcc -m64 -pthread -o rttm1 rttm1.o -ldl   -L/${RTE_SDK}/${RTE_TARGET}/lib -Wl,-lrte_eal
$ nm rttm1.o | grep rte_delay_us
0000000000000008 C rte_delay_us

Konstantin