fabian.hachenberg@… — Thu, 04 Dec 2014 18:23:51 GMT

Sorry for the messup of code blocks.

Here's the original code

inline int atomic_exchange_and_add( int * pw, int dv )
{
    // int r = *pw;
    // *pw += dv;
    // return r;
    int r;
    __asm__ __volatile__
    (
        "lock\n\t"
        "xadd %1, %0":
        "=m"( *pw ), "=r"( r ): // outputs (%0, %1)
        "m"( *pw ), "1"( dv ): // inputs (%2, %3 == %1)
        "memory", "cc" // clobbers
    );
    return r;
}

Here's the patches version

inline int atomic_exchange_and_add( int * pw, int dv )
{
    // int r = *pw;
    // *pw += dv;
    // return r;
    __asm__ __volatile__
    (
        "lock\n\t"
        "xadd %1, %0":
        "+m"( *pw ), "+r"( dv ): // input/output (%0, %1)
                :
        "memory", "cc" // clobbers
    );
    return dv;
}

Boost C++ Libraries: Ticket #10850: gcc-x86-implementation of "atomic_exchange_and_add" triggers intel's "unitialized variable" runtime check