On 9/2/2017 4:53 PM, Thomas Monjalon wrote:
2016-11-06 22:09, Thomas Monjalon:
2016-09-29 18:34, Thomas Monjalon:
2016-09-30 02:54, Nikhil Rao:
The original code used movl instead of xchgl, this caused
rte_atomic64_cmpset to use ebx as the lower dword of the source
to cmpxchg8b instead of the lower dword of function argument "src".
Could you please start the explanation with a statement of
what is wrong from an user point of view?
It could help to understand how severe it is.
Please, we need a clear explanation of the bug, and an acknowledgement.
Should we close this bug?
I took a few minutes to look at this, and the issue can easily be
reproduced with a small snippet of code.
With the 'mov', the lower dword of the result is incorrect. This is
resolved by using 'xchgl'.
void main()
{
uint64_t a = 0xff000000ff;
rte_atomic64_cmpset( &a, 0xff000000ff, 0xfa000000fa);
printf("0x%lx\n", a);
}
When using 'mov', the result is 0xfa00000000
When using 'xchgl', the result is 0xfa000000fa, as expected.
Rgds,
Dave.
