Re: [dpdk-stable] [PATCH] test/bpf: fix auto-test with clang fails

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 20 Oct 2021 20:46:31 +0200
David Marchand <david.marchand@redhat.com> wrote:

> On Mon, Oct 18, 2021 at 5:59 PM Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> > Konstantin Ananyev <konstantin.ananyev@intel.com> wrote:  
> > > test_shift1_check() function fails with clang build.
> > > The reason for that is that clang uses 64-bit shift instruction for
> > > what expected to be 32-bit operation.
> > > To be more specific, this C code:
> > > r2 = (uint32_t)r2 >> r4;
> > > With clang produces:
> > > 41a4eb:       48 d3 ef                shr    %cl,%rdi
> > > In that particular case it is an allowed choice, as from one side
> > > left-operand value is known to fit into 32 bits, from other side
> > > according to 'C' standard:
> > > "...if the value of the right operand is negative or is greater than
> > > or equal to the width of the promoted left operand, the behavior is
> > > undefined."
> > > The problem is that on x86 behavior for 64-bit and 32-bit shift
> > > operation might differ.
> > > The fix avoids undefined behavior by making sure
> > > that right operand will not exceed width of the promoted left operand.
> > >
> > > Bugzilla ID: 811
> > > Fixes: 9f8f9d91a701 ("test/bpf: introduce functional test")
> > > Cc: stable@dpdk.org
> > >
> > > Reported-by: Stephen Hemminger <stephen@networkplumber.org>
> > > Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>  
> > Acked-by: Stephen Hemminger <stephen@networkplumber.org>  
> 
> Applied, thanks.
> 
> Probably worth adding bpf_autotest in the fast-tests list.
> There are other missing tests in this list, for my todolist unless
> someone wants to look at it.

That is what found this...
https://patchwork.dpdk.org/project/dpdk/patch/20211015201129.63220-11-stephen@networkplumber.org/