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

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 18 Oct 2021 14:40:52 +0100
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>

Thanks

Acked-by: Stephen Hemminger <stephen@networkplumber.org>