RE: [PATCH 1/3] bpf: fix signed shift overflows in ARM JIT

[Marat Khalili <marat.khalili@huawei.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Tuesday 11 November 2025 16:31
> To: Marat Khalili <marat.khalili@huawei.com>
> Cc: Konstantin Ananyev <konstantin.ananyev@huawei.com>; Stephen Hemminger <stephen@networkplumber.org>;
> dev@dpdk.org
> Subject: Re: [PATCH 1/3] bpf: fix signed shift overflows in ARM JIT
> 
> On Tue, Nov 11, 2025 at 3:40 PM Marat Khalili <marat.khalili@huawei.com> wrote:
> >
> > > On Mon, Nov 10, 2025 at 9:01 PM Marat Khalili <marat.khalili@huawei.com> wrote:
> > > >
> > > > Left shifts of integer literals and bool values overwriting the sign bit
> > > > were used multiple times in bpf_jit_arm64.c. E.g.:
> > > >
> > > >     insn = (!!is64) << 31;
> > > >
> > > > where is64 has type bool (double bang is a no-op here). The operand of
> > > > left shift was promoted to type int, which when 32-bit wide cannot
> > > > represent the result. Similarly literal integers have int type by
> > > > default.  Sanitizer produced the following diagnostic during runtime
> > > > (for various lines):
> > > >
> > > >     lib/bpf/bpf_jit_arm64.c:241:18: runtime error: left shift of 1 by 31
> > > >     places cannot be represented in type 'int'
> > >
> > > Wonder why none of the tests in app/test/test_bpf.c able to catch
> > > this? The generated ARM opcode looks OK (otherwise tests wont pass).
> > > Could you check what is missing in the app/test/test_bpf.c?
> >
> > That tests do trigger it.
> >
> > RTE>>bpf_autotest
> > ../../src/lib/bpf/bpf_jit_arm64.c:320:18: runtime error: left shift of 1 by 31 places cannot be
> represented in type 'int'
> 
> This is when ASAN is enabled. Right?

More likely UBSAN, but yes.

> Is it really generating BAD
> opcode(i.e emiter generating bad OPcode) and test fails?

If allowed to finish the test does not fail.
However, I have not compared DPDK or JIT compiled code with and without changes.