Re: [RFC bpf-next v1 8/8] selftests/bpf: test no_caller_saved_registers spill/fill removal

Andrii Nakryiko
2024-07-02T21:21:10Z

On Tue, Jul 2, 2024 at 2:12 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>
> On Mon, 2024-07-01 at 17:42 -0700, Andrii Nakryiko wrote:
>
> [...]
>
> > You don't seem to have a case where offset is not a multiple of 8
> > (though it would have to be a sub-register spill which would be
> > "rejected" anyway, so not sure if there is anything to add here)
>
> My bad, will add such a test-case.
>
> >
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
>
> [...]
>
> > > +void test_verifier_nocsr(void)
> > > +{
> > > +#if defined(__x86_64__)
> > > + RUN(verifier_nocsr);
> > > +#endif /* __x86_64__ */
> >
> > maybe #else <mark-as-skipped> ?
>
> Right, makes sense.
>
> [...]
>
> > > +++ b/tools/testing/selftests/bpf/progs/verifier_nocsr.c
> > > @@ -0,0 +1,437 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +
> > > +#include <linux/bpf.h>
> > > +#include <bpf/bpf_helpers.h>
> > > +#include "bpf_misc.h"
> > > +
> > > +#define __xlated_bpf_get_smp_processor_id \
> > > + __xlated(": w0 = ") \
> >
> > how will this work for no_alu32 mode?
>
> The patch is applied by kernel, and it does not care about alu32
> compiler flags:
>
> insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);

ah, right-right, of course!

> insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
>
> …