On Thu, Apr 4, 2024 at 11:48 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
>
> On 4/2/24 4:26 PM, Andrii Nakryiko wrote:
> > On Tue, Apr 2, 2024 at 3:50 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
> >> Add selftests validating that BPF verifier handles precision marking
> >> for SCALAR registers derived from r10 (fp) register correctly.
> >>
> >> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> >> ---
> >> .../bpf/progs/verifier_subprog_precision.c | 86 +++++++++++++++++++
> >> 1 file changed, 86 insertions(+)
> >>
> >> diff --git a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
> >> index 6f5d19665cf6..e1a8f107f0a7 100644
> >> --- a/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
> >> +++ b/tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
> >> @@ -76,6 +76,92 @@ __naked int subprog_result_precise(void)
> >> );
> >> }
> >>
> >> +__naked __noinline __used
> >> +static unsigned long fp_leaking_subprog()
> >> +{
> >> + asm volatile (
> >> + "r0 = (s8)r10;"
> > Our CI's clang doesn't like this instruction. I guess I'll have to
> > encode it in binary form :(
>
> This patch disappeared from CI so I am not able to check the result.
>
> But I tried with the following small example.
>
> $ cat t.c
> __attribute__((naked)) unsigned long t(void)
> {
> asm volatile("r0 = (s8)r10;"
> "exit;"
> );
> }
>
> $ clang --target=bpf -O2 -mcpu=v2 -g -c t.c && llvm-objdump -d t.o
>
You are using local clang built from source code, right? I think our
BPF CI still is on Clang 17 or something, so it doesn't yet understand
"(s8)r10" syntax, unfortunately.
> t.o: file format elf64-bpf
>
> Disassembly of section .text:
>
> 0000000000000000 <t>:
> 0: bf a0 08 00 00 00 00 00 r0 = (s8)r10
> 1: 95 00 00 00 00 00 00 00 exit
>
>
> -mcpu=v3/v4 has the same result.
> Not sure what clang complains.
>
> >
> >> + "exit;"
> >> + );
> >> +}
> >> +
> > [...]
> >
