Re: [PATCH bpf-next] selftests/bpf: Fix the invalid operand for instruction issue

[Feng Yang]

On Tue, 26 Aug 2025 21:48:43 -0700, Eduard Zingerman <eddy...@gmail.com> wrote:

> On Wed, 2025-08-27 at 11:15 +0800, Feng Yang wrote:
> > From: Feng Yang <yangf...@kylinos.cn>
> > 
> > The following issue occurs when compiling with clang version 17.0.6,
> > but not with version 18.1.8. Add a version restriction to fix this problem.
> > 
> > progs/compute_live_registers.c:251:3: error: invalid operand for instruction
> >   251 |                 "r0 = 1;"
> >       |                 ^
> > <inline asm>:1:22: note: instantiated into assembly here
> >     1 |         r0 = 1;r2 = 2;if r1 & 0x7 goto +1;exit;r0 = r2;exit;
> >       |                             ^
> > 1 error generated.
> > 
> > Fixes: 4a4b84ba9e453 ("selftests/bpf: verify jset handling in CFG 
> > computation")
> > Signed-off-by: Feng Yang <yangf...@kylinos.cn>
> > ---
> >  tools/testing/selftests/bpf/progs/compute_live_registers.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/bpf/progs/compute_live_registers.c 
> > b/tools/testing/selftests/bpf/progs/compute_live_registers.c
> > index 6884ab99a421..56aec43f206f 100644
> > --- a/tools/testing/selftests/bpf/progs/compute_live_registers.c
> > +++ b/tools/testing/selftests/bpf/progs/compute_live_registers.c
> > @@ -240,6 +240,7 @@ __naked void if2(void)
> >             ::: __clobber_all);
> >  }
> >  
> > +#if __clang_major__ >= 18

> Instead of guarding this with compiler version, could you please use
> progs/bpf_misc.h:__imm_insn() macro for the jset instruction?

I don't know much about assembly language. Could you tell me if the following 
changes are correct?

diff --git a/tools/testing/selftests/bpf/progs/compute_live_registers.c 
b/tools/testing/selftests/bpf/progs/compute_live_registers.c
index 6884ab99a421..01d73ad76faf 100644
--- a/tools/testing/selftests/bpf/progs/compute_live_registers.c
+++ b/tools/testing/selftests/bpf/progs/compute_live_registers.c
@@ -249,11 +249,13 @@ __naked void if3_jset_bug(void)
        asm volatile (
                "r0 = 1;"
                "r2 = 2;"
-               "if r1 & 0x7 goto +1;"
+               ".8byte %[jset];" /* same as 'if r1 & 0x7 goto +1;' */
                "exit;"
                "r0 = r2;"
                "exit;"
-               ::: __clobber_all);
+               :
+               : __imm_insn(jset, BPF_JMP_IMM(BPF_JSET, BPF_REG_1, 0x7, 1))
+               : __clobber_all);
 }