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

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Message-Id: <20250827082452.1381181-1-yangfeng59949@163.com>
Date: Wed, 27 Aug 2025 16:24:52 +0800
From: Feng Yang <yangfeng59949@....com>
To: eddyz87@...il.com
Cc: andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	haoluo@...gle.com,
	john.fastabend@...il.com,
	jolsa@...nel.org,
	kpsingh@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	llvm@...ts.linux.dev,
	martin.lau@...ux.dev,
	sdf@...ichev.me,
	song@...nel.org,
	yangfeng59949@....com,
	yonghong.song@...ux.dev
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix the invalid operand for instruction issue

On Tue, 26 Aug 2025 21:48:43 -0700, Eduard Zingerman <eddyz87@...il.com> wrote:

> On Wed, 2025-08-27 at 11:15 +0800, Feng Yang wrote:
> > From: Feng Yang <yangfeng@...inos.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 <yangfeng@...inos.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);
 }