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Wed, 02 Sep 2026 10:44:07 -0700 (PDT) Received: from mail.gmail.com ([2a04:ee41:4:b2de:1ac0:4dff:fe0f:3782]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48448ed3840sm8090720f8f.17.2026.09.02.10.44.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2026 10:44:07 -0700 (PDT) Date: Wed, 2 Sep 2026 17:54:42 +0000 From: Anton Protopopov To: Siddharth Chintamaneni Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Puranjay Mohan , rlmenge@gmail.com, hargar@linux.microsoft.com, apais@microsoft.com Subject: Re: [PATCH bpf-next v4 2/2] selftests/bpf: Test terminal gotox instructions Message-ID: References: <20260902171414.96165-1-sidchintamaneni@gmail.com> <20260902171414.96165-2-sidchintamaneni@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260902171414.96165-2-sidchintamaneni@gmail.com> On 26/09/02 05:14PM, Siddharth Chintamaneni wrote: > Add tests that place gotox at the end of the main program and a > subprogram, with each jump-table target preceding the gotox instruction. > This tests gotox as a valid non-fallthrough terminal instruction. > > Signed-off-by: Siddharth Chintamaneni > --- > .../selftests/bpf/progs/verifier_gotox.c | 48 +++++++++++++++++++ > 1 file changed, 48 insertions(+) > > diff --git a/tools/testing/selftests/bpf/progs/verifier_gotox.c b/tools/testing/selftests/bpf/progs/verifier_gotox.c > index 5b18c9a27717..0e27c2c79c57 100644 > --- a/tools/testing/selftests/bpf/progs/verifier_gotox.c > +++ b/tools/testing/selftests/bpf/progs/verifier_gotox.c > @@ -47,6 +47,54 @@ DEFINE_SIMPLE_JUMP_TABLE_PROG(reserved_field_src_reg, BPF_REG_1, 0, 0, __fa > DEFINE_SIMPLE_JUMP_TABLE_PROG(reserved_field_non_zero_off, BPF_REG_0, 1, 0, __failure __msg("BPF_JA|BPF_X uses reserved fields")) > DEFINE_SIMPLE_JUMP_TABLE_PROG(reserved_field_non_zero_imm, BPF_REG_0, 0, 1, __failure __msg("BPF_JA|BPF_X uses reserved fields")) > > +#define DEFINE_TERMINAL_GOTOX_PROG(NAME, BASE) \ > + __naked void NAME(void) \ > + { \ > + asm volatile (" \ > + .pushsection .jumptables,\"\",@progbits; \ > +jt0_%=: \ > + .quad ret0_%= - " BASE "; \ > + .size jt0_%=, 8; \ > + .global jt0_%=; \ > + .popsection; \ > + \ > + r0 = jt0_%= ll; \ > + r0 = *(u64 *)(r0 + 0); \ > + goto end_%=; \ > +ret0_%=: \ > + r0 = 0; \ > + exit; \ > +end_%=: \ > + .8byte %[gotox_r0]; \ > +" : \ > + : __imm_insn(gotox_r0, BPF_RAW_INSN(BPF_JMP | BPF_JA | BPF_X, \ > + BPF_REG_0, 0, 0, 0)) \ > + : __clobber_all); \ > + } > + > +SEC("socket") > +__success __retval(0) > +DEFINE_TERMINAL_GOTOX_PROG(jump_table_terminal_gotox, "socket") > + > +static __noinline __used > +DEFINE_TERMINAL_GOTOX_PROG(terminal_gotox_subprog1, ".text") > + > +static __noinline __used int terminal_gotox_subprog2(void) > +{ > + return 0; > +} TBH, I was thinking about DEFINE_TERMINAL_GOTOX_PROG(terminal_gotox_subprog1, ".text") DEFINE_TERMINAL_GOTOX_PROG(terminal_gotox_subprog2, ".text") such that one shouldn't think in which order subprogs are added. But your variant should work. Reviewed-by: Anton Protopopov > +SEC("socket") > +__success __retval(0) > +__naked void jump_table_terminal_gotox_subprog(void) > +{ > + asm volatile (" \ > + call terminal_gotox_subprog1; \ > + call terminal_gotox_subprog2; \ > + exit; \ > +" ::: __clobber_all); > +} > + > /* > * Gotox is forbidden when there is no jump table loaded > * which points to the sub-function where the gotox is used > -- > 2.43.0 >