From 3c2611bac08a834697be918ac357eaff2e47d5b3 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Tue, 14 Mar 2023 15:28:11 -0700 Subject: [PATCH] selftests/bpf: Fix trace_virtqueue_add_sgs test issue with LLVM 17. LLVM commit https://reviews.llvm.org/D143726 introduced hoistMinMax optimization that transformed (i < VIRTIO_MAX_SGS) && (i < out_sgs) into i < MIN(VIRTIO_MAX_SGS, out_sgs) and caused the verifier to stop recognizing such loop as bounded. Which resulted in the following test failure: libbpf: prog 'trace_virtqueue_add_sgs': BPF program load failed: Bad address libbpf: prog 'trace_virtqueue_add_sgs': -- BEGIN PROG LOAD LOG -- The sequence of 8193 jumps is too complex. verification time 789206 usec stack depth 56 processed 156446 insns (limit 1000000) max_states_per_insn 7 total_states 1746 peak_states 1701 mark_read 12 -- END PROG LOAD LOG -- libbpf: prog 'trace_virtqueue_add_sgs': failed to load: -14 libbpf: failed to load object 'loop6.bpf.o' Workaround the verifier limitation for now with inline asm that prevents this particular optimization. Signed-off-by: Alexei Starovoitov --- tools/testing/selftests/bpf/progs/loop6.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/loop6.c b/tools/testing/selftests/bpf/progs/loop6.c index 38de0331e6b4..e4ff97fbcce1 100644 --- a/tools/testing/selftests/bpf/progs/loop6.c +++ b/tools/testing/selftests/bpf/progs/loop6.c @@ -5,6 +5,7 @@ #include #include #include +#include "bpf_misc.h" char _license[] SEC("license") = "GPL"; @@ -76,6 +77,7 @@ int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs, return 0; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) { + __sink(out_sgs); for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX); sgp = __sg_next(sgp)) { bpf_probe_read_kernel(&len, sizeof(len), &sgp->length); @@ -85,6 +87,7 @@ int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs, } for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) { + __sink(in_sgs); for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX); sgp = __sg_next(sgp)) { bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);