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authorYonghong Song <yhs@fb.com>2022-04-19 07:09:00 +0200
committerAlexei Starovoitov <ast@kernel.org>2022-04-19 19:22:19 +0200
commit44df171a10f8969d1456e0a5af7fbac142d7fa18 (patch)
treedaab59e7a6f1dc1cc86cf6562adc8f585891b0c4 /tools/testing
parentselftests/bpf: Limit unroll_count for pyperf600 test (diff)
downloadlinux-44df171a10f8969d1456e0a5af7fbac142d7fa18.tar.xz
linux-44df171a10f8969d1456e0a5af7fbac142d7fa18.zip
selftests/bpf: Workaround a verifier issue for test exhandler
The llvm patch [1] enabled opaque pointer which caused selftest 'exhandler' failure. ... ; work = task->task_works; 7: (79) r1 = *(u64 *)(r6 +2120) ; R1_w=ptr_callback_head(off=0,imm=0) R6_w=ptr_task_struct(off=0,imm=0) ; func = work->func; 8: (79) r2 = *(u64 *)(r1 +8) ; R1_w=ptr_callback_head(off=0,imm=0) R2_w=scalar() ; if (!work && !func) 9: (4f) r1 |= r2 math between ptr_ pointer and register with unbounded min value is not allowed below is insn 10 and 11 10: (55) if r1 != 0 goto +5 11: (18) r1 = 0 ll ... In llvm, the code generation of 'r1 |= r2' happened in codegen selectiondag phase due to difference of opaque pointer vs. non-opaque pointer. Without [1], the related code looks like: r2 = *(u64 *)(r6 + 2120) r1 = *(u64 *)(r2 + 8) if r2 != 0 goto +6 <LBB0_4> if r1 != 0 goto +5 <LBB0_4> r1 = 0 ll ... I haven't found a good way in llvm to fix this issue. So let us workaround the problem first so bpf CI won't be blocked. [1] https://reviews.llvm.org/D123300 Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220419050900.3136024-1-yhs@fb.com
Diffstat (limited to 'tools/testing')
-rw-r--r--tools/testing/selftests/bpf/progs/exhandler_kern.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/tools/testing/selftests/bpf/progs/exhandler_kern.c b/tools/testing/selftests/bpf/progs/exhandler_kern.c
index f5ca142abf8f..dd9b30a0f0fc 100644
--- a/tools/testing/selftests/bpf/progs/exhandler_kern.c
+++ b/tools/testing/selftests/bpf/progs/exhandler_kern.c
@@ -7,6 +7,8 @@
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_core_read.h>
+#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var))
+
char _license[] SEC("license") = "GPL";
unsigned int exception_triggered;
@@ -37,7 +39,16 @@ int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags)
*/
work = task->task_works;
func = work->func;
- if (!work && !func)
- exception_triggered++;
+ /* Currently verifier will fail for `btf_ptr |= btf_ptr` * instruction.
+ * To workaround the issue, use barrier_var() and rewrite as below to
+ * prevent compiler from generating verifier-unfriendly code.
+ */
+ barrier_var(work);
+ if (work)
+ return 0;
+ barrier_var(func);
+ if (func)
+ return 0;
+ exception_triggered++;
return 0;
}