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[v3,bpf-next,5/6] bpf: Add bpf_nop_mov() asm macro.

Message ID 20231226191148.48536-6-alexei.starovoitov@gmail.com (mailing list archive)
State Accepted
Commit 0bcc62aa9813f519db58df14ddf1d523fa971e62
Delegated to: BPF
Headers show
Series bpf: volatile compare | expand

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Commit Message

Alexei Starovoitov Dec. 26, 2023, 7:11 p.m. UTC 
From: Alexei Starovoitov <ast@kernel.org>

bpf_nop_mov(var) asm macro emits nop register move: rX = rX.
If 'var' is a scalar and not a fixed constant the verifier will assign ID to it.
If it's later spilled the stack slot will carry that ID as well.
Hence the range refining comparison "if rX < const" will update all copies
including spilled slot.
This macro is a temporary workaround until the verifier gets smarter.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/testing/selftests/bpf/bpf_experimental.h | 5 +++++
 1 file changed, 5 insertions(+)
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 4c5ba91fa55a..6ecee9866970 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -323,6 +323,11 @@  l_true:\
        })
 #endif
 
+#ifndef bpf_nop_mov
+#define bpf_nop_mov(var) \
+	asm volatile("%[reg]=%[reg]"::[reg]"r"((short)var))
+#endif
+
 /* Description
  *	Assert that a conditional expression is true.
  * Returns