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From: Johan Almbladh <johan.almbladh@anyfinetworks.com>
To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org
Cc: kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
	john.fastabend@gmail.com, kpsingh@kernel.org,
	Tony.Ambardar@gmail.com, netdev@vger.kernel.org,
	bpf@vger.kernel.org,
	Johan Almbladh <johan.almbladh@anyfinetworks.com>
Subject: [PATCH bpf-next v2 10/14] bpf/tests: Add branch conversion JIT test
Date: Mon,  9 Aug 2021 11:18:25 +0200	[thread overview]
Message-ID: <20210809091829.810076-11-johan.almbladh@anyfinetworks.com> (raw)
In-Reply-To: <20210809091829.810076-1-johan.almbladh@anyfinetworks.com>

Some JITs may need to convert a conditional jump instruction to
to short PC-relative branch and a long unconditional jump, if the
PC-relative offset exceeds offset field width in the CPU instruction.
This test triggers such branch conversion on the 32-bit MIPS JIT.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
---
 lib/test_bpf.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 402c199cc119..896d37f4f4b3 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -461,6 +461,41 @@ static int bpf_fill_stxdw(struct bpf_test *self)
 	return __bpf_fill_stxdw(self, BPF_DW);
 }
 
+static int bpf_fill_long_jmp(struct bpf_test *self)
+{
+	unsigned int len = BPF_MAXINSNS;
+	struct bpf_insn *insn;
+	int i;
+
+	insn = kmalloc_array(len, sizeof(*insn), GFP_KERNEL);
+	if (!insn)
+		return -ENOMEM;
+
+	insn[0] = BPF_ALU64_IMM(BPF_MOV, R0, 1);
+	insn[1] = BPF_JMP_IMM(BPF_JEQ, R0, 1, len - 2 - 1);
+
+	/*
+	 * Fill with a complex 64-bit operation that expands to a lot of
+	 * instructions on 32-bit JITs. The large jump offset can then
+	 * overflow the conditional branch field size, triggering a branch
+	 * conversion mechanism in some JITs.
+	 *
+	 * Note: BPF_MAXINSNS of ALU64 MUL is enough to trigger such branch
+	 * conversion on the 32-bit MIPS JIT. For other JITs, the instruction
+	 * count and/or operation may need to be modified to trigger the
+	 * branch conversion.
+	 */
+	for (i = 2; i < len - 1; i++)
+		insn[i] = BPF_ALU64_IMM(BPF_MUL, R0, (i << 16) + i);
+
+	insn[len - 1] = BPF_EXIT_INSN();
+
+	self->u.ptr.insns = insn;
+	self->u.ptr.len = len;
+
+	return 0;
+}
+
 static struct bpf_test tests[] = {
 	{
 		"TAX",
@@ -6895,6 +6930,14 @@ static struct bpf_test tests[] = {
 		{ },
 		{ { 0, 1 } },
 	},
+	{	/* Mainly checking JIT here. */
+		"BPF_MAXINSNS: Very long conditional jump",
+		{ },
+		INTERNAL | FLAG_NO_DATA,
+		{ },
+		{ { 0, 1 } },
+		.fill_helper = bpf_fill_long_jmp,
+	},
 	{
 		"JMP_JA: Jump, gap, jump, ...",
 		{ },
-- 
2.25.1


  parent reply	other threads:[~2021-08-09  9:19 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09  9:18 [PATCH bpf-next v2 00/14] bpf/tests: Extend the eBPF test suite Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 01/14] bpf/tests: Add BPF_JMP32 test cases Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 02/14] bpf/tests: Add BPF_MOV tests for zero and sign extension Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 03/14] bpf/tests: Fix typos in test case descriptions Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 04/14] bpf/tests: Add more tests of ALU32 and ALU64 bitwise operations Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 05/14] bpf/tests: Add more ALU32 tests for BPF_LSH/RSH/ARSH Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 06/14] bpf/tests: Add more BPF_LSH/RSH/ARSH tests for ALU64 Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 07/14] bpf/tests: Add more ALU64 BPF_MUL tests Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 08/14] bpf/tests: Add tests for ALU operations implemented with function calls Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 09/14] bpf/tests: Add word-order tests for load/store of double words Johan Almbladh
2021-08-09  9:18 ` Johan Almbladh [this message]
2021-08-09  9:18 ` [PATCH bpf-next v2 11/14] bpf/tests: Add test for 32-bit context pointer argument passing Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 12/14] bpf/tests: Add tests for atomic operations Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 13/14] bpf/tests: Add tests for BPF_CMPXCHG Johan Almbladh
2021-08-09  9:18 ` [PATCH bpf-next v2 14/14] bpf/tests: Add tail call test suite Johan Almbladh
2021-08-10 11:00 ` [PATCH bpf-next v2 00/14] bpf/tests: Extend the eBPF " patchwork-bot+netdevbpf

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