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| author | Johan Almbladh <johan.almbladh@anyfinetworks.com> | 2021-08-09 11:18:25 +0200 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-08-10 11:33:22 +0200 |
| commit | 66e5eb8474554bc021e8a221c336bdaef13f7a69 (patch) | |
| tree | 11ae3f1b6a610b75377e923cbfb6a0f5826f4352 /lib/test_bpf.c | |
| parent | e5009b4636cb593c06243197fd0742ed2e6ac510 (diff) | |
| download | lwn-66e5eb8474554bc021e8a221c336bdaef13f7a69.tar.gz lwn-66e5eb8474554bc021e8a221c336bdaef13f7a69.zip | |
bpf, tests: Add branch conversion JIT test
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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210809091829.810076-11-johan.almbladh@anyfinetworks.com
Diffstat (limited to 'lib/test_bpf.c')
| -rw-r--r-- | lib/test_bpf.c | 43 |
1 files changed, 43 insertions, 0 deletions
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, ...", { }, |