Re: [PATCH 08/14] bpf/tests: Add tests for ALU operations implemented with function calls
From: Yonghong Song <hidden>
Date: 2021-07-28 23:52:30
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netdev
On 7/28/21 10:04 AM, Johan Almbladh wrote:
quoted hunk ↗ jump to hunk
32-bit JITs may implement complex ALU64 instructions using function calls. The new tests check aspects related to this, such as register clobbering and register argument re-ordering. Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com> --- lib/test_bpf.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+)diff --git a/lib/test_bpf.c b/lib/test_bpf.c index eb61088a674f..1115e39630ce 100644 --- a/lib/test_bpf.c +++ b/lib/test_bpf.c@@ -1916,6 +1916,144 @@ static struct bpf_test tests[] = { { }, { { 0, -1 } } }, + { + /* + * Register (non-)clobbering test, in the case where a 32-bit + * JIT implements complex ALU64 operations via function calls. + */ + "INT: Register clobbering, R1 updated", + .u.insns_int = { + BPF_ALU32_IMM(BPF_MOV, R0, 0), + BPF_ALU32_IMM(BPF_MOV, R1, 123456789), + BPF_ALU32_IMM(BPF_MOV, R2, 2), + BPF_ALU32_IMM(BPF_MOV, R3, 3), + BPF_ALU32_IMM(BPF_MOV, R4, 4), + BPF_ALU32_IMM(BPF_MOV, R5, 5), + BPF_ALU32_IMM(BPF_MOV, R6, 6), + BPF_ALU32_IMM(BPF_MOV, R7, 7), + BPF_ALU32_IMM(BPF_MOV, R8, 8), + BPF_ALU32_IMM(BPF_MOV, R9, 9), + BPF_ALU64_IMM(BPF_DIV, R1, 123456789), + BPF_JMP_IMM(BPF_JNE, R0, 0, 10), + BPF_JMP_IMM(BPF_JNE, R1, 1, 9), + BPF_JMP_IMM(BPF_JNE, R2, 2, 8), + BPF_JMP_IMM(BPF_JNE, R3, 3, 7), + BPF_JMP_IMM(BPF_JNE, R4, 4, 6), + BPF_JMP_IMM(BPF_JNE, R5, 5, 5), + BPF_JMP_IMM(BPF_JNE, R6, 6, 4), + BPF_JMP_IMM(BPF_JNE, R7, 7, 3), + BPF_JMP_IMM(BPF_JNE, R8, 8, 2), + BPF_JMP_IMM(BPF_JNE, R9, 9, 1), + BPF_ALU32_IMM(BPF_MOV, R0, 1), + BPF_EXIT_INSN(), + }, + INTERNAL, + { }, + { { 0, 1 } } + }, + { + "INT: Register clobbering, R2 updated", + .u.insns_int = { + BPF_ALU32_IMM(BPF_MOV, R0, 0), + BPF_ALU32_IMM(BPF_MOV, R1, 1), + BPF_ALU32_IMM(BPF_MOV, R2, 2 * 123456789), + BPF_ALU32_IMM(BPF_MOV, R3, 3), + BPF_ALU32_IMM(BPF_MOV, R4, 4), + BPF_ALU32_IMM(BPF_MOV, R5, 5), + BPF_ALU32_IMM(BPF_MOV, R6, 6), + BPF_ALU32_IMM(BPF_MOV, R7, 7), + BPF_ALU32_IMM(BPF_MOV, R8, 8), + BPF_ALU32_IMM(BPF_MOV, R9, 9), + BPF_ALU64_IMM(BPF_DIV, R2, 123456789), + BPF_JMP_IMM(BPF_JNE, R0, 0, 10), + BPF_JMP_IMM(BPF_JNE, R1, 1, 9), + BPF_JMP_IMM(BPF_JNE, R2, 2, 8), + BPF_JMP_IMM(BPF_JNE, R3, 3, 7), + BPF_JMP_IMM(BPF_JNE, R4, 4, 6), + BPF_JMP_IMM(BPF_JNE, R5, 5, 5), + BPF_JMP_IMM(BPF_JNE, R6, 6, 4), + BPF_JMP_IMM(BPF_JNE, R7, 7, 3), + BPF_JMP_IMM(BPF_JNE, R8, 8, 2), + BPF_JMP_IMM(BPF_JNE, R9, 9, 1), + BPF_ALU32_IMM(BPF_MOV, R0, 1), + BPF_EXIT_INSN(), + }, + INTERNAL, + { }, + { { 0, 1 } } + },
It looks like the above two tests, "R1 updated" and "R2 updated" should be very similar and the only difference is one immediate is 123456789 and another is 2 * 123456789. But for generated code, they all just have the final immediate. Could you explain what the difference in terms of jit for the above two tests?
+ {
+ /*
+ * Test 32-bit JITs that implement complex ALU64 operations as
+ * function calls R0 = f(R1, R2), and must re-arrange operands.
+ */
+#define NUMER 0xfedcba9876543210ULL
+#define DENOM 0x0123456789abcdefULL
+ "ALU64_DIV X: Operand register permutations",
+ .u.insns_int = {
+ /* R0 / R2 */
+ BPF_LD_IMM64(R0, NUMER),
+ BPF_LD_IMM64(R2, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R0, R2),
+ BPF_JMP_IMM(BPF_JEQ, R0, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* R1 / R0 */
+ BPF_LD_IMM64(R1, NUMER),
+ BPF_LD_IMM64(R0, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R1, R0),
+ BPF_JMP_IMM(BPF_JEQ, R1, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* R0 / R1 */
+ BPF_LD_IMM64(R0, NUMER),
+ BPF_LD_IMM64(R1, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R0, R1),
+ BPF_JMP_IMM(BPF_JEQ, R0, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* R2 / R0 */
+ BPF_LD_IMM64(R2, NUMER),
+ BPF_LD_IMM64(R0, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R2, R0),
+ BPF_JMP_IMM(BPF_JEQ, R2, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* R2 / R1 */
+ BPF_LD_IMM64(R2, NUMER),
+ BPF_LD_IMM64(R1, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R2, R1),
+ BPF_JMP_IMM(BPF_JEQ, R2, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* R1 / R2 */
+ BPF_LD_IMM64(R1, NUMER),
+ BPF_LD_IMM64(R2, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R1, R2),
+ BPF_JMP_IMM(BPF_JEQ, R1, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ BPF_LD_IMM64(R0, 1),Do we need this BPF_LD_IMM64(R0, 1)? First, if we have it, and next "BPF_ALU64_REG(BPF_DIV, R1, R1)" generates incorrect value and exit and then you will get exit value 1, which will signal the test success. Second, if you don't have this R0 = 1, R0 will be DENOM and you will be fine.
+ /* R1 / R1 */
+ BPF_LD_IMM64(R1, NUMER),
+ BPF_ALU64_REG(BPF_DIV, R1, R1),
+ BPF_JMP_IMM(BPF_JEQ, R1, 1, 1),
+ BPF_EXIT_INSN(),
+ /* R2 / R2 */
+ BPF_LD_IMM64(R2, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R2, R2),
+ BPF_JMP_IMM(BPF_JEQ, R2, 1, 1),
+ BPF_EXIT_INSN(),
+ /* R3 / R4 */
+ BPF_LD_IMM64(R3, NUMER),
+ BPF_LD_IMM64(R4, DENOM),
+ BPF_ALU64_REG(BPF_DIV, R3, R4),
+ BPF_JMP_IMM(BPF_JEQ, R3, NUMER / DENOM, 1),
+ BPF_EXIT_INSN(),
+ /* Successful return */
+ BPF_LD_IMM64(R0, 1),
+ BPF_EXIT_INSN(),
+ },
+ INTERNAL,
+ { },
+ { { 0, 1 } },
+#undef NUMER
+#undef DENOM
+ },
{
"check: missing ret",
.u.insns = {