This patch adds a tail call limit test where the program also emits
a BPF_CALL to an external function prior to the tail call. Mainly
testing that JITed programs preserve its internal register state, for
example tail call count, across such external calls.
Signed-off-by: Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx>
---
lib/test_bpf.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 80 insertions(+), 3 deletions(-)
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 7475abfd2186..152193b4080f 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12202,6 +12202,30 @@ struct tail_call_test {
offset, TAIL_CALL_MARKER), \
BPF_JMP_IMM(BPF_TAIL_CALL, 0, 0, 0)
+/*
+ * A test function to be called from a BPF program, clobbering a lot of
+ * CPU registers in the process. A JITed BPF program calling this function
+ * must save and restore any caller-saved registers it uses for internal
+ * state, for example the current tail call count.
+ */
+BPF_CALL_1(bpf_test_func, u64, arg)
+{
+ char buf[64];
+ long a = 0;
+ long b = 1;
+ long c = 2;
+ long d = 3;
+ long e = 4;
+ long f = 5;
+ long g = 6;
+ long h = 7;
+
+ return snprintf(buf, sizeof(buf),
+ "%ld %lu %lx %ld %lu %lx %ld %lu %x",
+ a, b, c, d, e, f, g, h, (int)arg);
+}
+#define BPF_FUNC_test_func __BPF_FUNC_MAX_ID
+
/*
* Tail call tests. Each test case may call any other test in the table,
* including itself, specified as a relative index offset from the calling
@@ -12259,6 +12283,25 @@ static struct tail_call_test tail_call_tests[] = {
},
.result = MAX_TAIL_CALL_CNT + 1,
},
+ {
+ "Tail call count preserved across function calls",
+ .insns = {
+ BPF_ALU64_IMM(BPF_ADD, R1, 1),
+ BPF_STX_MEM(BPF_DW, R10, R1, -8),
+ BPF_CALL_REL(BPF_FUNC_get_numa_node_id),
+ BPF_CALL_REL(BPF_FUNC_ktime_get_ns),
+ BPF_CALL_REL(BPF_FUNC_ktime_get_boot_ns),
+ BPF_CALL_REL(BPF_FUNC_ktime_get_coarse_ns),
+ BPF_CALL_REL(BPF_FUNC_jiffies64),
+ BPF_CALL_REL(BPF_FUNC_test_func),
+ BPF_LDX_MEM(BPF_DW, R1, R10, -8),
+ BPF_ALU32_REG(BPF_MOV, R0, R1),
+ TAIL_CALL(0),
+ BPF_EXIT_INSN(),
+ },
+ .stack_depth = 8,
+ .result = MAX_TAIL_CALL_CNT + 1,
+ },
{
"Tail call error path, NULL target",
.insns = {
@@ -12333,17 +12376,19 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
/* Relocate runtime tail call offsets and addresses */
for (i = 0; i < len; i++) {
struct bpf_insn *insn = &fp->insnsi[i];
-
- if (insn->imm != TAIL_CALL_MARKER)
- continue;
+ long addr = 0;
switch (insn->code) {
case BPF_LD | BPF_DW | BPF_IMM:
+ if (insn->imm != TAIL_CALL_MARKER)
+ break;
insn[0].imm = (u32)(long)progs;
insn[1].imm = ((u64)(long)progs) >> 32;
break;
case BPF_ALU | BPF_MOV | BPF_K:
+ if (insn->imm != TAIL_CALL_MARKER)
+ break;
if (insn->off == TAIL_CALL_NULL)
insn->imm = ntests;
else if (insn->off == TAIL_CALL_INVALID)
@@ -12351,6 +12396,38 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
else
insn->imm = which + insn->off;
insn->off = 0;
+ break;
+
+ case BPF_JMP | BPF_CALL:
+ if (insn->src_reg != BPF_PSEUDO_CALL)
+ break;
+ switch (insn->imm) {
+ case BPF_FUNC_get_numa_node_id:
+ addr = (long)&numa_node_id;
+ break;
+ case BPF_FUNC_ktime_get_ns:
+ addr = (long)&ktime_get_ns;
+ break;
+ case BPF_FUNC_ktime_get_boot_ns:
+ addr = (long)&ktime_get_boot_fast_ns;
+ break;
+ case BPF_FUNC_ktime_get_coarse_ns:
+ addr = (long)&ktime_get_coarse_ns;
+ break;
+ case BPF_FUNC_jiffies64:
+ addr = (long)&get_jiffies_64;
+ break;
+ case BPF_FUNC_test_func:
+ addr = (long)&bpf_test_func;
+ break;
+ default:
+ err = -EFAULT;
+ goto out_err;
+ }
+ *insn = BPF_EMIT_CALL(BPF_CAST_CALL(addr));
+ if ((long)__bpf_call_base + insn->imm != addr)
+ *insn = BPF_JMP_A(0); /* Skip: NOP */
+ break;
}
}
--
2.30.2
