@@ -12257,6 +12257,20 @@ 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(0),
+ 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 = {
@@ -12279,6 +12293,29 @@ static struct tail_call_test tail_call_tests[] = {
},
};
+/*
+ * 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(test_bpf_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);
+}
+
static void __init destroy_tail_call_tests(struct bpf_array *progs)
{
int i;
@@ -12332,16 +12369,17 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
for (i = 0; i < len; i++) {
struct bpf_insn *insn = &fp->insnsi[i];
- if (insn->imm != TAIL_CALL_MARKER)
- continue;
-
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)
@@ -12349,6 +12387,13 @@ 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;
+ *insn = BPF_EMIT_CALL(test_bpf_func);
+ break;
}
}
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@anyfinetworks.com> --- lib/test_bpf.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 48 insertions(+), 3 deletions(-)