#define SEEN_MEM BIT(0) /* use mem[] for temporary storage */
#define SEEN_LITERAL BIT(1) /* code uses literals */
#define SEEN_FUNC BIT(2) /* calls C functions */
-#define SEEN_TAIL_CALL BIT(3) /* code uses tail calls */
#define SEEN_STACK (SEEN_FUNC | SEEN_MEM)
/*
* Save registers and create stack frame if necessary.
* See stack frame layout description in "bpf_jit.h"!
*/
-static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
+static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
+ u32 stack_depth)
{
/* No-op for hotpatching */
/* brcl 0,prologue_plt */
EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt);
jit->prologue_plt_ret = jit->prg;
- if (jit->seen & SEEN_TAIL_CALL) {
+ if (fp->aux->func_idx == 0) {
+ /* Initialize the tail call counter in the main program. */
/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */
_EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT);
} else {
/*
- * There are no tail calls. Insert nops in order to have
- * tail_call_start at a predictable offset.
+ * Skip the tail call counter initialization in subprograms.
+ * Insert nops in order to have tail_call_start at a
+ * predictable offset.
*/
bpf_skip(jit, 6);
}
REG_SET_SEEN(BPF_REG_5);
jit->seen |= SEEN_FUNC;
+ /*
+ * Copy the tail call counter to where the callee expects it.
+ *
+ * Note 1: The callee can increment the tail call counter, but
+ * we do not load it back, since the x86 JIT does not do this
+ * either.
+ *
+ * Note 2: We assume that the verifier does not let us call the
+ * main program, which clears the tail call counter on entry.
+ */
+ /* mvc STK_OFF_TCCNT(4,%r15),N(%r15) */
+ _EMIT6(0xd203f000 | STK_OFF_TCCNT,
+ 0xf000 | (STK_OFF_TCCNT + STK_OFF + stack_depth));
/* lgrl %w1,func */
EMIT6_PCREL_RILB(0xc4080000, REG_W1, _EMIT_CONST_U64(func));
/* %r1() */
* B1: pointer to ctx
* B2: pointer to bpf_array
* B3: index in bpf_array
- */
- jit->seen |= SEEN_TAIL_CALL;
-
- /*
+ *
* if (index >= array->map.max_entries)
* goto out;
*/
jit->prg = 0;
jit->excnt = 0;
- bpf_jit_prologue(jit, stack_depth);
+ bpf_jit_prologue(jit, fp, stack_depth);
if (bpf_set_addr(jit, 0) < 0)
return -1;
for (i = 0; i < fp->len; i += insn_count) {
return ret;
}
+
+bool bpf_jit_supports_subprog_tailcalls(void)
+{
+ return true;
+}