s390/bpf: implement bpf_tail_call() helper
bpf_tail_call() arguments: - ctx......: Context pointer - jmp_table: One of BPF_MAP_TYPE_PROG_ARRAY maps used as the jump table - index....: Index in the jump table In this implementation s390x JIT does stack unwinding and jumps into the callee program prologue. Caller and callee use the same stack. With this patch a tail call generates the following code on s390x: if (index >= array->map.max_entries) goto out 000003ff8001c7e4: e31030100016 llgf %r1,16(%r3) 000003ff8001c7ea: ec41001fa065 clgrj %r4,%r1,10,3ff8001c828 if (tail_call_cnt++ > MAX_TAIL_CALL_CNT) goto out; 000003ff8001c7f0: a7080001 lhi %r0,1 000003ff8001c7f4: eb10f25000fa laal %r1,%r0,592(%r15) 000003ff8001c7fa: ec120017207f clij %r1,32,2,3ff8001c828 prog = array->prog[index]; if (prog == NULL) goto out; 000003ff8001c800: eb140003000d sllg %r1,%r4,3 000003ff8001c806: e31310800004 lg %r1,128(%r3,%r1) 000003ff8001c80...
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941742f4
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