Method rewriteCodeForLatency

src/instrument.cpp:508–671

}

Result BytecodeRewriter::rewriteCodeForLatency(const u8* code, u16 code_length, u8 start_time_loc_index, u16* relocation_table, Latency latency) {
    // Method start is relocated
    u16 current_relocation = EXTRA_BYTECODES_ENTRY;

    u32 code_start = _dst_len;

    put8(JVM_OPC_invokestatic);
    put16(_nanoTime_cpool_idx);

    put8(JVM_OPC_lstore);
    put8(start_time_loc_index);

    // nop ensures that tableswitch/lookupswitch needs no realignment
    put16(JVM_OPC_nop);
    put8(JVM_OPC_nop);

    // Low 16 bytes: jump base index
    // High 16 bytes: jump offset index
    // This supports narrow and wide jumps, as well as tableswitch and lookupswitch
    std::vector<u32> jumps;
    // First scan: fill relocation_table and rewrite code.
    for (u16 i = 0; i < code_length; /* incremented with instructionBytes */) {
        u8 opcode = code[i];

        if (isFunctionExit(opcode)) {
            put8(JVM_OPC_lload);
            put8(start_time_loc_index);

            if (latency > 0) {
                put8(JVM_OPC_ldc2_w);
                put16(_latency_cpool_idx[latency]);
            } else {
                put8(JVM_OPC_nop);
                put8(JVM_OPC_nop);
                put8(JVM_OPC_nop);
            }

            put8(JVM_OPC_invokestatic);
            put16(latency == 0 ? _recordExit_latency0_cpool_idx : _recordExit_cpool_idx);
        } else if (isNarrowJump(opcode) || isWideJump(opcode)) {
            jumps.push_back((i + 1U) << 16 | i);
        } else if (opcode == JVM_OPC_tableswitch) {
            // 'default' lies after the padding
            u16 default_index = alignUp4(i);
            // 4 bytes: default
            jumps.push_back((u32) default_index << 16 | i);
            // 4 bytes: low
            int32_t l = get32(code + default_index + 4);
            // 4 bytes: high
            int32_t h = get32(code + default_index + 8);
            assert(h - l + 1 >= 0);
            assert(h - l + 1 <= 0xFFFF);
            u16 branches_base_index = default_index + 12;
            for (u16 c = 0; c < (u16) (h - l + 1); ++c) {
                jumps.push_back((branches_base_index + c * 4) << 16 | i);
            }
        } else if (opcode == JVM_OPC_lookupswitch) {
            // 'default' lies after the padding