/*
 * Copyright (c) 2018, 2019, Oracle and/or its affiliates.
 *
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without modification, are
 * permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of
 * conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided
 * with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written
 * permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
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package com.oracle.truffle.llvm.parser.elf;

import com.oracle.truffle.llvm.parser.filereader.ObjectFileReader;
import com.oracle.truffle.llvm.runtime.except.LLVMParserException;
import org.graalvm.polyglot.io.ByteSequence;

public final class ElfReader extends ObjectFileReader {

    private static final int EI_NIDENT = 16;
    private static final int EI_CLASS = 4;
    private static final int EI_DATA = 5;
    private static final int ELFDATA2MSB = 2;
    private static final int ELFCLASS64 = 2;

    private final boolean is64Bit;

    private ElfReader(ByteSequence byteSequence, boolean littleEndian, boolean is64Bit) {
        super(byteSequence, littleEndian);
        this.is64Bit = is64Bit;
        setPosition(EI_NIDENT);
    }

    static ElfReader create(ByteSequence byteSequence) {
        checkIdent(byteSequence);
        return new ElfReader(byteSequence, !isBigEndian(byteSequence), is64Bit(byteSequence));
    }

    public boolean is64Bit() {
        return is64Bit;
    }

    public ByteSequence getStringTable(long offset, long size) {
        return byteSequence.subSequence((int) offset, (int) (offset + size));
    }

    private static boolean isBigEndian(ByteSequence ident) {
        return ident.byteAt(EI_DATA) == ELFDATA2MSB;
    }

    private static boolean is64Bit(ByteSequence ident) {
        return ident.byteAt(EI_CLASS) == ELFCLASS64;
    }

    private static void checkIdent(ByteSequence ident) {
        checkIndentByte(ident, 0, 0x7f);
        checkIndentByte(ident, 1, 'E');
        checkIndentByte(ident, 2, 'L');
        checkIndentByte(ident, 3, 'F');
    }

    private static void checkIndentByte(ByteSequence ident, int ind, int val) {
        if (ident.byteAt(ind) != val) {
            throw new LLVMParserException("Invalid ELF file!");
        }
    }
}