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Changes to simplify length calculation

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This commit is contained in:
jmlagor
2021-02-10 16:41:23 +00:00
parent ec19b5cdc3
commit 317a8a7f68
1 changed files with 12 additions and 28 deletions
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Ghidra/Features/Base/src/main/java/ghidra/app/util/bin/format/pe/cli/blobs/CliBlobCustomAttrib.java
+12 -28
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@@ -4,9 +4,9 @@
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*
* http://www.apache.org/licenses/LICENSE-2.0
*
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -46,20 +46,16 @@ public class CliBlobCustomAttrib extends CliBlob {
private static final byte CLIBLOBCUSTOMATTRIB_TYPE_FIELD = 0x53;
private static final byte CLIBLOBCUSTOMATTRIB_TYPE_PROPERTY = 0x54;
// SerString processing constants to validate and convert the
// length of the string
private static final int CLIBLOBCUSTOMATTRIB_STRING_BOUNDARY_64 = 0x40;
private static final int CLIBLOBCUSTOMATTRIB_STRING_BOUNDARY_128 = 0x80;
private static final int CLIBLOBCUSTOMATTRIB_STRING_BOUNDARY_192 = 0xC0;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_ONE = 0x01;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_TWO = 0x02;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_TWO_BITMASK = 0x7F;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_FOUR = 0x03;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_FOUR_BITMASK = 0x3F;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_BITMASK = 0x3F;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_SHIFT = 0x06;
private static final int CLIBLOBCUSTOMATTRIB_STRING_SIZE_BITMASK = 0x03;
private static final int CLIBLOBCUSTOMATTRIB_STRING_INDICATOR_SHIFT = 0x06;
private static final int CLIBLOBCUSTOMATTRIB_STRING_INDICATOR_BITMASK = 0x03;
// UTF-8 boundaries that help detect the end of a string where
// lengths aren't specified in FixedArg
@@ -308,38 +304,26 @@ public class CliBlobCustomAttrib extends CliBlob {
byte firstByte = reader.readNextByte();
// Shift the highest two bits to the bottom and mask off to detect the
// size of the field holding the size of the string (1, 2, or 4 bytes)
byte stringSizeIndicator = (byte) (firstByte >> CLIBLOBCUSTOMATTRIB_STRING_SIZE_SHIFT &
CLIBLOBCUSTOMATTRIB_STRING_SIZE_BITMASK);
// size of the field holding the size of the string (1, 2, or 4 bytes),
// then cut the indicator bits off the first byte of the length.
byte stringSizeIndicator = (byte) (firstByte >> CLIBLOBCUSTOMATTRIB_STRING_INDICATOR_SHIFT &
CLIBLOBCUSTOMATTRIB_STRING_INDICATOR_BITMASK);
firstByte = (byte) (firstByte & CLIBLOBCUSTOMATTRIB_STRING_SIZE_BITMASK);
if (stringSizeIndicator <= CLIBLOBCUSTOMATTRIB_STRING_SIZE_ONE) {
// A size less than 128 indicates this is the only size byte
length = firstByte;
}
else if (stringSizeIndicator == CLIBLOBCUSTOMATTRIB_STRING_SIZE_TWO) {
// A value in the first byte in range [128 - 191] indicates the size
// is stored as a Word and the value in the highest bit must be unset
lengthBytes = new byte[] { firstByte, reader.readNextByte() };
// Unset what will become the highest bit if it's set
lengthBytes[1] = (byte) (lengthBytes[1] & CLIBLOBCUSTOMATTRIB_STRING_SIZE_TWO_BITMASK);
// Convert from big-endian
buf = ByteBuffer.wrap(lengthBytes);
buf.order(ByteOrder.BIG_ENDIAN);
length = buf.getShort();
}
else if (stringSizeIndicator == CLIBLOBCUSTOMATTRIB_STRING_SIZE_FOUR) {
// A value in the first byte > 128 indicates the size is stored as
// a DWord and the first two bits must be unset
lengthBytes = new byte[Integer.BYTES];
lengthBytes[0] = firstByte;
lengthBytes[1] = reader.readNextByte();
lengthBytes[2] = reader.readNextByte();
lengthBytes[3] = reader.readNextByte();
// Unset what will become the highest two bits if they're set
lengthBytes[3] = (byte) (lengthBytes[3] & CLIBLOBCUSTOMATTRIB_STRING_SIZE_FOUR_BITMASK);
lengthBytes = new byte[] { firstByte, reader.readNextByte(), reader.readNextByte(),
reader.readNextByte() };
// Convert from big-endian
buf = ByteBuffer.wrap(lengthBytes);