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-rw-r--r--src/common/dwarf/bytereader.h165
1 files changed, 122 insertions, 43 deletions
diff --git a/src/common/dwarf/bytereader.h b/src/common/dwarf/bytereader.h
index ead61f0e..bda450d1 100644
--- a/src/common/dwarf/bytereader.h
+++ b/src/common/dwarf/bytereader.h
@@ -43,75 +43,154 @@ enum Endianness {
ENDIANNESS_LITTLE
};
-// Class that knows how to read both big endian and little endian
-// numbers, for use in DWARF2/3 reader.
-// Takes an endianness argument.
-// To read addresses and offsets, SetAddressSize and SetOffsetSize
-// must be called first.
+// A ByteReader knows how to read single- and multi-byte values of
+// various endiannesses, sizes, and encodings, as used in DWARF
+// debugging information.
class ByteReader {
public:
- explicit ByteReader(enum Endianness endian);
+ // Construct a ByteReader capable of reading one-, two-, four-, and
+ // eight-byte values according to ENDIANNESS, absolute machine-sized
+ // addresses, DWARF-style "initial length" values, and signed and
+ // unsigned LEB128 numbers.
+ explicit ByteReader(enum Endianness endianness);
virtual ~ByteReader();
- // Set the address size to SIZE, which sets up the ReadAddress member
- // so that it works.
- void SetAddressSize(uint8 size);
-
- // Set the offset size to SIZE, which sets up the ReadOffset member
- // so that it works.
- void SetOffsetSize(uint8 size);
-
- // Return the current offset size
- uint8 OffsetSize() const { return offset_size_; }
-
- // Return the current address size
- uint8 AddressSize() const { return address_size_; }
-
// Read a single byte from BUFFER and return it as an unsigned 8 bit
// number.
uint8 ReadOneByte(const char* buffer) const;
- // Read two bytes from BUFFER and return it as an unsigned 16 bit
- // number.
+ // Read two bytes from BUFFER and return them as an unsigned 16 bit
+ // number, using this ByteReader's endianness.
uint16 ReadTwoBytes(const char* buffer) const;
- // Read four bytes from BUFFER and return it as an unsigned 32 bit
- // number. This function returns a uint64 so that it is compatible
- // with ReadAddress and ReadOffset. The number it returns will
- // never be outside the range of an unsigned 32 bit integer.
+ // Read four bytes from BUFFER and return them as an unsigned 32 bit
+ // number, using this ByteReader's endianness. This function returns
+ // a uint64 so that it is compatible with ReadAddress and
+ // ReadOffset. The number it returns will never be outside the range
+ // of an unsigned 32 bit integer.
uint64 ReadFourBytes(const char* buffer) const;
- // Read eight bytes from BUFFER and return it as an unsigned 64 bit
- // number
+ // Read eight bytes from BUFFER and return them as an unsigned 64
+ // bit number, using this ByteReader's endianness.
uint64 ReadEightBytes(const char* buffer) const;
// Read an unsigned LEB128 (Little Endian Base 128) number from
- // BUFFER and return it as an unsigned 64 bit integer. LEN is set
- // to the length read. Everybody seems to reinvent LEB128 as a
- // variable size integer encoding, DWARF has had it for a long time.
+ // BUFFER and return it as an unsigned 64 bit integer. Set LEN to
+ // the number of bytes read.
+ //
+ // The unsigned LEB128 representation of an integer N is a variable
+ // number of bytes:
+ //
+ // - If N is between 0 and 0x7f, then its unsigned LEB128
+ // representation is a single byte whose value is N.
+ //
+ // - Otherwise, its unsigned LEB128 representation is (N & 0x7f) |
+ // 0x80, followed by the unsigned LEB128 representation of N /
+ // 128, rounded towards negative infinity.
+ //
+ // In other words, we break VALUE into groups of seven bits, put
+ // them in little-endian order, and then write them as eight-bit
+ // bytes with the high bit on all but the last.
uint64 ReadUnsignedLEB128(const char* buffer, size_t* len) const;
// Read a signed LEB128 number from BUFFER and return it as an
- // signed 64 bit integer. LEN is set to the length read.
+ // signed 64 bit integer. Set LEN to the number of bytes read.
+ //
+ // The signed LEB128 representation of an integer N is a variable
+ // number of bytes:
+ //
+ // - If N is between -0x40 and 0x3f, then its signed LEB128
+ // representation is a single byte whose value is N in two's
+ // complement.
+ //
+ // - Otherwise, its signed LEB128 representation is (N & 0x7f) |
+ // 0x80, followed by the signed LEB128 representation of N / 128,
+ // rounded towards negative infinity.
+ //
+ // In other words, we break VALUE into groups of seven bits, put
+ // them in little-endian order, and then write them as eight-bit
+ // bytes with the high bit on all but the last.
int64 ReadSignedLEB128(const char* buffer, size_t* len) const;
- // Read an offset from BUFFER and return it as an unsigned 64 bit
- // integer. DWARF2/3 define offsets as either 4 or 8 bytes,
- // generally depending on the amount of DWARF2/3 info present.
- uint64 ReadOffset(const char* buffer) const;
+ // Indicate that addresses on this architecture are SIZE bytes long. SIZE
+ // must be either 4 or 8. (DWARF allows addresses to be any number of
+ // bytes in length from 1 to 255, but we only support 32- and 64-bit
+ // addresses at the moment.) You must call this before using the
+ // ReadAddress member function.
+ //
+ // For data in a .debug_info section, or something that .debug_info
+ // refers to like line number or macro data, the compilation unit
+ // header's address_size field indicates the address size to use. Call
+ // frame information doesn't indicate its address size (a shortcoming of
+ // the spec); you must supply the appropriate size based on the
+ // architecture of the target machine.
+ void SetAddressSize(uint8 size);
+
+ // Return the current address size, in bytes. This is either 4,
+ // indicating 32-bit addresses, or 8, indicating 64-bit addresses.
+ uint8 AddressSize() const { return address_size_; }
// Read an address from BUFFER and return it as an unsigned 64 bit
- // integer. DWARF2/3 allow addresses to be any size from 0-255
- // bytes currently. Internally we support 4 and 8 byte addresses,
- // and will CHECK on anything else.
+ // integer, respecting this ByteReader's endianness and address size. You
+ // must call SetAddressSize before calling this function.
uint64 ReadAddress(const char* buffer) const;
- // Read a DWARF2/3 initial length field from START, and report the
- // length of the length field in LEN. Return the value of the length
- // field. Set this reader's offset size as indicated by the length
- // field's encoding.
+ // DWARF actually defines two slightly different formats: 32-bit DWARF
+ // and 64-bit DWARF. This is *not* related to the size of registers or
+ // addresses on the target machine; it refers only to the size of section
+ // offsets and data lengths appearing in the DWARF data. One only needs
+ // 64-bit DWARF when the debugging data itself is larger than 4GiB.
+ // 32-bit DWARF can handle x86_64 or PPC64 code just fine, unless the
+ // debugging data itself is very large.
+ //
+ // DWARF information identifies itself as 32-bit or 64-bit DWARF: each
+ // compilation unit and call frame information entry begins with an
+ // "initial length" field, which, in addition to giving the length of the
+ // data, also indicates the size of section offsets and lengths appearing
+ // in that data. The ReadInitialLength member function, below, reads an
+ // initial length and sets the ByteReader's offset size as a side effect.
+ // Thus, in the normal process of reading DWARF data, the appropriate
+ // offset size is set automatically. So, you should only need to call
+ // SetOffsetSize if you are using the same ByteReader to jump from the
+ // midst of one block of DWARF data into another.
+
+ // Read a DWARF "initial length" field from START, and return it as
+ // an unsigned 64 bit integer, respecting this ByteReader's
+ // endianness. Set *LEN to the length of the initial length in
+ // bytes, either four or twelve. As a side effect, set this
+ // ByteReader's offset size to either 4 (if we see a 32-bit DWARF
+ // initial length) or 8 (if we see a 64-bit DWARF initial length).
+ //
+ // A DWARF initial length is either:
+ //
+ // - a byte count stored as an unsigned 32-bit value less than
+ // 0xffffff00, indicating that the data whose length is being
+ // measured uses the 32-bit DWARF format, or
+ //
+ // - The 32-bit value 0xffffffff, followed by a 64-bit byte count,
+ // indicating that the data whose length is being measured uses
+ // the 64-bit DWARF format.
uint64 ReadInitialLength(const char* start, size_t* len);
+ // Read an offset from BUFFER and return it as an unsigned 64 bit
+ // integer, respecting the ByteReader's endianness. In 32-bit DWARF, the
+ // offset is 4 bytes long; in 64-bit DWARF, the offset is eight bytes
+ // long. You must call ReadInitialLength or SetOffsetSize before calling
+ // this function; see the comments above for details.
+ uint64 ReadOffset(const char* buffer) const;
+
+ // Return the current offset size, in bytes.
+ // A return value of 4 indicates that we are reading 32-bit DWARF.
+ // A return value of 8 indicates that we are reading 64-bit DWARF.
+ uint8 OffsetSize() const { return offset_size_; }
+
+ // Indicate that section offsets and lengths are SIZE bytes long. SIZE
+ // must be either 4 (meaning 32-bit DWARF) or 8 (meaning 64-bit DWARF).
+ // Usually, you should not call this function yourself; instead, let a
+ // call to ReadInitialLength establish the data's offset size
+ // automatically.
+ void SetOffsetSize(uint8 size);
+
private:
// Function pointer type for our address and offset readers.