Class: Omnizip::Filters::BcjSparc

Inherits:
FilterBase
  • Object
show all
Defined in:
lib/omnizip/filters/bcj_sparc.rb

Overview

BCJ filter for SPARC executables.

This filter preprocesses SPARC machine code by converting relative addresses in CALL and BA (Branch Always) instructions to absolute addresses. SPARC uses 4-byte aligned instructions with big-endian encoding.

The filter improves compression by making branch targets position-independent.

Constant Summary collapse

INSTRUCTION_SIZE =

Size of SPARC instruction (4 bytes, big-endian)

4
FLAG =

Flag constant for address validation

1 << 22
OFFSET_MASK =

Mask for offset extraction

(FLAG << 3) - 1

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.metadata ⇒ Hash

Get metadata about this filter.

Returns:

  • (Hash) —

    Filter metadata



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# File 'lib/omnizip/filters/bcj_sparc.rb', line 133

def metadata
  {
    name: "BCJ-SPARC",
    description: "Branch converter for SPARC executables",
    architecture: "SPARC",
    alignment: 4,
    endian: "big",
  }
end

Instance Method Details

#decode(data, position = 0) ⇒ String

Decode (postprocess) SPARC executable data after decompression.

Reverses the encoding by converting absolute addresses back to relative addresses.

Parameters:

  • data (String) —

    Binary executable data

  • position (Integer) (defaults to: 0) —

    Current stream position

Returns:

  • (String) —

    Decoded binary data



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# File 'lib/omnizip/filters/bcj_sparc.rb', line 93

def decode(data, position = 0)
  return data.dup if data.bytesize < INSTRUCTION_SIZE

  result = data.b
  size = data.bytesize & ~(INSTRUCTION_SIZE - 1)
  i = 0
  pc = position - INSTRUCTION_SIZE

  while i < size
    instruction = extract_uint32_be(result, i)
    pc += INSTRUCTION_SIZE

    # Check for processed instruction pattern
    test_val = instruction + (5 << 29)
    test_val ^= 7 << 29
    test_val += FLAG

    if test_val.nobits?(0 - (FLAG << 1))
      # Extract absolute address
      absolute = (instruction << 2) & OFFSET_MASK

      # Convert to relative offset
      offset = absolute - pc

      # Encode back
      new_instruction = (offset & OFFSET_MASK) >> 2
      new_instruction |= 1 << 30
      write_uint32_be(result, i, new_instruction)
    end

    i += INSTRUCTION_SIZE
  end

  result
end

#encode(data, position = 0) ⇒ String

Encode (preprocess) SPARC executable data for compression.

Scans for CALL and BA instructions and converts relative addresses to absolute addresses.

Parameters:

  • data (String) —

    Binary executable data

  • position (Integer) (defaults to: 0) —

    Current stream position

Returns:

  • (String) —

    Encoded binary data



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# File 'lib/omnizip/filters/bcj_sparc.rb', line 48

def encode(data, position = 0)
  return data.dup if data.bytesize < INSTRUCTION_SIZE

  result = data.b
  size = data.bytesize & ~(INSTRUCTION_SIZE - 1)
  i = 0
  pc = position - INSTRUCTION_SIZE

  while i < size
    instruction = extract_uint32_be(result, i)
    pc += INSTRUCTION_SIZE

    # Check for CALL or BA instruction
    # The check is based on specific bit patterns in SPARC ISA
    test_val = instruction + (5 << 29)
    test_val ^= 7 << 29
    test_val += FLAG

    if test_val.nobits?(0 - (FLAG << 1))
      # Extract 22-bit offset (bits 0-21) or 30-bit for CALL
      offset = (instruction << 2) & OFFSET_MASK

      # Convert to absolute address
      absolute = offset + pc

      # Encode back
      new_instruction = (absolute & OFFSET_MASK) >> 2
      new_instruction |= 1 << 30
      write_uint32_be(result, i, new_instruction)
    end

    i += INSTRUCTION_SIZE
  end

  result
end