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SoFixer Workflow and Function Call Sequence

Overview

SoFixer reconstructs ELF files that have been dumped from memory, fixing the corrupted structures and relocations to create working shared library (.so) files.

Main Execution Flow

  1. Program Entry (main.cpp:121-128)

main() → main_loop() → usage() [on failure]

  1. Command Line Processing (main.cpp:28-119)
  • getopt_long() - Parse command line arguments
  • Key parameters handled:
  • -s: Source dumped SO file
  • -o: Output fixed SO file
  • -m: Memory dump base address
  • -b: Original SO file (experimental)
  • -d: Debug mode
  1. ELF Loading Phase (main.cpp:87-99)

ObElfReader elf_reader; elf_reader.setSource() → elf_reader.setDumpSoBaseAddr() → elf_reader.setBaseSoName() [optional] → elf_reader.Load()

  1. ObElfReader.Load() (ObElfReader.cpp:51-84)

ReadElfHeader() → VerifyElfHeader() → ReadProgramHeader() → FixDumpSoPhdr() → [LoadDynamicSectionFromBaseSource()] [if needed] → ReserveAddressSpace() → LoadSegments() → FindPhdr() → [ApplyDynamicSection()] [if base SO used] → ApplyPhdrTable()

  1. ELF Rebuilding Phase (main.cpp:101-115)

ElfRebuilder elf_rebuilder(&elf_reader); elf_rebuilder.Rebuild() → [Write output file with rebuild data]

  1. ElfRebuilder.Rebuild() (ElfRebuilder.cpp:540-546)

RebuildPhdr() → ReadSoInfo() → RebuildShdr() → RebuildRelocs() → RebuildFin()

Detailed Function Analysis

ObElfReader Key Functions

  • FixDumpSoPhdr() (ObElfReader.cpp:12-49)
  • Fixes corrupted program headers from memory dumps
  • Adjusts segment sizes and offsets for dumped memory layout
  • LoadDynamicSectionFromBaseSource() (ObElfReader.cpp:108-140)
  • Loads dynamic section from original SO file when missing from dump
  • Extracts essential linking information

ElfRebuilder Key Functions

  • RebuildPhdr() (ElfRebuilder.cpp:24-39)
  • Fixes program header table offsets and sizes
  • Aligns file structure with memory layout
  • ReadSoInfo() (ElfRebuilder.cpp:548-705)
  • Parses dynamic section to extract symbols, relocations, and metadata
  • Populates soinfo structure with linking information
  • RebuildShdr() (ElfRebuilder.cpp:41-538)
  • Reconstructs section header table from scratch
  • Creates sections: .dynsym, .dynstr, .hash, .rel.dyn, .rel.plt, etc.
  • RebuildRelocs() (ElfRebuilder.cpp:781-811)
  • Fixes relocations by adjusting addresses relative to new base
  • Handles different relocation types (R_ARM_RELATIVE, etc.)
  • RebuildFin() (ElfRebuilder.cpp:708-735)
  • Assembles final ELF file with corrected headers and data
  • Outputs complete reconstructed SO file

Core Data Structures

  • soinfo (ElfRebuilder.h:20-88) - Mimics Android's soinfo structure
  • Elf_* typedefs (macros.h:14-36) - Handle 32/64-bit ELF formats
  • Program/Section headers - Standard ELF structures for metadata

Memory Management Pattern

The tool follows a three-stage memory management pattern:

  1. Load - Read dumped SO into memory with correct layout
  2. Parse - Extract symbols, relocations, and dynamic information
  3. Rebuild - Reconstruct valid ELF structure and write to disk