LogoLogo
IDA 8.4
IDA 8.4
  • Welcome to Hex-Rays docs
  • User Guide
    • User Interface
      • Menu Bar
        • File
          • Load file
          • Script File
          • Script command
          • Produce output files
          • Invoke OS Shell
          • Take database snapshot
          • Save database
          • Save database as...
          • Abort IDA
          • Exit IDA
        • Edit
          • Export data
          • Undo an action
          • Redo an action
          • Clear undo history
          • Disable undo
          • Convert to instruction
          • Convert to data
          • Convert to string literal
          • Convert to array
          • Undefine a byte
          • Give Name to the Location
          • Operand types
            • Offset
            • Number
            • Perform en masse operation
            • Convert operand to character
            • Convert operand to segment
            • Complex Offset Expression
            • Convert operand to symbolic constant (enum)
            • Convert operand to stack variable
            • Change operand sign
            • Bitwise negate operand
            • User-defined operand
            • Set operand type
          • Comments
          • Functions
          • Structures
            • Enums
          • Segments
          • Patch core
          • Other
            • Rename Any Address
          • Plugins
        • Jump
          • Center current line in window
          • Problems List
        • Search
          • REGULAR EXPRESSION SYNTAX SUMMARY
        • View
          • Open subviews
          • Graphs
          • Message Window
          • Arrows window
          • Database snapshot manager
          • Highlighting identifiers
          • Browser options
          • Lumina options
          • Assembler level and C level types
          • C++ type details
          • Bookmarks window
          • Calculator
          • View segment registers
          • View Internal Flags
          • Hide
          • Unhide
          • Del hidden range
          • Hide all items
          • Unhide all items
          • Setup hidden items
        • Debugger
          • Debugger window
          • Process Control
            • Start process
            • Process options
            • Pause process
            • Terminate process
            • Step into
            • Step over
            • Run to cursor
            • Run until return
            • Attach to process
            • Detach from process
            • Set current ip
            • Show application screen
          • Breakpoints
          • Watches
          • Tracing
          • Source code view
            • Watch view (source level)
          • Process Memory
            • Take memory snapshot
            • Manual memory regions
            • Refresh memory
          • Thread list
          • Module list
          • Stack trace
          • Exceptions
          • Debugger options
          • Switch debugger
        • Lumina
        • Options
          • Low & High Suspicious Operand Limits
        • Windows
          • Rename a stack variable
          • Miscellanous Options
          • Environment variables
          • Reset Hidden Messages
          • Various dialog help messages
        • List of all menu options
      • Desktops
      • Command line
      • How To Use List Viewers in IDA
      • Licenses
        • Apache License for Ghidra
        • Apache License for LLVM
        • Common Public License Version 1.0
        • APPLE PUBLIC SOURCE LICENSE
        • PCRE2 LICENCE
        • GNU Lesser General Public License v2.1 for libiberty
      • Database conversion from idb to i64
    • Disassembler
      • Interactivity
      • Background Analysis
      • Graph view
        • Graphing tutorial
      • Proximity view
      • Navigation
        • Anchor
        • How to Enter a Segment Value
        • How to Enter a Number
        • How to Enter an Identifier
        • How to enter text
        • How to Enter an Address
      • Disassembly Gallery
        • Philips 51XA-G3
        • 6502 and 65C02 Disassembler
        • 6301, 6303, 6800, 6801 and 6803 Disassembler
        • 68040, Amiga
        • 6805 Disassembler
        • 6808 Disassembler
        • 6809 OS9 Flex Disassembler
        • 6809 Disassembler
        • 6811 Disassembler
        • 68HC12 Disassembler
        • 68HC16 Disassembler
        • 68k Amiga Disassembler
        • 68k Mac OS
        • 68k Palm Pilot
        • Unix COFF
        • NEC 78k0 and 78k0s Processor
        • 80196 Processor
        • 8051 Disassembler
        • Analog Devices 218x.
        • Alpha Processor – NT COFF
        • Alpha Processor – Unix ELF
        • Android ARM Executables (.elf)
        • ARC Processor
        • ARM Processor EPOC App
        • ARM Processor EPOC PE File
        • ARM Processor EPOC ROMFile
        • EPOC SIS File Handler
        • ARM Processor iOS (iPhone): Unlock
        • ARM Processor iOS (iPhone): Objective-C metadata
        • ARM Processor iOS (iPhone): Objective-C Instance variables
        • ARM Processor iOS (iPhone): Parameter Identification & Tracking (PIT)
        • ARM Processor iOS (iPhone): Start
        • ARM Processor iOS (iPhone): Switch statements
        • ARM Processor iOS (iPhone): C++ signatures
        • ARM Processor iOS (iPhone): Write
        • ARM Processor: Linux ELF
        • ARM Processor: AOF SDK
        • ARM Processor: Windows CE COFF Format
        • ARM Processor: Windows CE PE Format
        • ATMEL AVR Disassembler
        • C166 Processor
        • C166 Processor with ELF file
        • Rockwell C39
        • Microsoft .NET CLI Disassembler. VisualBasic library
        • CR16
        • Android Dalvik Executables (.dex)
        • Microsoft .NET CLI Disassembler
        • DSP56K
        • Fujitsu FR (.elf)
        • Gameboy
        • H8 300: COFF FILE Format
        • H8 300s: COFF FILE Format
        • H8 500
        • HPPA Risc Processor: HP-UX SOM
        • i51
        • i860
        • Intel i960
        • Intel IA-64 (Itanium)
        • Java Bytecode
        • Angstrem KR 1878
        • Renesas/Hitachi M16C
        • Renesas/Hitachi M32R
        • M740
        • M7700
        • M7900
        • MIPS Processor: Nintendo N64
        • MIPS R5900 Processor : Sony bin
        • MIPS Processor: Sony ELF
        • MIPS Processor: Sony PSX
        • MIPS Processor: Sony PSX
        • MIPS Processor: Unix COFF File Format
        • MIPS Processor: Unix ELF File Format
        • MIPS Processor: Windows CE PE File Format
        • MIPS Processor: Windows CE PE2 File Format
        • Panasonic MN102
        • Atmel OAK DSP
        • 80×86 Architecture: DOS Extender
        • 80×86 Architecture: Watcom Runtime
        • 80×86 Architecture: Geos APP
        • 80×86 Architecture: Geos DRV
        • 80×86 Architecture: Geos LIB
        • 80×86 Architecture: GNU COFF Format
        • 80×86 Architecture: OS/2 Linear Executable Format
        • 80×86 Architecture: Netware NLM
        • 80×86 Architecture: QNX Executable
        • 80×86 Architecture: Watcom Runtime
        • 80×86 Architecture: Windows OMF
        • 80×86 Architecture: Windows Portable Executable Format
        • 80×86 Architecture: Windows Virtual Device Driver
        • 80×86 Architecture: Windows 16 bits DLL
        • X-Box Disassembler
        • PDP 11: SAV File
        • PIC
        • PIC 12xx
        • Power PC AIF ECOFF file Format
        • Power PC Linux ELF
        • Mac OS PEF File
        • Mac OS X File
        • Windows NT PE File
        • Hitachi SH-1 Processor
        • Hitachi SH-3 Processor: Windows CE COFF format
        • Hitachi SH-3 Processor: Windows CE PE format
        • Hitachi SH-4 Processor: ELF File Format
        • Hitachi SH-4 Processor: Windows CE PE File Format
        • Super Nintendo Entertainement System (SNES)
        • SPARC Solaris COFF
        • SPARC Solaris ELF
        • SPARC Sun ELF
        • SPARC Sun ELF SO
        • ST 20C4
        • ST 7
        • ST 9
        • Toshiba TLCS 900
        • TMS 320c2 COFF
        • TMS 320c5
        • TMS 320c54
        • TMS 320c6 COFF File Format
        • TRICORE
        • SunPlus unSP
        • NEC V850
        • Z180 COFF File Format
        • Z380 COFF File Format
        • Z8
        • Z80
      • Supported processors
      • Supported file formats
        • Windmp file loader
      • Bitfields
        • Bit Fields tutorial
      • Structures tutorial
      • Union tutorial
      • Variable length structures tutorial
      • Data types, operands and constructs
      • Packed executables
    • Decompiler
      • Prerequisites
      • Quick primer
      • Exception handler
      • Introduction to Decompilation vs. Disassembly
        • Comparisons of ARM disassembly and decompilation
        • Comparisons of PowerPC disassembly and decompilation
        • Comparisons of MIPS disassembly and decompilation
        • Hex-Rays v7.4 vs. v7.3 Decompiler Comparison Page
        • Hex-Rays v7.3 vs. v7.2 Decompiler Comparison Page
        • Hex-Rays v7.2 vs. v7.1 Decompiler Comparison Page
      • Interactive operation
        • Rename
        • Set type
        • Set number representation
        • Edit indented comment
        • Edit block comment
        • Hide/unhide C statements
        • Split/unsplit expression
        • Force call type
        • Set call type
        • Add/del variadic arguments
        • Del function argument
        • Add/delete function return type
        • Jump to cross reference
        • Jump to cross reference globally
        • Generate HTML file
        • Mark/unmark as decompiled
        • Copy to assembly
        • Show/hide casts
        • Reset pointer type
        • Convert to struct *
        • Create new struct type
        • Split variable
        • Select union field
        • Jump to paired paren
        • Collapse/uncollapse item
        • Map to another variable
      • Batch operation
      • Configuration
      • Third party plugins
      • Floating point support
      • Support for intrinsic functions
      • Overlapped variables
      • gooMBA
      • Failures and troubleshooting
      • FAQ
      • Limitations
      • Tips and tricks
    • Debugger
      • Instant debugger
      • Remote debugging
        • Remote iOS Debugger
        • Android debugger
        • Dalvik debugger
        • Remote GDB Debugger
          • Remote GDB Debugger options
          • Debugging with gdbserver
          • Debugging with VMWare
          • Debugging with OpenOCD
          • Debugging with QEMU
          • External programs and GDB Debugger
          • Debugging code snippets with QEMU
        • PIN debugger
          • Building the PIN tool
          • Connecting a remote PIN tool instance from IDA
          • PIN support for MacOSX
        • Replayer debugger
        • Bochs debugger
          • Bochs Disk Image operation mode
          • Bochs IDB operation mode
          • Bochs PE operation mode
          • Bochs debugger FAQ
      • Local debugging
        • WinDbg Debugger
        • Linux debugger
        • Intel/ARM macOS debugger
      • Debugger tutorials
        • Debugging Dalvik Programs
        • IDA Win32 Local Debugging
        • IDA Linux Local Debugging
        • IDA Win32 to Win32 Debugging
        • IDA Win32 to Win64 Debugging
        • Debugging Mac OSX Applications with IDA Pro
        • Debugging iOS Applications with IDA Pro
        • Debugging Linux Applications locally
        • Debugging Linux/Windows Applications with PIN Tracer module
        • Debugging Windows Applications with IDA Bochs Plugin
        • Debugging Windows Applications with IDA WinDbg Plugin
        • Using the Bochs debugger plugin in Linux
        • Debugging Windows Kernel with VMWare and IDA WinDbg Plugin
        • Debugging Linux Kernel under VMWare using IDA GDB debugger
        • Windows Debugger Hub
        • Linux Debugger
        • Debugging a Windows executable locally and remotely
        • Debugging the XNU Kernel with IDA Pro
        • Remote debugging with IDA Pro
        • IDA Scriptable Debugger: overview
          • IDA Scriptable Debugger: scriptability
        • Debugging code snippets with QEMU debugger (a la IDA Bochs debugger)
        • Trace Replayer and managing traces
        • Using IDA Pro's tracing features
        • Working with PIN
        • Appcall
    • Signatures
      • FLIRT
        • IDA F.L.I.R.T. Technology: In-Depth
        • Supported Compilers
          • Turbo Pascal
          • Delphi
      • Makesig
    • Type Libraries
      • IDAClang
      • TILIB
    • Configuration
      • Configuration files
      • Command line switches
      • Keyboard macros
    • Teams
      • IDA Teams Licenses
      • Diffing and Merging Databases with IDA Teams
      • Teams lc command reference manual
      • hv command reference manual
      • Hex-Rays Vault’s visual client user manual
    • Lumina
      • lc command reference manual
    • Plugins
      • Open Plugin Architecture
      • Plugin options
      • Plugins Shipped with IDA
        • Swift plugin
        • Golang plugin
        • Rust plugin
        • picture_search
        • Objective-C Analysis Plugin
        • DYLD Shared Cache Utils
      • Plugin Contest
      • How to write your own plugin?
    • Helper Tools
  • Developer Guide
    • C++ SDK
      • C++ SDK reference
      • Using the Decompiler SDK: Decompiler Plug-In
    • IDAPython
      • IDAPython API Reference
    • IDC
      • Core concepts
        • Expressions
        • Statements
        • Functions
        • Variables
        • Constants
        • Exceptions
        • Classes
        • Predefined symbols
        • loader_input_t class
        • Slices
      • IDC API Reference
        • Index of debugger related IDC functions
        • Alphabetical list of IDC functions
          • set_selector
          • enable_tracing
          • get_prev_fixup_ea
          • del_segm
          • get_bmask_cmt
          • end_type_updating
          • Find
          • toggle_bnot
          • patch_byte
          • get_module_info
          • set_member_name
          • create_float
          • del_struc_member
          • read_dbg_memory
          • get_enum_width
          • getn_thread_name
          • del_struc
          • filelength
          • set_manual_insn
          • is_value...() functions
          • get_ip_val
          • del_extra_cmt
          • create_insn
          • op_offset_high16
          • get_cmt
          • expand_struc
          • get_idb_path
          • set_frame_size
          • get_file_ext
          • has_value
          • readshort
          • sanitize_file_name
          • get_member_flag
          • create_struct
          • ARM specific
          • Disk Write Error
          • set_enum_member_cmt
          • rename
          • set_ida_state
          • get_member_size
          • msg
          • qbasename
          • get_enum_member_enum
          • auto_mark_range
          • plan_to_apply_idasgn
          • set_named_type
          • op_offset
          • rename_entry
          • strlen
          • get_extra_cmt
          • get_enum_flag
          • fgetc
          • Internal Error
          • op_stkvar
          • get_last_index
          • get_field_ea
          • get_last_struc_idx
          • How to use the help subsystem
          • get_struc_id
          • select_thread
          • create_array
          • get_struc_cmt
          • set_array_string
          • set_func_attr
          • set_storage_type
          • get_struc_size
          • demangle_name
          • get_next_fixup_ea
          • get_next_bmask
          • delattr
          • gen_simple_call_chart
          • patch_qword
          • get_enum_name
          • loader_input_t.getc
          • get_first_struc_idx
          • get_debugger_event_cond
          • read_dbg_qword
          • define_local_var
          • generate_disasm_line
          • add_idc_hotkey
          • tolower
          • del_selector
          • set_debugger_event_cond
          • get_imagebase
          • gen_file
          • get_entry
          • find_custom_data_format
          • get_debug_name_ea
          • add_default_til
          • set_func_end
          • exit_process
          • delete_array
          • xtol
          • get_exception_code
          • detach_process
          • set_enum_cmt
          • get_wide_word
          • put_bookmark
          • is_loaded
          • add_enum_member
          • parse_decls
          • readstr
          • get_entry_qty
          • ord
          • sprintf
          • get_root_filename
          • get_enum_member_cmt
          • create_word
          • set_func_flags
          • loader_input_t.tell
          • create_align
          • read_dbg_dword
          • get_struc_idx
          • next_addr
          • get_bytes
          • batch
          • start_process
          • Cannot Create File
          • process_config_line
          • del_user_info
          • qmakefile
          • set_struc_name
          • print_decls
          • create_custom_data
          • del_enum_member
          • format_cdata
          • get_fixup_target_sel
          • get_item_size
          • loader_input_t.gets
          • get_last_bmask
          • Step Tracing Options
          • get_enum_idx
          • selector_by_name
          • Already recording a macro for...
          • get_enum_cmt
          • next_not_tail
          • prev_head
          • set_color
          • set_numbered_type
          • get_member_name
          • auto_wait
          • get_enum_member_bmask
          • fseek
          • get_segm_start
          • attach_process
          • Trace file functions
          • get_enum_member_value
          • op_stroff
          • get_next_offset
          • set_processor_type
          • get_bookmark_desc
          • Entering String for Search
          • create_data
          • lastattr
          • get_operand_value
          • collect_stack_trace
          • toupper
          • get_fixup_target_dis
          • set_cmt
          • add_entry
          • set_segm_addressing
          • qmake_full_path
          • get_source_linnum
          • fputc
          • resume_thread
          • get_func_attr
          • get_first_enum_member
          • add_sourcefile
          • get_first_bmask
          • read_selection_start
          • hasattr
          • get_member_cmt
          • gen_flow_graph
          • get_array_element
          • get_tinfo
          • loader_input_t
          • tinfo_errstr
          • TRUNC
          • add_segm_ex
          • Not enough memory available to complete operation.
          • Local types information and manipulation helpers
          • set_source_linnum
          • get_next_enum_member
          • loader_input_t.readbytes
          • set_array_params
          • jumpto
          • get_bookmark
          • set_enum_bf
          • prev_not_tail
          • toggle_sign
          • loader_input_t.size
          • Trace events functions
          • get_func_flags
          • get_gotea
          • Bad BIOS & DOS Comments Base
          • set_segm_attr
          • get_item_head
          • set_default_sreg_value
          • print_insn_mnem
          • set_member_cmt
          • get_ordinal_qty
          • set_target_assembler
          • add_user_stkpnt
          • set_local_type
          • Hidden ranges
          • del_items
          • compile_idc_text
          • Dalvik debugger extension functions
          • byte_value
          • create_dword
          • is_code
          • del_func
          • get_enum
          • make_array
          • rotate_left
          • recalc_spd
          • search_path
          • CommonBits
          • get_processor_name
          • set_func_cmt
          • get_prev_bmask
          • Hashes
          • split_sreg_range
          • process_ui_action
          • set_fixup
          • get_fixup_target_type
          • create_oword
          • get_flags
          • get_func_name
          • create_strlit
          • add_struc
          • atol
          • load_debugger
          • mkdir
          • set_struc_idx
          • sizeof
          • get_enum_member_by_name
          • save_database
          • guess_type
          • get_segm_name
          • print_operand
          • qisabspath
          • get_member_qty
          • set_struc_cmt
          • get_fixup_target_flags
          • idadir
          • object.retrieve
          • add_auto_stkpnt
          • get_numbered_type_name
          • get_enum_member_name
          • get_next_index
          • prev_addr
          • get_name_ea
          • get_sp_delta
          • set_bmask_cmt
          • get_struc_qty
          • readlong
          • set_segm_name
          • get_prev_offset
          • set_segm_alignment
          • get_strlit_contents
          • forget_exception
          • get_item_end
          • add_func
          • get_name
          • Asks
          • get_spd
          • Debugger: control
          • get_wide_byte
          • plan_and_wait
          • set_enum_flag
          • RunPythonStatement
          • del_sourcefile
          • get_prev_struc_idx
          • find_selector
          • get_frame_regs_size
          • op_num
          • define_exception
          • create_double
          • create_byte
          • read_selection_end
          • Disk Positioning Error
          • OpTypes
          • op_plain_offset
          • move_segm
          • get_member_id
          • set_segm_combination
          • get_current_thread
          • trim
          • Debugger: options
          • getn_thread
          • get_frame_id
          • typeinfo.print
          • to_ea
          • rebase_program
          • add_struc_member
          • get_exception_qty
          • get_first_index
          • import_type
          • set_segm_type
          • find_custom_data_type
          • get_next_seg
          • find_func_end
          • get_next_struc_idx
          • get_last_enum_member
          • getattr
          • get_frame_size
          • get_screen_ea
          • loader_input_t.read
          • Bad Macro
          • set_reg_value
          • Debugger: modules
          • create_pack_real
          • writestr
          • exec_idc
          • get_enum_size
          • set_enum_name
          • create_tbyte
          • sel2para
          • atoa
          • loader_input_t.close
          • add_enum
          • ltoa
          • set_enum_idx
          • substr
          • del_idc_hotkey
          • Breakpoint handling functions
          • loader_input_t.seek
          • cleanup_appcall
          • object.store
          • get_type
          • qexit
          • get_debug_name
          • get_array_id
          • Can't Open File
          • suspend_process
          • process_config_directive
          • get_entry_name
          • get_last_member
          • get_struc_name
          • clear_selection
          • fclose
          • firstattr
          • How to move/resize windows
          • create_yword
          • dbg_appcall
          • get_qword
          • patch_dword
          • begin_type_updating
          • read_dbg_byte
          • get_fpnum
          • qsleep
          • get_first_member
          • get_nsec_stamp
          • del_stkpnt
          • eval
          • savefile
          • eval_python
          • Xrefs
          • strstr
          • writeshort
          • get_sreg
          • get_segm_end
          • get_func_off_str
          • set_func_start
          • del_array_element
          • get_full_flags
          • set_exception_flags
          • rename_array
          • get_frame_args_size
          • op_flt
          • get_min_spd_ea
          • apply_type
          • get_prev_index
          • loadfile
          • retrieve_input_file_md5
          • get_wide_dword
          • patch_dbg_byte
          • Functions provided by the WinDbg debugger
          • get_original_byte
          • get_member_strid
          • call_system
          • writelong
          • get_thread_qty
          • nextattr
          • send_dbg_command
          • get_first_seg
          • get_processes
          • patch_word
          • get_manual_insn
          • ftell
          • get_entry_ordinal
          • set_array_long
          • delete_all_segments
          • TO_LONG
          • Function chunk related functions
          • Debugger: events
          • get_prev_func
          • op_seg
          • validate_idb_names
          • fprintf
          • fopen
          • strfill
          • del_fixup
          • get_bmask_name
          • Disk Read Error
          • inf_attr
          • is_bf
          • read_dbg_word
          • qdirname
          • get_segm_attr
          • func_contains
          • get_enum_qty
          • del_source_linnum
          • get_sourcefile
          • clr_database_flag
          • bTree Error
          • set_name
          • Refresh Screen
          • op_enum
          • getn_enum
          • get_db_byte
          • setattr
          • get_forced_operand
          • op_bin
          • Functions provided by the replayer debugger
          • prevattr
          • update_extra_cmt
          • get_str_type
          • op_man
          • choose_func
          • set_bmask_name
          • get_curline
          • decode_insn
          • set_segment_bounds
          • get_struc_by_idx
          • set_segm_class
          • write_dbg_memory
          • get_exception_name
          • get_enum_member
          • is_mapped
          • del_enum
          • get_frame_lvar_size
          • get_operand_type
          • set_root_filename
          • compile_idc_file
          • typeinfo.size
          • get_local_tinfo
          • get_fixup_target_off
          • is_union
          • unlink
          • get_segm_by_sel
          • set_enum_width
          • take_memory_snapshot
          • exec_python
          • get_next_func
          • get_member_offset
          • get_func_cmt
          • parse_decl
          • create_qword
          • next_head
          • suspend_thread
          • loader_input_t.getz
          • get_color
          • get_reg_value
          • load_and_run_plugin
          • set_database_flag
          • set_enum_member_name
          • set_member_type
          • get_prev_enum_member
      • IDC examples
        • Batch analysis
        • Device driver analysis
        • New file format definition
        • Structures manipulation
        • VxD analysis
        • Analyzing encrypted code
  • Admin Guide
    • Lumina server
    • Teams server
    • License server
      • Installing on Windows
      • Installing on Linux
      • Installing on OS X
Powered by GitBook
LogoLogo

Need Help?

  • FAQs
  • Support

Community

  • Forum
  • Plugins

Resources

  • Blog
  • Download center

© 2025 Copyright Hex-Rays

On this page
  • Volatile memory
  • Constant memory
  • CONTAINING_RECORD macro
  • Indirect calls

Was this helpful?

Export as PDF
  1. User Guide
  2. Decompiler

Tips and tricks

Last updated 6 months ago

Was this helpful?

First of all, read the page. It explains how to deal with most decompilation problems. Below is a mix of other useful information that did not fit into any other page:

  • more to come...

Volatile memory

Sometimes the decompiler can be overly aggressive and optimize references to volatile memory completely away. A typical situation like the following:

                 device_ready    DCD ? ; VOLATILE!

                                 MOV     R0, =device_ready
                                 LDR     R1, [R0]
                 LOOP:
                                 LDR     R2, [R0]
                                 SUB     R2, R1
                                 BEQ     LOOP
         

can be decompiled into

                 while ( 1 )
                   ;
         

because the decompiler assumes that a variable cannot change its value by itself and it can prove that r0 continues to point to the same location during the loop.

To prevent such optimization, we need to mark the variable as volatile. Currently the decompiler considers memory to be volatile if it belongs to a segment with one of the following names: IO, IOPORTS, PORTS, VOLATILE. The character case is not important.

Constant memory

Sometimes the decompiler does not optimize the code enough because it assumes that variables may change their values. For example, the following code:

                   LDR     R1, =off_45934
                   MOV     R2, #0
                   ADD     R3, SP, #0x14+var_C
                   LDR     R1, [R1]
                   LDR     R1, [R1]        ; int
                   BL      _IOServiceOpen
         

can be decompiled into

                 IOServiceOpen(r0_1, *off_45934, 0)
         

but this code is much better:

                 IOServiceOpen(r0_1, mach_task_self, 0)
         

because

                 off_45934 DCD _mach_task_self
         

is a pointer that resides in constant memory and will never change its value.

The decompiler considers memory to be constant if one of the following conditions hold:

  1. the segment type is CODE

  2. the segment name is one of the following (the list may change in the future): .text, .rdata, .got, .got.plt, .rodata, __text, __const, __const_coal, __cstring, __cfstring, __literal4, __literal8, __pointers, __nl_symbol_ptr, __la_symbol_ptr, __objc_catlist, __objc_classlist, __objc_classname, __objc_classrefs, __objc_const, __objc_data, __objc_imageinfo, __objc_ivar, __objc_methname, __objc_methtype, __objc_protolist, __objc_protorefs, __objc_selrefs, __objc_superrefs, __message_refs, __cls_refs, __inst_meth, __cat_inst_meth, __cat_cls_meth, __OBJC_RO

    The decompiler tries to completely get rid of references to the following segments and replace them by constants: .got, .got.plt, __pointers, __nl_symbol_ptr, __la_symbol_ptr, __objc_ivar, __message_refs, __cls_refs

It is possible to override the constness of an individual item by specifying its type with the volatile or const modifiers.

CONTAINING_RECORD macro

  1. If there is an assignment like this:

                v1 = (structype *)((char *)v2 - num);
            

    it can be converted into

                v1 = CONTAINING_RECORD(v2, structype, fieldname);
            

    by simply confirming the types of v1 and v2. NOTE: the variables types must be specified explicitly. Even if the types are displayed as correct, the user should press Y followed by Enter to confirm the variable type.


  2.             sub     eax, 41Ch
            

    will have the same effect as in the previous point. Please note that it makes sense to confirm the variable types as explained earlier.


  3.             deviceInfo = (_DEVICE_INFO *)((char *)&thisEntry[-131] - 4);
            

    will convert it to:

                deviceInfo = CONTAINING_RECORD(thisEntry, _DEVICE_INFO, ListEntry);
            

    Please note that it makes sense to confirm the variable types as explained earlier.

Indirect calls

Since the arguments of indirect calls are collected before defining variables, specifying the type of the variable that holds the function pointer may not be enough. The user have to specify the function type using other methods in this case. The following methods exist (in the order of preference):

  1. For indirect calls of this form:

                call ds:funcptr
            

    If funcptr is initialized statically and points to a valid function, just ensure a correct function prototype. The decompiler will use it.

  2. For indirect calls of this form:

                call [reg+offset]
            

    If reg points to a structure with a member that is a function pointer, just convert the operand into a structure offset (hotkey T):

                call [reg+mystruct.funcptr]
            

    and ensure that the type of mystruct::funcptr is a pointer to a function of the desired type.

  3. Specify the type of the called function using Edit, Operand type, Set operand type. If the first two methods cannot be applied, this is the recommended method. The operand type has the highest priority, it is always used if present.

  4. If the address of the called function is known, use Edit, Plugins, Change the callee address (hotkey Alt-F11). The decompiler will use the type of the specified callee. This method is available only for x86. For other processors adding a code cross reference from the call instruction to the callee will help.

the segment has access permissions defined but the write permission is not in the list (to change the segment permissions use the "Edit, Segments, Edit Segment" menu item or the built-in function)

The decompiler knows about the macro and tries to use it in the output. However, in most cases it is impossible to create this macro automatically, because the information about the containing record is not available. The decompiler uses three sources of information to determine if CONTAINING_RECORD should be used:

applied to numbers in the disassembly listing are used as a hint to create CONTAINING_RECORD. For example, applying structure offset to 0x41C in

applied to numbers in the decompiler output. For example, applying _DEVICE_INFO structure offset to -131 in the following code:

In most cases the CONTAING_RECORD macro can be replaced by a shorter and nicer expression if a used. In this case it is enough to declare the pointer as a shifted pointer and the decompiler will transform all expressions where it is used.

set_segm_attr
CONTAINING_RECORD
Struct offsets
Struct offsets
shifted pointer
troubleshooting
FPU considerations
Intrinsic functions
Overlapped variables
Volatile memory
Constant memory
CONTAINING_RECORD macro
Indirect calls