Debugging

lastmod 2025-03-08created 2017-01-3027 edits

Debug (debug), debugging (debugging), or fixing refers to the testing process of finding errors in the correctness or logic (bugs) of a computer program. It is also called debugging (debugging) or fixing. Common debugging methods include checks during testing, testing with machines, and testing with real data.

Binary Tools

• [Recommended] Understanding what a Linux binary is doing ¹
• [Recommended] UNIX as IDE: 6. Debugging (strace, ltrace)

A set of tools for binary debugging:

• strings
• file
• objdump
• strace - monitors system commands
• ltrace - monitors library calls
• gdb
• sysdig
• ldd
• size
• readelf
• nm
• pmap - view memory allocation details

GUI Disassembler

• Hopper (commercial)
• hex-rays (commercial)
• Cutter (Open Source)
• radare2 (Open Source)

Tip/Trick

Python gdb debugging

See Gdb#Python gdb debugging.

Finding the crash location

• Debugging tip: finding where a program crashes on Linux
• (gdb) The GNU Debugger : 3. Analyzing Stack information

Find the address where the crash occurred, then use addr2line to locate it.

Example:

$ addr2line -fe a.out 0x8048767

Segfault debugging

• How to get a core dump for a segfault on Linux
• (basics only) How to find Segmentation Error in C & C++ ? (Using GDB)
• (basics only) 7.2 Example Debugging Session: Segmentation Fault Example
• Obtaining a stack trace in C upon SIGSEGV (Chinese site, good content. Refer to the PDF if possible: Obtaining_a_stack_trace_in_C_upon_SIGSEGV.pdf)
• How to debug a GCC segmentation fault - GNU Project - Free Software Foundation (FSF)

Configure GCC with --enable-checking. Compile it with -g -O0 so that you can use gdb.

Compile your test case with -v -da -Q.

• -Q: will show which function in the test case is causing it to crash.
• -v: shows how cc1 was invoked (useful for invoking cc1 manually in gdb).
• -da: dumps the RTL to a file after each stage.

Next, use gdb to get a stack trace:

bash$ gdb cc1
gdb> run arguments
(cc1 will stop at the segmentation fault)
gdb> where
gdb> list

Print out the values of interesting variables, e.g., the ones in the statement which got the segmentation fault. You can use the pt and pr macros from the gdbinit.in file to display GCC data. For example, if there is a value of type tree named t, and a value of type rtx named r, you can use these commands:

gdb> source .gdbinit
gdb> print t
gdb> pt
gdb> print r
gdb> pr
gdb> pt

See also

• Valgrind
• memwatch
• YAMD
• rmdebug
• Dmalloc
• mtrace
• Breakpoint
• addr2line
• gdb
• lldb
• DebugView
• CodeTracer - a time-traveling debugger written in Nim and Rust

Favorite site

• Wikipedia (en) Debugging
• Debugging - ArchWiki

Tip & Guide

• How to debug when a segmentation fault occurs
• Debugging when a Segmentation Fault occurs
• Debugging tip: finding where a program crashes on Linux
• How to debug with the address when a Segmentation fault occurs
• Introducing GEF – GDB Enhanced Features
• Linux Exploits made easy – using the peda debugger
• Debugging B2G using GDB and related Tools

MSVC

• Finding crash point using the MAP file

Guide

• Implementing backtrace through stack walking ²
• Tools for dynamically tracing programs ³
• Friends for memory debugging ⁴

References