Execution Flow
•Step Into -Execute code, step into a
function if one is called
•Step Out -Continue execution until N-1’st
region of stack frame reached
•Step Over -Execute code, execute any
functions that are called without stopping.
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Debugging Pointers and Dynamic Data Structures: Common Problems and Solutions, Slides of Business Administration
An overview of common problems and solutions related to debugging pointers and dynamic data structures in programming. Topics covered include pointer issues such as accessing bogus memory, corrupt data structure segments, data sharing errors, and accessing elements of the wrong type, as well as debugging multitasking programs and using core dumps.
Typology: Slides
2012/2013
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Execution Flow
- Step Into - Execute code, step into a
function if one is called
- Step Out - Continue execution until N-1’st
region of stack frame reached
- Step Over - Execute code, execute any
functions that are called without stopping.
Debugging Pointer and Dynamic
Data Structure Problems
- Pointers and explicitly allocated dynamic
data structures are a central feature in many
popular procedural and object-oriented
languages
- Great power - especially in extreme cases
(eg C/C++)
- Can be very painful to debug
Pointers to Bogus Memory
- Uninitialized pointers
- Failing to check memory allocation errors
- Using stomped pointers corrupted by previous memory operations
- Reminder: Bogus memory access does not necessarily trigger a memory protection fault
- Remedy: Add data type info to dynamic data structures
- Special Case: Indices above/below array space
- Remedy: index checks Docsity.com
Corrupt Data Structure Segments
- Incorrect Adds/Deletes in trees/lists/etc.
- Stomped pointer values from previous memory operations
- Remedy 1: Add type info to dynamic data structures
- Remedy 2: Create routines to check integrity of data structures
- Remedy 3: Flag deleted memory areas
Accessing Elements of Wrong
Type
- Access data element of type x, but think you are accessing one of type y
- Can be a source of frequent headaches depending on application/implementation
- Remedy: Include type info in memory allocations
Accessing Data After Freeing It
- Can be a source of many headaches
- Remedy 1: Include freed flag in memory (not a guaranteed solution
- Remedy 2: Create list of “freed” memory, but do not deallocate it. Check list when dereferencing pointers (very expensive in both time and space)
- Big Brother Problem: Accessing data structure after adding it to a “free” list for quick future reuse
- Remedy: Remedy 1 plus a use counter (also not a guaranteed solution) Docsity.com
Debugging Multitasking
Programs
- Multiple process/multi-threaded code ubiquitous in modern programs
- Many debuggers will work with these programs, but it is not always elegant or easy.
- Fallback method: Put new processes to sleep and then attach a debugger to them before they awake.
- Better solution: Read debugger documentation, find better one if it is weak in this area.
A Few Tips
- Pointers and multithreading together can be
extremely difficult to debug
- Try to debug parts by themselves before
tackling combined system
- Analogous strategies to those used in
pointer debugging can be a big help
- Thread/process timing an important concern