Debugging with GDB (February 2008)
Table Of Contents
- Summary of GDB
- A Sample GDB Session
- Getting In and Out of GDB
- GDB Commands
- Running Programs Under GDB
- Stopping and Continuing
- Examining the Stack
- Examining Source Files
- Examining Data
- Using GDB with Different Languages
- Examining the Symbol Table
- Altering Execution
- GDB Files
- Specifying a Debugging Target
- HP-UX Configuration-Specific Information
- Summary of HP Enhancements to GDB
- HP-UX dependencies
- Supported Platforms and Modes
- HP-UX targets
- Support for Alternate root
- Specifying object file directories
- Fix and continue debugging
- Inline Support
- Debugging Macros
- Debugging Memory Problems
- When to suspect a memory leak
- Memory debugging restrictions
- Memory Debugging Methodologies
- Debugging Memory in Interactive Mode
- Debugging Memory in Batch Mode
- Debugging Memory Interactively After Attaching to a Running Process
- Configuring memory debugging settings
- Scenarios in memory debugging
- Stop when freeing unallocated or deallocated blocks
- Stop when freeing a block if bad writes occurred outside block boundary
- Stop when a specified block address is allocated or deallocated
- Scramble previous memory contents at malloc/free calls
- Detect dangling pointers and dangling blocks
- Detect in-block corruption of freed blocks
- Specify the amount of guard bytes for every block of allocated memory
- Comparison of Memory Debugging Commands in Interactive Mode and Batch Mode
- Heap Profiling
- Memory Checking Analysis for User Defined Memory Management Routines
- Commands to track the change in data segment value
- Thread Debugging Support
- Debugging MPI Programs
- Debugging multiple processes ( programs with fork and vfork calls)
- Debugging Core Files
- Printing the Execution Path Entries for the Current Frame or Thread
- Invoking GDB Before a Program Aborts
- Aborting a Command Line Call
- Instruction Level Stepping
- Enhanced support for watchpoints and breakpoints
- Debugging support for shared libraries
- Language support
- Enhanced Java Debugging Support
- Commands for Examining Java Virtual Machine(JVM) internals
- Support for stack traces in Java, C, and C++ programs
- Support for 64-bit Java, C, aC++ stack unwinding
- Enhanced support for C++ templates
- Support for __fpreg data type on IPF
- Support for _Complex variables in HP C
- Support for debugging namespaces
- Command for evaluating the address of an expression
- Viewing Wide Character Strings
- Support for output logging
- Getting information from a non-debug executable
- Debugging optimized code
- Visual Interface for WDB
- Starting and stopping Visual Interface for WDB
- Navigating the Visual Interface for WDB display
- Specifying foreground and background colors
- Using the X-window graphical interface
- Using the TUI mode
- Changing the size of the source or debugger pane
- Using commands to browse through source files
- Loading source files
- Editing source files
- Editing the command line and command-line history
- Saving the contents of a debugging session to a file
- Support for ddd
- Support for XDB commands
- GNU GDB Logging Commands
- Support for command line calls in a stripped executable
- Displaying the current block scope information
- Linux support
- The HP-UX Terminal User Interface
- XDB to WDB Transition Guide
- By-function lists of XDB commands and HP WDB equivalents
- Overall breakpoint commands
- XDB data formats and HP WDB equivalents
- XDB location syntax and HP WDB equivalents
- XDB special language operators and HP WDB equivalents
- XDB special variables and HP WDB equivalents
- XDB variable identifiers and HP WDB equivalents
- Alphabetical lists of XDB commands and HP WDB equivalents
- Controlling GDB
- Canned Sequences of Commands
- Using GDB under gnu Emacs
- GDB Annotations
- The gdb/mi Interface
- Function and purpose
- Notation and terminology
- gdb/mi Command Syntax
- gdb/mi compatibility with CLI
- gdb/mi output records
- gdb/mi command description format
- gdb/mi breakpoint table commands
- gdb/mi Data manipulation
- gdb/mi program control
- Miscellaneous GDB commands in gdb/mi
- gdb/mi Stack Manipulation Commands
- gdb/mi Symbol query commands
- gdb/mi Target Manipulation Commands
- gdb/mi thread commands
- gdb/mi tracepoint commands
- gdb/mi variable objects
- Reporting Bugs in GDB
- Installing GDB
- Index
176 Debugging with GDB
14.20.4 Privately mapping shared libraries
In cases where you attach to a running program and you try to set a breakpoint in a
shared library, GDB may generate the following message:
The shared libraries were not privately mapped; setting a breakpoint
in a shared library will not work until you rerun the program.
GDB generates this message because the debugger sets breakpoints by replacing an
instruction with a BREAK instruction. The debugger cannot set a breakpoint in a shared
library because doing so can affect other processes on the system in addition to the
process being debugged.
To set the breakpoint you must kill the program and then rerun it so that the dynamic
linker maps a copy of the shared library privately. There are two ways to run the
program:
• Rerun the program under GDB to have the debugger cause dld to map all shared
libraries as private, enabling breakpoint debugging.
• On PA-RISC systems, use the following command on an executable:
‘/opt/langtools/bin/pxdb -s on executable-name ’
The pxdb -s on command marks the executable so that dld maps shared libraries
as private when the program starts up.
You can verify the status of the shared library with this command:
‘/opt/langtools/bin/pxdb -s status executable-name ’
• On both PA-RISC and IA64 systems, use the following command on an executable:
‘chatr +dbg enable executable-name ’
This is similar to the pxdb command described above wherein it directs the dld
to load the shared libraries as private when the program starts up.
14.20.5 Selectively Mapping Shared Libraries As Private
The -mapshared option suppresses mapping all shared libraries in a process private.
This option enables new functions in the dynamic loader (patch PHSSS_33110 or later)
to designate individual shared libraries for debugging. By default, HP WDB instructs
the shared library dynamic loader, dld.sl(5), to map shared libraries in a process
private, regardless of whether the chatr command is run for a particular shlib with
+dbg or not.
The -mapshared option is used to save virtual memory for debugging applications
with large amounts of code in shared libraries on machines with simultaneous debug
sessions. The chatr +dbg option, and the _HP_DLDOPTS environment variable are used
to identify shared libraries for debugging. The -mapshared option ensures that the text
segments of all other shared libraries is shared across the system. The shared libraries
are not mapped private and cannot have breakpoints set in them.
The set mapshared on command can be used to change modes from the (gdb) prompt.
(gdb) set mapshared on
The set mapshared off command can be used to load shared libraries after the current
point is mapped private.