Debugging with gdb The gnu Source-Level Debugger Tenth Edition, for gdb version 8.0.50.20171128-git (GNU Tools for Arm Embedded Processors 7-2017-q4-major) Richard Stallman, Roland Pesch, Stan Shebs, et al. (Send bugs and comments on gdb to http://www.gnu.org/software/gdb/bugs/.) Debugging with gdb TEXinfo 2013-09-11.11 Published by the Free Software Foundation 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA ISBN 978-0-9831592-3-0 Copyright c 1988-2017 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being \Free Software" and \Free Software Needs Free Documentation", with the Front-Cover Texts being \A GNU Manual," and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: \You are free to copy and modify this GNU Man- ual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom." i Table of Contents Summary of gdb :::::::::::::::::::::::::::::::::::: 1 Free Software ::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1 Free Software Needs Free Documentation :::::::::::::::::::::::::::: 1 Contributors to gdb::::::::::::::::::::::::::::::::::::::::::::::::: 3 1 A Sample gdb Session :::::::::::::::::::::::::: 7 2 Getting In and Out of gdb ::::::::::::::::::: 11 2.1 Invoking gdb ::::::::::::::::::::::::::::::::::::::::::::::::: 11 2.1.1 Choosing Files ::::::::::::::::::::::::::::::::::::::::::: 12 2.1.2 Choosing Modes ::::::::::::::::::::::::::::::::::::::::: 13 2.1.3 What gdb Does During Startup :::::::::::::::::::::::::: 16 2.2 Quitting gdb ::::::::::::::::::::::::::::::::::::::::::::::::: 17 2.3 Shell Commands :::::::::::::::::::::::::::::::::::::::::::::: 17 2.4 Logging Output ::::::::::::::::::::::::::::::::::::::::::::::: 18 3 gdb Commands :::::::::::::::::::::::::::::::: 19 3.1 Command Syntax ::::::::::::::::::::::::::::::::::::::::::::: 19 3.2 Command Completion :::::::::::::::::::::::::::::::::::::::: 19 3.3 Getting Help :::::::::::::::::::::::::::::::::::::::::::::::::: 22 4 Running Programs Under gdb ::::::::::::::: 25 4.1 Compiling for Debugging :::::::::::::::::::::::::::::::::::::: 25 4.2 Starting your Program :::::::::::::::::::::::::::::::::::::::: 26 4.3 Your Program's Arguments ::::::::::::::::::::::::::::::::::: 30 4.4 Your Program's Environment:::::::::::::::::::::::::::::::::: 30 4.5 Your Program's Working Directory :::::::::::::::::::::::::::: 31 4.6 Your Program's Input and Output :::::::::::::::::::::::::::: 32 4.7 Debugging an Already-running Process :::::::::::::::::::::::: 33 4.8 Killing the Child Process :::::::::::::::::::::::::::::::::::::: 34 4.9 Debugging Multiple Inferiors and Programs:::::::::::::::::::: 34 4.10 Debugging Programs with Multiple Threads :::::::::::::::::: 37 4.11 Debugging Forks ::::::::::::::::::::::::::::::::::::::::::::: 41 4.12 Setting a Bookmark to Return to Later::::::::::::::::::::::: 43 4.12.1 A Non-obvious Benefit of Using Checkpoints::::::::::::: 45 ii Debugging with gdb 5 Stopping and Continuing ::::::::::::::::::::: 47 5.1 Breakpoints, Watchpoints, and Catchpoints ::::::::::::::::::: 47 5.1.1 Setting Breakpoints :::::::::::::::::::::::::::::::::::::: 48 5.1.2 Setting Watchpoints:::::::::::::::::::::::::::::::::::::: 54 5.1.3 Setting Catchpoints :::::::::::::::::::::::::::::::::::::: 56 5.1.4 Deleting Breakpoints ::::::::::::::::::::::::::::::::::::: 61 5.1.5 Disabling Breakpoints :::::::::::::::::::::::::::::::::::: 62 5.1.6 Break Conditions::::::::::::::::::::::::::::::::::::::::: 63 5.1.7 Breakpoint Command Lists :::::::::::::::::::::::::::::: 64 5.1.8 Dynamic Printf :::::::::::::::::::::::::::::::::::::::::: 66 5.1.9 How to save breakpoints to a file ::::::::::::::::::::::::: 67 5.1.10 Static Probe Points ::::::::::::::::::::::::::::::::::::: 67 5.1.11 \Cannot insert breakpoints"::::::::::::::::::::::::::::: 69 5.1.12 \Breakpoint address adjusted..." :::::::::::::::::::::::: 69 5.2 Continuing and Stepping :::::::::::::::::::::::::::::::::::::: 70 5.3 Skipping Over Functions and Files :::::::::::::::::::::::::::: 73 5.4 Signals:::::::::::::::::::::::::::::::::::::::::::::::::::::::: 76 5.5 Stopping and Starting Multi-thread Programs ::::::::::::::::: 79 5.5.1 All-Stop Mode ::::::::::::::::::::::::::::::::::::::::::: 79 5.5.2 Non-Stop Mode :::::::::::::::::::::::::::::::::::::::::: 80 5.5.3 Background Execution ::::::::::::::::::::::::::::::::::: 81 5.5.4 Thread-Specific Breakpoints :::::::::::::::::::::::::::::: 82 5.5.5 Interrupted System Calls ::::::::::::::::::::::::::::::::: 83 5.5.6 Observer Mode::::::::::::::::::::::::::::::::::::::::::: 84 6 Running programs backward ::::::::::::::::: 87 7 Recording Inferior's Execution and Replaying It :::::::::::::::::::::::::::::::::::::::::::::: 89 8 Examining the Stack :::::::::::::::::::::::::: 97 8.1 Stack Frames ::::::::::::::::::::::::::::::::::::::::::::::::: 97 8.2 Backtraces :::::::::::::::::::::::::::::::::::::::::::::::::::: 98 8.3 Selecting a Frame :::::::::::::::::::::::::::::::::::::::::::: 100 8.4 Information About a Frame :::::::::::::::::::::::::::::::::: 101 8.5 Management of Frame Filters.:::::::::::::::::::::::::::::::: 102 iii 9 Examining Source Files :::::::::::::::::::::: 105 9.1 Printing Source Lines :::::::::::::::::::::::::::::::::::::::: 105 9.2 Specifying a Location :::::::::::::::::::::::::::::::::::::::: 106 9.2.1 Linespec Locations :::::::::::::::::::::::::::::::::::::: 106 9.2.2 Explicit Locations::::::::::::::::::::::::::::::::::::::: 107 9.2.3 Address Locations::::::::::::::::::::::::::::::::::::::: 108 9.3 Editing Source Files:::::::::::::::::::::::::::::::::::::::::: 108 9.3.1 Choosing your Editor ::::::::::::::::::::::::::::::::::: 109 9.4 Searching Source Files ::::::::::::::::::::::::::::::::::::::: 109 9.5 Specifying Source Directories ::::::::::::::::::::::::::::::::: 109 9.6 Source and Machine Code :::::::::::::::::::::::::::::::::::: 112 10 Examining Data::::::::::::::::::::::::::::: 117 10.1 Expressions ::::::::::::::::::::::::::::::::::::::::::::::::: 119 10.2 Ambiguous Expressions ::::::::::::::::::::::::::::::::::::: 120 10.3 Program Variables :::::::::::::::::::::::::::::::::::::::::: 121 10.4 Artificial Arrays :::::::::::::::::::::::::::::::::::::::::::: 124 10.5 Output Formats :::::::::::::::::::::::::::::::::::::::::::: 124 10.6 Examining Memory ::::::::::::::::::::::::::::::::::::::::: 126 10.7 Automatic Display :::::::::::::::::::::::::::::::::::::::::: 128 10.8 Print Settings::::::::::::::::::::::::::::::::::::::::::::::: 130 10.9 Pretty Printing ::::::::::::::::::::::::::::::::::::::::::::: 138 10.9.1 Pretty-Printer Introduction :::::::::::::::::::::::::::: 138 10.9.2 Pretty-Printer Example :::::::::::::::::::::::::::::::: 139 10.9.3 Pretty-Printer Commands:::::::::::::::::::::::::::::: 139 10.10 Value History:::::::::::::::::::::::::::::::::::::::::::::: 140 10.11 Convenience Variables ::::::::::::::::::::::::::::::::::::: 141 10.12 Convenience Functions::::::::::::::::::::::::::::::::::::: 144 10.13 Registers :::::::::::::::::::::::::::::::::::::::::::::::::: 146 10.14 Floating Point Hardware::::::::::::::::::::::::::::::::::: 148 10.15 Vector Unit:::::::::::::::::::::::::::::::::::::::::::::::: 148 10.16 Operating System Auxiliary Information ::::::::::::::::::: 148 10.17 Memory Region Attributes::::::::::::::::::::::::::::::::: 150 10.17.1 Attributes :::::::::::::::::::::::::::::::::::::::::::: 151 10.17.1.1 Memory Access Mode :::::::::::::::::::::::::::: 151 10.17.1.2 Memory Access Size:::::::::::::::::::::::::::::: 152 10.17.1.3 Data Cache :::::::::::::::::::::::::::::::::::::: 152 10.17.2 Memory Access Checking ::::::::::::::::::::::::::::: 152 10.18 Copy Between Memory and a File ::::::::::::::::::::::::: 152 10.19 How to Produce a Core File from Your Program ::::::::::: 153 10.20 Character Sets::::::::::::::::::::::::::::::::::::::::::::: 154 10.21 Caching Data of Targets ::::::::::::::::::::::::::::::::::: 157 10.22 Search Memory :::::::::::::::::::::::::::::::::::::::::::: 158 10.23 Value Sizes :::::::::::::::::::::::::::::::::::::::::::::::: 159 11 Debugging Optimized Code :::::::::::::::: 161 11.1 Inline Functions :::::::::::::::::::::::::::::::::::::::::::: 161 11.2 Tail Call Frames :::::::::::::::::::::::::::::::::::::::::::: 162 iv Debugging with gdb 12 C Preprocessor Macros::::::::::::::::::::: 165 13 Tracepoints :::::::::::::::::::::::::::::::::: 169 13.1 Commands to Set Tracepoints :::::::::::::::::::::::::::::: 169 13.1.1 Create and Delete Tracepoints ::::::::::::::::::::::::: 170 13.1.2 Enable and Disable Tracepoints :::::::::::::::::::::::: 172 13.1.3 Tracepoint Passcounts ::::::::::::::::::::::::::::::::: 172 13.1.4 Tracepoint Conditions:::::::::::::::::::::::::::::::::: 173 13.1.5 Trace State Variables :::::::::::::::::::::::::::::::::: 173 13.1.6 Tracepoint Action Lists :::::::::::::::::::::::::::::::: 174 13.1.7 Listing Tracepoints :::::::::::::::::::::::::::::::::::: 176 13.1.8 Listing Static Tracepoint Markers :::::::::::::::::::::: 177 13.1.9 Starting and Stopping Trace Experiments :::::::::::::: 178 13.1.10 Tracepoint Restrictions ::::::::::::::::::::::::::::::: 180 13.2 Using the Collected Data ::::::::::::::::::::::::::::::::::: 181 13.2.1 tfind n:::::::::::::::::::::::::::::::::::::::::::::::: 181 13.2.2 tdump:::::::::::::::::::::::::::::::::::::::::::::::::: 183 13.2.3 save tracepoints filename ::::::::::::::::::::::::::: 184 13.3 Convenience Variables