Gdb For Mac
Posted : admin On 11/14/2019You can debug a C or C++ program using GDB,the GNU debugger, which was developed by the sameorganization that released Emacs. You can easily integrateit with Emacs to interactively debug programs. While you can use itfrom the Unix prompt, it has additional functionality whenyou use it within the Emacs editor.
I got gdb working on Mojave by: a) getting the latest gdb source archive (at time of writing, ftp://sourceware.org/pub/gdb/snapshots/current/gdb-weekly-8.2.50. GDB in batch mode now exits with status 1 if the last executed command failed. Support for building GDB with GCC's Undefined Behavior Sanitizer. See the NEWS file for a more complete and detailed list of what this release includes. February 27th, 2019: GDB 8.3 branch created. The GDB 8.3 branch (gdb-8.3-branch) has been created. To check out a. Tutorial of gcc and gdb. The graphical user interface (GUI) domainates the current operating environments for personal computing. However, there are still tons of powerful tools, such as gcc and gdb, using the traditional text-based interface. GDB: The GNU Project Debugger GDB Maintainers contributing current git documentation mailing lists Download GDB The most recent. GDB 8.1 is broken on macOS 10.13. Bug 1, Bug 2. You need to downgrade to 8.0 for the time being, see this answer on how to do that. I had to run 10. Above with sudo.
Gdb Macro
Compile program with appropriate debugging flag(s)
Assume you have the following program, foo.c
, that issegfaulting:
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To use GDB, first compile your program using the-g
option in cc
orgcc
, for example:
Open GDB (within Emacs for added functionality)
- While editing
foo.c
within Emacs, to start a separatewindow for the debugger and to load the executable, enter:When Emacs prompts you, enter:
You should get a
(gdb)
prompt similar to this: - You can list source code using the
list
command. (Thelist
command with two comma-separated integer parameterswill show code between those two line numbers, for example,list1, 6
). - To investigate why the program is crashing, run the program firstusing the
run
command. Then, you could try thewhere
command. It will show you a stack trace, with thesource line number where each function in the stack was.Note: The
run
command will cause yoursource code to be loaded in a second window, one of the manyadvantages of using GDB within Emacs.In this simple case, it is obvious that the program crashed on the
memset()
function call. - In real world programs with more complicated code, if the
where
command is not enough to isolate the problem,you'll need to do debugging at a more detailed level.For that, you may need to set break points at spots where you thinkthe problem might be. In the example shown below, break points are setat line numbers 3, 4, and 6. Then, the program is run once again,while stepping through each break point using the
run
andnext
commands respectively:Given that the example was too simple in the first place, it shouldstill be obvious that the call to
memset ()
is what wascausing the segfault. - Once you find the bug, you might want to kill the program (thatcrashed halfway through) using the
kill
command: - You can get help within GDB using the
help
command;enteringhelp
by itself will list a set of subtopics forwhich help is available:Entering
help topic
will show you more detailedinformation, for example:
This document explains how to debug Mozilla-derived applications such as Firefox, Thunderbird, and SeaMonkey on macOS using Xcode. If you want to debug from the terminal see Debugging Mozilla with lldb. For specific information on a way to debug hangs, see Debugging a hang on OS X.
Creating a debuggable build
First, you need to build the application you're going to debug using --disable-optimize
--enable-debug-symbols
in your .mozconfig (also add --enable-debug
if you want assertions etc. compiled in). See Building Firefox for macOS if you need help creating your own build.
Debugging Firefox on macOS 10.14+
macOS 10.14 introduced Notarization and Hardened Runtime features for improved application security. macOS 10.15 went further, requiring applications to be Notarized with Hardened Runtime enabled in order to launch (ignoring workarounds.) When run on earlier macOS versions, Notarization and Hardened Runtime settings have no effect.
Official Builds
At this time, official builds of Firefox 69 and later are Notarized. Uplifts to Firefox 68 and ESR 68 to enable Notarization are planned. As a result, it is not possible to attach a debugger to these official Firefox releases on macOS 10.14+ without disabling System Integrity Protection (SIP). This is due to Notarization requiring Hardened Runtime to be enabled with the com.apple.security.get-task-allow
entitlement disallowed. Rather than disabling SIP (which has security implications), it is recommended to debug with try builds or local builds. The differences are explained below.
try Server Builds
In most cases, developers needing to debug a build as close as possible to the production environment should use a try build. These builds enable Hardened Runtime and only differ from production builds in that they are not Notarized which should not otherwise affect functionality, (other than the ability to easily launch the browser on macOS 10.15+ -- see quarantine note below). At this time, developers can obtain a Hardened Runtime build with the com.apple.security.get-task-allow
entitlement allowed by submitting a try build and downloading the dmg generated by the 'Rpk' shippable build job. A debugger can be attached to Firefox processes of these builds. try builds use the developer.entitlements.xml
file from the source tree while production builds use production.entitlements.xml
. On macOS 10.15+, downloaded try builds will not launch by default because Notarization is required. To workaround this problem, remove the quarantine extended attribute from the downloaded Nightly:
 $ xattr -r -d com.apple.quarantine /Path/to/Nightly.app
Local Builds
Local builds of mozilla-central do not enable Hardened Runtime and hence do not have debugging restrictions. As a result, some functionality will be permitted on local builds, but blocked on production builds which have Hardened Runtime enabled. Bug 1522409 was filed to automate codesigning local builds to enable Hardened Runtime by default and eliminate this discrepancy.
To obtain a Hardened Runtime build without using try infrastructure, a developer can manually codesign builds using the macOS codesign(1)
command with the developer.entitlements.xml
file from the tree. This requires creating a codesigning identity.
Disabling System Integrity Protection (SIP)
If debugging a production build is required, follow Apple's documented steps for disabling System Integrity Protection (SIP). Note that disabling SIP bypasses Hardened Runtime restrictions which can mask some bugs that only occur with Hardened Runtime so it is recommended to test fixes with SIP enabled. Disabling SIP has system security implications that should be understood before taking this step.
Creating an Xcode project
If you try to create a new Xcode project in an existing directory then Xcode will delete its existing contents (Xcode will warn you beforehand). To work around that the steps below will have you initialize the project outside the Mozilla source tree, close the project, copy the .xcodeproj project 'file' into the source tree, and only then will you reopen the project to finish setting it up.
Note also that since Xcode 7.3.1 it doesn't seem to be possible to have the Xcode project live outside the source tree. If you try to do that then Xcode will simply copy the source files under the project directory rather than link to them (still the case in Xcode 10?) which breaks debugging and the possibility to modify-rebuild-relaunch from inside Xcode.
These steps were last updated for Xcode 10:
- Open Xcode, and create a new Project with File > New Project. Select the 'Cross-platform' tab then under the 'Other' template group select the 'Empty' project type. the click Next. Name the project and click Next. Select a temporary directory to create the project files in and then click Create.
- Before going any further, close the project (File > Close Project) and open Finder. Find the *.xcodejproj directory in the temporary directory, move it into your Mozilla source tree, and then double-click on it to open it.
- In the left-hand pane in Xcode you should see a tree where the root item has the project name, and under it is the temporary directory that you originally created the Xcode project in under. Right click on the temporary directory and delete it, then right click on the root item, select 'Add files to '<project-name>', select all the files and directories in your source directory, then click Add. (These will then be progressively added under the root item <project-name> in the left-hand pane. Note that subdirectories may initially appear to be empty, but they too will progressively be populated as Xcode processes the sourse files. Once done, you should be able to open any file quickly by hitting Cmd-Shift-O and typing in the name of a file.)
- In the Product menu, select Scheme > New Scheme and name your scheme (for example, 'Debug'). After you click OK, Xcode should open the settings window for the new scheme. (If not, then open its settings from the Product > Edit Scheme menu.)
- Select 'Run' on the left-hand side of the settings window, then select the 'Info' tab. Set the Executable by clicking on 'None' and selecting 'Other..'. A new dialog titled 'Choose an executable to launch' will pop up. Browse to the
.app
file that you want to debug (Firefox.app
,Nightly
Debug.app
etc). The.app
file is typically found inside thedist
folder in your build directory. - If you are debugging Firefox, Thunderbird, or some other application that supports multiple profiles, using a separate profile for debugging purposes is recommended. See 'Having a profile for debugging purposes' below. Select the 'Arguments' tab in the scheme editor, and click the '+' below the 'Arguments passed on launch' field. Add '-P profilename', where profilename is the name of a profile you created previously. Repeat that to also add the argument '-no-remote'.
- Also in the 'Arguments' panel, you may want to add an environment variable MOZ_DEBUG_CHILD_PROCESS set to the value 1 to help with debugging e10s.
- Select 'Build' from the left of the scheme editor window, and check that there is nothing listed under Targets (otherwise it may cause problems when you try to run the executable for debugging since you will get build errors).
- Click 'Close' to close the scheme editor.
At this point you can run the application from Xcode, and when you pause or hit breakpoints it should show open the correct source file at the correct line.
Setting up lldb
lldb is the debugger XCode version 5 and above uses under the hood (previous versions used gdb).
The .lldbinit file in the source tree imports many useful Mozilla specific lldb settings and commands but when debugging in XCode this file is not loaded by default since Xcode does not run using $topsrcdir as its current working directory (see bug 942133). To work around this add the following to $HOME/.lldbinit
and set fallbacktopsrcdir
to a Mozilla source directory that you regularly update:
Mac Mojave Gdb
see Debugging Mozilla with lldb for more information.
Note that one important issue that the Mozilla .lldbinit file fixes is that by default some breakpoints will be listed as 'pending', and XCode will not stop at them. If you don't include the Mozilla's .lldbinit, you must at least put settings set target.inline-breakpoint-strategy always
in your $HOME/.lldbinit
as recommended on Debugging Mozilla with lldb.
You will need to use Python v2.x supplied by macOS, otherwise, you will encounter this error: ImportError: cannot import name _remove_dead_weakref
. Run the following to correct this: brew unlink python@2
.
Having a profile for debugging purposes
It is recommended to create a separate profile to debug with, whatever your task, so that you don't lose precious data like Bookmarks, saved passwords, etc. So that you're not bothered with the profile manager every time you start to debug, expand the 'Executables' branch of the 'Groups & Files' list and double click on the Executable you added for Mozilla. Click the plus icon under the 'Arguments' list and type '-P <profile name>' (e.g. '-P MozillaDebug'). Close the window when you're done.
Running a debug session
Make sure breakpoints are active (which implies running under the debugger) by opening the Product menu and selecting 'Debug / Activate Breakpoints' (also shown by the 'Breakpoints' button in the top right section of the main window). Then click the 'Run' button or select 'Run' from the Product menu.
Setting breakpoints
Setting a breakpoint is easy. Just open the source file you want to debug in Xcode, and click in the margin to the left of the line of code where you want to break.
During the debugging session, each time that line is executed, the debugger will break there, and you will be able to debug it.
Note that with the default configuration, some breakpoints will be listed as 'pending', and XCode will not stop at them. If you don't include the Mozilla's .lldbinit, you must at least put settings set target.inline-breakpoint-strategy always
in your $HOME/.lldbinit
as recommended on Debugging Mozilla with lldb.
Using Mozilla-specific lldb commands
If you included the .lldbinit when Setting up lldb, you can use Mozilla-specific lldb commands in the console, located in the Debug area of XCode. For example, type js
to see the JavaScript stack. For more information, see Debugging Mozilla with lldb.
Debugging e10s child processes
Using XCode to debug child processes created by an e10s-enabled browser is a little trickier than debugging a single-process browser, but it can be done. These directions were written using XCode 6.3.1
- Complete all the steps above under 'Creating the Project'
- From the 'Product' menu, ensure the scheme you created is selected under 'Scheme', then choose 'Scheme > Edit Scheme'
- In the resulting popup, click 'Duplicate Scheme'
- Give the resulting scheme a more descriptive name than 'Copy of Scheme'
- Select 'Run' on the left-hand side of the settings window, then select the 'Info' tab. Set the Executable by clicking on the 'Executable' drop-down, and selecting the
plugin-container.app
that is inside the app bundle of the copy of Firefox you want to debug. - On the same tab, under 'Launch' select 'Wait for executable to be launched'
- On the 'Arguments' tab, remove all arguments passed on launch.
Now you're ready to start debugging:
- From the 'Product' menu, ensure the scheme you created above is selected under 'Scheme'
- Click the 'Run' button. The information area at the top of the window will show 'Waiting for plugin-container to launch'
- From a command line, run your build of Firefox. When that launches a child process (for example, when you start to load a webpage), XCode will notice and attach to that child process. You can then debug the child process like you would any other process.
- When you are done debugging, click the 'Stop' button and quit the instance of Firefox that you were debugging in the normal way.
Gdb For Mac Os Mojave
For some help on using lldb see Debugging Mozilla with lldb.
Gdb Macos Mojave
Other resources
Apple has an extensive list of debugging tips and techniques.
Questions? Problems?
Try asking in our IRC channels #developers or #macdev.