About debuginfod
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debuginfod is a service for software developers. It helps with diagnosing issues in software and centralises the storage of debug symbols, source code, etc.
One of the main advantages to debuginfod is that debugging information can be retrieved on-demand for packages shipped with Ubuntu without the need to manually install the debug symbol packages.
Ubuntu maintains its own debuginfod service, which regularly indexes the debug symbols present in ddebs and other packages and serves this information over HTTPS.
Currently, the service only provides DWARF information. There are plans for it to also index and serve source-code in the future.
Using the service
debuginfod is indexing ddebs packages from all supported Ubuntu releases. Once a release goes unsupported, we stop indexing ddebs from it and eventually stop serving debug symbols for its packages.
From Kinetic onwards, when you install GNU Debugger (GDB) your system will be automatically configured to use Ubuntu’s debuginfod service. For previous Ubuntu releases, you can manually enable the service by setting the DEBUGINFOD_URLS environment variable in your shell. If you use Bash, you can do that by adding the following snippet to your ~/.bashrc:
export DEBUGINFOD_URLS="https://debuginfod.ubuntu.com"
When you run GDB, and if you have the DEBUGINFOD_URLS variable in your environment, you will be asked whether you would like to use the service. If you want to make sure that GDB always uses debuginfod, you can put the following snippet inside your ~/.gdbinit file:
set debuginfod enabled on
The debug symbol files will be downloaded on-the-fly during your debugging session, and will be saved locally inside the $XDG_CACHE_HOME/.debuginfod_client/ directory. If $XDG_CACHE_HOME is empty, then ~/.cache/debuginfod_client is used instead.
You can safely remove this directory or any files inside it; they will only be downloaded again if and when they are needed.
Example session with GDB
If you have enabled use of debuginfod on your system, here is what happens when you invoke GDB to debug a binary from an Ubuntu package:
$ gdb -q program
Reading symbols from program...
This GDB supports auto-downloading debuginfo from the following URLs:
https://debuginfod.ubuntu.com
Enable debuginfod for this session? (y or [n])
When you answer y to the question above, GDB will download the debug symbols for program:
Enable debuginfod for this session? (y or [n]) y
Debuginfod has been enabled.
To make this setting permanent, add 'set debuginfod enabled on' to .gdbinit.
Downloading 0.20 MB separate debug info for /home/ubuntu/program
Reading symbols from /home/ubuntu/.cache/debuginfod_client/c0fbda15a807f880e9d0b2dcc635eeeb1f0f728e/debuginfo...
(gdb)
Opting out of the service
If, for some reason, you prefer not to use the service, you can opt-out of it by un-setting the DEBUGINFOD_URLS environment variable. This can be done by putting the following snippet inside your shell’s configuration file:
unset DEBUGINFOD_URLS
You can also disable GDB’s willingness to use debuginfod by putting the following snippet inside your ~/.gdbinit:
set debuginfod enabled off
How does debuginfod find the debug symbols for the binary I am debugging?
debuginfod relies on a unique hash that identifies binaries and shared libraries called Build-ID. This 160-bit SHA-1 hash is generated by the compiler, and can be consulted using tools like readelf:
$ readelf -n /usr/bin/bash
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000020 NT_GNU_PROPERTY_TYPE_0
Properties: x86 feature: IBT, SHSTK
x86 ISA needed: x86-64-baseline
Displaying notes found in: .note.gnu.build-id
Owner Data size Description
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: 3e770d2cd0302c6ff2a184e8d2bf4ec98cfcded4
Displaying notes found in: .note.ABI-tag
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 3.2.0
When you are debugging a program, GDB will send the program’s Build-ID to the debuginfod server, which will check if it has the corresponding debug information for that binary/library. If it does, then it will send the debug symbols via HTTPS back to GDB.
Can ddebs packages co-exist with debuginfod?
Yes. GDB will try to use local debug information if available. That means that if you have a ddeb package installed that provides the necessary debug symbols for the program being debugged (or if you have already downloaded that information from the debuginfod service earlier), then GDB will use it in favour of performing the download.
Can I use debuginfod with my own binary that links against system libraries?
Yes! debuginfod will not be able to provide any debug symbols for your own program, but it will happily serve debug information for any system libraries that your program links against.