Launching zxdb on Fuchsia is as simple as one command:
ffx debug connect
When the debugger is launched, it should show
Connecting (use "disconnect" to cancel)... Connected successfully. 👉 To get started, try "status" or "help". [zxdb]
It'll work 95% of the time, regardless of whether you work in-tree or out-of-tree, using an emulator or a hardware device. If it doesn't work as expected, please check the troubleshooting below.
The build type is compatible
Debuggers on Fuchsia depend on privileged syscalls, most notably
These syscalls are only enabled when the kernel flag
is set to
true, which means debuggers are not available for
If you are building from source, most probably these syscalls are enabled.
zxdb and debug_agent are built
Zxdb depends on an on-target component debug_agent. Both of them are built by default in the
product type. If you are building from source, check whether there's
out/<build_dir>/host_x64/zxdb. If you don't have the debugger in your build, add
//bundles:tools to your "universe", either with:
fx <normal_stuff_you_use> --with //bundles:tools
Or you can edit your GN args directly by editing
<build_dir>/args.gn and adding to the bottom:
universe_package_labels += [ "//bundles:tools" ]
ffx can talk with the device
Make sure that ffx can discover the device, either a emulator or a hardware device, and RCS is started on the device.
$ ffx target list NAME SERIAL TYPE STATE ADDRS/IP RCS demo-emu <unknown> core.qemu-x64 Product [10.0.2.15, Y fec0::90e:486e:b6b5:9780, fec0::487b:fabd:20fa:43ee, 127.0.0.1]
Package server is running
For most build configurations, the debug agent will be in the "universe" (i.e. "available to use") but not in the base build so won't be on the system before boot. You will need to run:
Debug symbols are registered
Zxdb will by default obtain the locations of the debug symbols from the
The registrations of debug symbols from in-tree and most out-of-tree environments are automated.
In case these doesn't work out, there are three command-line flags in zxdb to provide additional
symbol lookup locations for zxdb:
--ids-txt, and a general
They all have the corresponding settings that can be manipulated using
For example, to add a ".build-id" directory, either use
ffx debug connect -- --build-id-dir some/other_location/.build-id
Or add it to the
build-id-dirs list option in the interactive UI:
[zxdb] set build-id-dirs += some/other_location/.build-id
For in-tree development,
ffx debug connect automatically sets up all necessary
Some builds produce a
.build-id directory. Symbol files in it are already indexed according to
their build IDs. For example, the Fuchsia build itself makes a
.build-id directory inside the
build directory, e.g.,
out/x64/.build-id. They can be added to zxdb by
command-line flag or
build-id-dirs setting. This is the best option.
Instead of a
.build-id directory, some builds produce a file called
ids.txt that lists build IDs
and local paths to the corresponding binaries. They can be added to zxdb by
ids-txts setting. This is the second-best option.
--symbol-path flag can be used to add arbitrary files or directories to symbol index.
If the path is pointing to a file, it will be treated as an ELF file and added to the symbol index.
If it's a directory, all binaries under the given path are indexed.
Source code location is correctly set up
The Fuchsia build generates symbols relative to the build directory so relative paths look like
../../src/my_component/file.cc). The build directory is usually provided by the symbol index.
If your files are not being found with the default build directories, you will need to provide a build directory to locate the files. This build directory does not need have been used to build, it just needs to produce correct absolute paths when concatenated with the relative paths from the symbol file.
You can add additional build directories on the command line:
ffx debug connect -- --build-dir /home/me/fuchsia/out/x64
Or interactively from within the debugger:
[zxdb] set build-dirs += /home/me/fuchsia/out/x64
If debugger is finding the wrong file, you can replace the entire build directory list by omitting
[zxdb] set build-dirs /home/me/fuchsia/out/x64
If your build produces DWARF symbols with absolute file paths the files must be in that location on
the local system. Absolute file paths in the symbols are not affected by the build search path.
Clang users should use the
-fdebug-prefix-map, which will also help with build hermeticity.