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Previously, we got debug symbols implicitly because we were using `separateDebugInfo = true`, which adds `-ggdb` to the compiler flags.
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Debugging Nix
This section shows how to build and debug Nix with debug symbols enabled.
Additionally, see Testing Nix for further instructions on how to debug Nix in the context of a unit test or functional test.
Building Nix with Debug Symbols
In the development shell, mesonBuildType is set automatically to debugoptimized. This builds Nix with debug symbols, which are essential for effective debugging.
It is also possible to build without optimization for faster build:
[nix-shell]$ NIX_HARDENING_ENABLE=$(printLines $NIX_HARDENING_ENABLE | grep -v fortify)
[nix-shell]$ export mesonBuildType=debug
(The first line is needed because fortify hardening requires at least some optimization.)
Building Nix with sanitizers
Nix can be built with Address and UB sanitizers using LLVM or GCC. This is useful when debugging memory corruption issues.
[nix-shell]$ export mesonBuildType=debugoptimized
[nix-shell]$ appendToVar mesonFlags "-Dlibexpr:gc=disabled" # Disable Boehm
[nix-shell]$ appendToVar mesonFlags "-Dbindings=false" # Disable nix-perl
[nix-shell]$ appendToVar mesonFlags "-Db_sanitize=address,undefined"
Debugging the Nix Binary
Obtain your preferred debugger within the development shell:
[nix-shell]$ nix-shell -p gdb
On macOS, use lldb:
[nix-shell]$ nix-shell -p lldb
Launching the Debugger
To debug the Nix binary, run:
[nix-shell]$ gdb --args ../outputs/out/bin/nix
On macOS, use lldb:
[nix-shell]$ lldb -- ../outputs/out/bin/nix
Using the Debugger
Inside the debugger, you can set breakpoints, run the program, and inspect variables.
(gdb) break main
(gdb) run <arguments>
Refer to the GDB Documentation for comprehensive usage instructions.
On macOS, use lldb:
(lldb) breakpoint set --name main
(lldb) process launch -- <arguments>
Refer to the LLDB Tutorial for comprehensive usage instructions.