lots-o-dwarf

This script is intended to test the impact of having lots of split dwarf files on debugger startup time. It will generate a large number of object files, each with a single function. It combines these object files into libraries and links it all together into an executable. For each of the object file a separate debug info file (.dwo) is generated by the compiler.

It then times the the startup time of launching a debugger to load the executable.

The --count option is the scaling parameter for the script. This defines how many "leaf" functions are generated. These leaf functions are compiled separately into object files with split dwarf (.dwo). They are then combined into libraries (determined by --library-object-count) and linked into a main executable.

The script generates all outputs into a directory chosen by the --output-directory flag. The default location is a build directory next to the script. This directory contains all generated source files, a ninja build file and the compiled object and dwo files.

Usage

The script includes builtin help for all supported options. Basic usage will be to point it to your compiler and debugger executables and select which debuggers should be run (gdb, lldb, or both).

Use the --count flag described above to control the number of generated leaf functions. The count parameter will not be exactly equal to the number of generated files since it controls the number of leaf functions. Additional files will be generated for libraries and the main executable.

After initially generating and building the files you can re-run the timings without re-generating anything by using the --skip-generate flag.

$ ./lod.py --clang=clang++ --gdb=gdb --lldb=lldb --build --run both --stats
...
time -v gdb build/bin/lod -ex quit
...
time -v lldb /home/peix/work/lots-o-dwarf/build/bin/lod -o quit
...
===================== Stats =====================
Executable size:   1.1MiB count: 1
ObjectFile size:   3.8MiB count: 12
Library    size:   4.2MiB count: 1
DebugInfo  size:   2.7MiB count: 12

Requirements

• c++ compiler (clang++ or g++)
• ninja
• debugger (gdb or lldb)