Goal

TVM makes frequent use of packed functions, which may be implemented in any language supported by the FFI. This can cause stack traces to be difficult to read, as there may be several stack frames devoted to the FFI or to CPython calls that do not represent the issue being debugged. This gdb extension exists to hide those stack frames, allowing the actual flow of the program to be more easily traced.

Usage

• Install debug symbols for python. (e.g. sudo apt install pythonX.Y-dbg)
• Source this file in your .gdbinit source ~/path/to/the/tvm-gdb-extension/source-me.py

Known Configuration Issues

• Why are Python/PackedFunc frames still displayed, but indented?

  gdb indents elided frames by default, but still displays them. With gdb 9.1 or higher, elided frames can be hidden using bt -hide. For earlier versions of gdb, or to hide the elided frames by default, set the environment variable TVM_GDB_HIDE_ELIDED_FRAMES to a non-zero integer.

• Why are python stack frames not being displayed?

  Python must have debug symbols available in order to identify python calls, either embedded in the file or as a separate debug file.

  • To check if debug symbols are available in the python executable, run objdump --syms $(which python3) | grep .debug_info If no results are printed, debug symbols are missing from the executable.

  • To check if debug symbols are available in a separate file, first find the name of the debug file using readelf --string-dump .gnu_debuglink $(which python3). Then, find the gdb debug dir using gdb --config. Finally, check if the file exists in the gdb debug-dir. These steps can be done with the following bash command.

    find "$(gdb --config | grep with-separate-debug-dir | \
            sed 's/\s\+--with-separate-debug-dir=//g; s/\s\+(relocatable)//g;')" \
        -name $(readelf --string-dump .gnu_debuglink $(which python3) | \
                grep -o "[0-9a-f]\+.debug")

    If no results are printed, the separate debug file is not automatically loaded.

  • If your version of gdb is not the system version of gdb, you may need to recompile with ./configure --with-separate-debug-dir=/usr/lib/debug

• Why are python stack frames displayed as Unknown python function () at Unknown python file?

  The gdb extensions provided by python (e.g. python3.8-gdb.py) must be locatable by gdb. These are typically stored in /usr/share/gdb/auto-load.

  If your version of gdb is not the system version of gdb, you may need to recompile with ./configure --with-auto-load=/usr/share/gdb/auto-load