Simulation and runtime debugging options

Besides the options described in Synthesis command, GHDL passes any debugging options (those that begin with -g) and optimizations options (those that begin with -O or -f) to GCC. Refer to the GCC manual for details. Moreover, some debugging options are also available, but not described here. The --help option lists all options available, including the debugging ones.


Display signals after each cycle.


Display process name before each cycle.


Display run-time statistics.


Display signals order.


Display sources while displaying signals.


Display signal types.


Display map bw declared signals and internal signals.


Display internal signals.


Do internal checks after each process run.


Watch activity of LEVEL signals: LEVEL is all, min (default) or none (unsafe).


Dump Run Time Information (RTI).


Allow --work=std

GNU Debugger (GDB)


Debugging VHDL programs using GDB is possible only with GCC/LLVM.

GDB is a general purpose debugger for programs compiled by GCC. Currently, there is no VHDL support for GDB. It may be difficult to inspect variables or signals in GDB. However, it is still able to display the stack frame in case of error or to set a breakpoint at a specified line.

GDB can be useful to catch a runtime error, such as indexing an array beyond its bounds. All error check subprograms call the __ghdl_fatal procedure. Therefore, to a catch runtime error, set a breakpoint like this:

(gdb) break __ghdl_fatal

When the breakpoint is hit, use the where or bt command to display the stack frames.