# Environment

This section describes the environment variables used by Verilator and associated programs.

LD_LIBRARY_PATH

  A generic Linux/OS variable specifying what directories have shared object (.so) files. This path should include SystemC and other shared objects needed at simulation runtime.

MAKE

  Names the executable of the make command invoked when using the `--build` option. Some operating systems may require “gmake” to this variable to launch GNU make. If this variable is not specified, “make” is used.

MAKEFLAGS

  Flags created by make to pass to submakes. Verilator searches this variable to determine if a jobserver is used; see `--build-jobs`.

OBJCACHE

  Optionally specifies a caching or distribution program to place in front of all runs of the C++ compiler. For example, “ccache” or “sccache”. If using distcc or icecc/icecream, they would generally be run under ccache; see the documentation for those programs. If OBJCACHE is not set, and at configure time ccache was present, ccache will be used as a default.

SYSTEMC

  Deprecated. Used only if `SYSTEMC_INCLUDE` or `SYSTEMC_LIBDIR` is not set. If set, specifies the directory containing the SystemC distribution. If not specified, it will come from a default optionally specified at configure time (before Verilator was compiled).

SYSTEMC_ARCH

  Deprecated. Used only if `SYSTEMC_LIBDIR` is not set. Specifies the architecture name used by the SystemC kit. This is the part after the dash in the “lib-{…}” directory name created by a make in the SystemC distribution. If not set, Verilator will try to intuit the proper setting, or use the default optionally specified at configure time (before Verilator was compiled).

SYSTEMC_CXX_FLAGS

  Specifies additional flags that are required to be passed to GCC when building the SystemC model. System 2.3.0 may need this set to “-pthread”.

SYSTEMC_INCLUDE

  If set, specifies the directory containing the systemc.h header file. If not specified, it will come from a default optionally specified at configure time (before Verilator was compiled), or computed from SYSTEMC/include.

SYSTEMC_LIBDIR

  If set, specifies the directory containing the libsystemc.a library. If not specified, it will come from a default optionally specified at configure time (before Verilator was compiled), or computed from SYSTEMC/lib-SYSTEMC_ARCH.

VERILATOR_BIN

  If set, specifies an alternative name of the `verilator` binary. May be used for debugging and selecting between multiple operating system builds.

VERILATOR_COVERAGE_BIN

  If set, specifies an alternative name of the `verilator_coverage` binary. May be used for debugging and selecting between multiple operating system builds.

VERILATOR_GDB

  If set, the command to run when using the `--gdb` option, such as “ddd”. If not specified, it will use “gdb”.

VERILATOR_ROOT

  The `VERILATOR_ROOT` environment variable is used in several places:

  - At `./configure` time: If set, it is embedded into the binary, and at runtime if `VERILATOR_ROOT` is not set, the embedded value is used for the runtime default.

  - When `verilator` is run: If `VERILATOR_ROOT` is set it will be used to find the `verilator_bin` executable (this is the actual Verilator binary; `verilator` is a Perl wrapper). If not set, the `verilator` script uses other methods to find `verilator_bin` (looking in the same directory and falling back to `$PATH`).

  - When `make` is run on the Makefile generated by `verilator`: The value of `VERILATOR_ROOT` (falling back to the value embedded in the binary if not set) is used to find the include files (`include/verilated.mk`).

  If you are using a pre-compiled Verilator package, you should not need to set `VERILATOR_ROOT` - the value embedded in the binary should be correct. In fact this option does not work with Verilator packages that have been installed with `make install`. If a Verilator package has been installed using `./configure --prefix=/some/path && make install` and then moved to another location, you cannot use `VERILATOR_ROOT` to point to the new version.

  See Installation for more details.

# Make Variables

This section describes the make variables used by Verilator. These may be set by passing them to make e.g. `make CXX=my-gcc ...`.

AR

  Optionally overrides the default ar (archive) binary used by the Verilated makefiles. If AR is not set, the version found at configure time is used.

CXX

  Optionally overrides the default compiler binary used by the Verilated makefiles. If CXX is not set, the version found at configure time is used. Note the default flags passed to the compiler are determined at configuration time, so changing the CXX compiler version using this variable, as opposed to passing it at configuration time, may not give desired results.

LINK

  Optionally overrides the default linker binary used by the Verilated makefiles. If LINK is not set, the version found at configure time is used. Note the default flags passed to the linker are determined at configuration time, so changing the LINK version using this variable, as opposed to passing it at configuration time, may not give desired results.

PERL

  Optionally overrides the default perl binary used by the Verilated makefiles. If PERL is not set, the version found at configure time, and compiled into the Verilator binary, is used.

PYTHON3

  Optionally overrides the default python3 binary used by the Verilated makefiles. If PYTHON3 is not set, the version found at configure time is used.