Shared

Important

As explained in Loading a simulation, in order to load binaries/libraries dynamically, those need to be built as position independent code/executables (PIC/PIE).

shlib

This example features the same functionality as random. However, custom C sources are use (as in customc) and these are built as a shared library. See Loading foreign objects from within a simulation for further info.

dlopen

Although this example does not include a simulation built with GHDL, it is a test and the introduction to the next example. In this test, two separate shared libraries are built from C sources, both including a function named ghdl_main. Then, in a main C application, both shared libraries are dynamically loaded at the same time, and both are executed (one after the other)

This example tests whether symbol ghdl_main is visible in the shared libraries, and whether the same symbol name can be loaded from multiple shared libraries (and used) at the same time.

Tip

If the symbol is not found, try adding -g, -rdynamic and/or -O0 when building the shared libraries. Tools such as objdump, readelf or nm can be used to check if a symbol is visible. For instance, objdump -d corea.so | grep ghdl_main.

Hint

Building multiple designs as separate artifacts and dynamically loading them at the same time is a naive approach to multi-core simulation with GHDL. It is also a possible solution for coarse grained co-simulation with Verilator.

shghdl

This example is complementary to shlib, since the VHDL simulation is built as a shared library, which is then loaded from a main C application (as in dlopen).

When main is executed:

• The shared libray is loaded, symbol print_something is searched for, and it is executed.
• Symbol ghdl_main is searched for, and it is executed three times. Unfortunately, GHDL does not currently support reseting/restarting the simulation runtime. Hence, in this example the shared library is unloaded and loaded again before calling ghdl_main after the first time.

See Generating_shared_libraries for further details with regard to the visibility of symbols in the shared libraries.

Note

On GNU/linux, both executable binaries and shared libraries use the ELF format. As a result, although hackish, it is possible to load an executable binary dynamically, i.e. without using any of the shared options explained in Generating_shared_libraries. In this example, this case is also tested. However, this is not suggested at all, since it won’t work on all platforms.