DPI-C and SystemVerilog External Compilation flow issue - gcc

Question

ModelSim User's manual (v10.1c), in page 660, talks about the default autocompile flow (using vlog) and external compilation flow to get the the DPI-C to work in ModelSim. I'm able to get the auto-compile flow to work. I'm stuck with the external compilation flow.
Problem Summary: I get an "undefined reference" error in when I try to create the .dll file in-spite of using the right export and import statements in my system verilog file.
Here are the files that make up this project:
file 1: mytest.cpp
#include<stdio.h>
#include "experiment3.h"
int mymain() {
printf("---starting test in c-domain---\n");
PrintHelloWorld();
return 0;
}
file 2: experiment3.h
#ifndef INCLUDED_EXPERIMENT3
#define INCLUDED_EXPERIMENT3
#ifdef __cplusplus
#define DPI_LINK_DECL extern "C"
#else
#define DPI_LINK_DECL
#endif
#include "svdpi.h"
DPI_LINK_DECL DPI_DLLESPEC
int
mymain();
DPI_LINK_DECL void
PrintHelloWorld();
#endif
file 3: mytb.sv
module mytb;
timeunit 1ns/1ps;
export "DPI-C" function PrintHelloWorld;
import "DPI-C" context task mymain();
function void PrintHelloWorld();
$display("HelloWorld\n");
endfunction
//start test
initial begin
#10ns;
mymain();
end
endmodule
Here are the command that I am using:
command 1 :g++ -c -IC:\intelFPGA\17.0\modelsim_ase\include -o ./mytest.o ./mytest.cpp
comments :command 1 executes without any problem
key-words :MinGW, GCC
command 2 :g++ -shared -Bsymbolic -o ./mytest.dll ./mytest.o -LC:\intelFPGA\17.0\modelsim_ase\win32aloem
comments :[1] command 2 fails when I use the mytest.cpp showed above
[2] command 2 passes when I comment out "PrintHelloWorld()" in mytest.cpp
error :c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe:
./mytest.o:mytest.cpp:(.text+0x2d): undefined
reference to '`PrintHelloWorld' collect2.exe:error:ld
returned 1 exit status
key-words :MinGW, GCC, dll
command 3 : vsim -sv_lib ../src_cpp/mytest work.mytb
comments : [1] executed in console in ModelSim
[2] works when I don't have "PrintHelloWorld()" in mytest.cpp
Most of the online DPI-C examples deal with running (CPP and .SV) everything in ModelSim. I don't want that. I want to keep the HW and SW flow separate. And, this separation does work to some extent (I have no issues with calling C functions from SV (import works fine). The roadblock is with trying to call SystemVerilog function from the C function (something seems to be wrong with the export).
Any thoughts on how I can get past this hurdle ?

Answer 1

Based on looking at examples, try adding -fPIC to your command 1. Then command 2 should work as is.
From my experience the final file should be a shared object (.so); not a dynamic link library (.dll). I run SystemVerilog on unix based systems, so maybe windows is different. If you run into an issue, that could be something to try.

Answer 2

Try changing
DPI_LINK_DECL void
PrintHelloWorld();
to
DPI_LINK_DECL DPI_DLLISPEC void
PrintHelloWorld();
(if DPI_DLLISPEC doesn't work replace it directly with __declspec(dllimport))