iverilog build in Nix standard repos has a bug

[esophagus-now]

(Apologies for duplicate post; I'm not used to github and someone told me to post a discussion instead of a comment)

Original comment from this commit: 580170d

I am using iverilog in repl.it (via Nix). I don't know much about where this distribution of iverilog comes from (or who maintains it) but maybe this is a clue?

$ which iverilog
/nix/store/q0rhxcs2hfri6ja2fas671ywiszk20qr-iverilog-11.0/bin/iverilog

I ran into a segfault with a cbAfterDelay callback, and after single-stepping the asm in the debugger I found a mysterious call to __dynamic_cast that wasn't in the v11_branch. Luckily, clicking on the history for this file turns up this fix, so I'm guessing my installation was made before this fix.

As a workaround I just put a dummy vpiHandle and it fixed the problem. Here is the particular code I am using:

int vpi_wait(lua_State *L) {
    //Annoying... Icarus verilog doesn't support vpiScaledRealTime
    //double delay_time = luaL_checknumber(L, 1);
    lua_Integer delay_time = luaL_checkinteger(L, 1);
    if (delay_time < 0) {
        luaL_error(L, "Cannot wait for %ld; delay must be positive", delay_time);
    }

    s_vpi_time delay;
    //delay.type = vpiScaledRealTime;
    //delay.real = delay_time;
    delay.type = vpiSimTime;
    delay.low = (delay_time) & 0xFFFFFFFF;
    delay.high = (delay_time >> 32) & 0xFFFFFFFF;

    s_cb_data cbdat;
    cbdat.reason = cbAfterDelay;
    cbdat.time = &delay;
    cbdat.cb_rtn = &resume_lua_after_wait;
    cbdat.user_data = (char*)L;

    //The version of iverilog I'm using must have been built
    //before this fix: https://github.com/steveicarus/iverilog/commit/580170d9745a0883b69c8d63d21553d9ad874698
    //I will put some arbitrary valid vpi handle in obj as a workaround
    vpiHandle it = vpi_iterate(vpiModule, NULL);
    vpiHandle el = vpi_scan(it);
    assert(el != NULL);
    if (it != NULL) vpi_free_object(it);

    cbdat.obj = el;
    
    vpi_register_cb(&cbdat);

    cerr << "yeilding..." << endl;
    lua_yieldk(L, 0, 0, &lua_repl);

    puts("should never get here...");
    //Can never get here
    return 0;
}

You can see the whole project here