Call C function from Reaper JSFX PoC

jsfx_addfunc.c

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <math.h>

#include "ns-eel.h"

#ifndef I_KNOW_WHAT_I_AM_DOING
#error Hardcoded offsets are for 32-bit 5.95 and possibly other versions
#endif

#define BASE 0x10000000UL

typedef void (*pNSEEL_addfunc_ret_type_t)(const char *, int, int, NSEEL_PPPROC, void *, eel_function_table *);
static pNSEEL_addfunc_ret_type_t pNSEEL_addfunc_ret_type = (pNSEEL_addfunc_ret_type_t)(0x10002220UL - BASE);
static NSEEL_PPPROC NSEEL_PProc_THIS = (NSEEL_PPPROC)(0x10008b00UL - BASE);
static void NSEEL_addfunc_ret_type(const char *name, int np, int ret_type, NSEEL_PPPROC pproc, void *fptr, eel_function_table *destination) {
	pNSEEL_addfunc_ret_type(name, np, ret_type, pproc, fptr, destination);
}

static EEL_F NSEEL_CGEN_CALL add(void *opaque, EEL_F *a, EEL_F *b) {
	return *a + *b;
}
static int NSEEL_CGEN_CALL setReaEQCircleSize(void *opaque, EEL_F *size) {
	HMODULE reaeq = GetModuleHandle("reaeq.dll");
	if (reaeq == NULL) {
		return 0;
	}
	DWORD textSize = 0x31000;
	DWORD prot;
	if (!VirtualProtect(reaeq+0x1000, textSize, PAGE_EXECUTE_READWRITE, &prot)) {
		return 0;
	}
	*(float *)(0x1001416CUL - BASE + (DWORD)reaeq) = *size;
	char sz = lround(*size) + 1;
	*(char *)(0x10016D04UL - BASE + (DWORD)reaeq) = -sz;
	*(char *)(0x10016D43UL - BASE + (DWORD)reaeq) = sz;
	*(char *)(0x10016DF2UL - BASE + (DWORD)reaeq) = sz;
	*(char *)(0x10016E4FUL - BASE + (DWORD)reaeq) = -sz;
	DWORD t;
	VirtualProtect(reaeq+0x1000, textSize, prot, &t);
	return 1;
}

static DWORD (*JesusonicAPI_init)(DWORD, DWORD, DWORD);

static DWORD init(DWORD arg1, DWORD arg2, DWORD arg3) {
	DWORD ret = JesusonicAPI_init(arg1, arg2, arg3);
	NSEEL_addfunc_retval("myadd", 2, NSEEL_PProc_THIS, add);
	NSEEL_addfunc_retbool("setReaEQCircleSize", 1, NSEEL_PProc_THIS, setReaEQCircleSize);
	return ret;
}

__declspec(dllexport)
int ReaperPluginEntry(HINSTANCE hInstance, void *rec) {
	if (rec == NULL) { return 0; }
	HMODULE jsfx = GetModuleHandle("jsfx.dll");
	if (jsfx == NULL) { return 0; }
	pNSEEL_addfunc_ret_type = (pNSEEL_addfunc_ret_type_t)((DWORD)pNSEEL_addfunc_ret_type + (DWORD)jsfx);
	NSEEL_PProc_THIS = (NSEEL_PPPROC)((DWORD)NSEEL_PProc_THIS + (DWORD)jsfx);
	void **JesusonicAPI = (void **)GetProcAddress(jsfx, "JesusonicAPI");
	if (JesusonicAPI == NULL) { return 0; }
	JesusonicAPI_init = (DWORD (*)(DWORD,DWORD,DWORD))JesusonicAPI[1];
	JesusonicAPI[1] = init;
	return 1;
}

awesome, thanks ess7. one correction, your original code requires the functions from jsfx.dll, not reaper.exe. that may also help them change less frequently (depending on how often they update jsfx.dll).

I managed to get them from Ghidra following your v. helpful instructions. For Reaper 6.4 (x64), they are:

#define BASE 0x180000000
static pNSEEL_addfunc_ret_type_t pNSEEL_addfunc_ret_type = (pNSEEL_addfunc_ret_type_t)(0x18000ceb8 - BASE);
static NSEEL_PPPROC NSEEL_PProc_THIS = (NSEEL_PPPROC)(0x180004338 - BASE);

And as it's 64bit, change JesusonicAPI_init() and pointer math to use LONG_PTR instead of DWORD (or just int):

static LONG_PTR (*JesusonicAPI_init)(LONG_PTR, LONG_PTR, LONG_PTR);

I just remembered I dumped the undocumented functions exported by reaper_plugin_info_t GetFunc() and the NSEEL functions are there:
https://stash.reaper.fm/v/34480/Undocumented%20API%20functions.txt

REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(REAPER_PLUGIN_HINSTANCE hInstance, reaper_plugin_info_t *rec) {
  ...
  pNSEEL_addfunc_ret_type = (pNSEEL_addfunc_ret_type_t)rec->GetFunc("NSEEL_addfunc_ret_type");
  NSEEL_PProc_THIS = (NSEEL_PPPROC)rec->GetFunc("NSEEL_PProc_THIS");
  ...

I'm getting the correct addresses but the function is not registered. Even EEL_string_register is not called by Reaper but the string functions work. Still investigating.

By the way I wanted to reply to the Reaper forum threads about this topic. Tried registering, waited for approval, but they banned my IP.

Added a new gist that works on 6.40 x64:
https://gist.github.com/ess7/6c75c111194a9159d05472aadc956c01

I'll add some commentary later. If it doesn't work try a "Full recompile/reset"