src/harness_adapter.c


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// This file provides functions for the wetterhorn harness that are not
// expressible directly in haskell.
//
// Currently these functions exclusively enable/disable the Haskell runtime.

#include "HsFFI.h"
#include "plugin_interface.h"
#include <stdio.h>

const char *plugin_name = "Wetterhorn";

void plugin_load(int argc, char **argv) { hs_init(&argc, &argv); }
void plugin_teardown(opqst_t st) { hs_exit(); }

static const char msg[] =
    "Wetterhorn Plugin v 0.01\n\n"
    "Welcome, and thank you for your interest.\n\n"
    "This is merely a plugin to the Wetterhorn Compositor and not meant to be\n"
    "executed as a standalone binary. This plugin requires a harness to run\n"
    "To use this file, please use './wtr_harness [full-path-to-wtr.so]'\n"
    "That will allow you to see how this compositor works in all its glory!\n";
static const int msg_sz = sizeof(msg);


__attribute__((naked)) void _start() {

  // Make system call to print the message
  asm(
      // Load the address of the string into rsi
      "mov %0, %%rsi\n"
      // Load the string length into edx
      "mov %1, %%edx\n"
      // Load the file descriptor for stdout into edi
      "mov $1, %%edi\n"
      // Load the syscall number for sys_write into eax
      "mov $1, %%eax\n"
      // Make the syscall
      "syscall\n"

      // Exit the program.
      "mov $0, %%rdi\n"
      "mov $60, %%rax\n"
      "syscall\n"
      :
      : "r"(msg), "r"(msg_sz)  // Input: address of msg
      : "%rsi", "%edx", "%edi" // Clobbered registers
  );
}