Change file to support extensions to NNIX in the simple MMIX simulator
(This change file is public domain)

@x
The |TRAP| instruction is not simulated, except for the system calls
mentioned in the introduction.
@y
The |TRAP| instruction is not simulated, except for the system calls
mentioned in the introduction, and extensions to the system calls that
can be loaded from external files.
@z

@x
case TRAP:@+if (xx!=0 || yy>max_sys_call) goto privileged_inst;
@y
case TRAP:
if(xx) @<Execute an operating system extension@>@;
if(yy>max_sys_call) goto privileged_inst;
@z

@x
#include <signal.h>
@y
#include <signal.h>
#include <dlfcn.h>
@z

@x
@* Index.
@y
@* Extensions. This chapter contains the stuff needed for loading
extensions to the operating system interface.

@ @<Type...@>=
typedef int(*extension_func)(octa*g,int yy,int zz,int(*mmgetchars)(char*,int,octa,int),void(*mmputchars)(unsigned char*,int,octa));

@ @<Execute an operating system extension@>= {
  static extension_func ioext[256];
  if(!ioext[xx]) {
    char s[128];
    void*d;
    dlerror();
    sprintf(s,"./mmix-ext%d.so",xx);
    d=dlopen(s,RTLD_NOW|RTLD_LOCAL);
    if(!d) {
      fprintf(stderr,"Extension error: %s\n",dlerror()?:"Unknown error");
      goto privileged_inst;
    }
    ioext[xx]=dlsym(d,"mmix_extension");
    if(!ioext[xx]) {
      fprintf(stderr,"Extension error: %s\n",dlerror()?:"Value of symbol 'mmix_extension' is NULL");
      goto privileged_inst;
    }
  }
  g[rBB]=g[255];
  g[255]=g[rJ];
  g[rWW]=inst_ptr;
  g[rXX].h=sign_bit, g[rXX].l=inst;
  g[rYY]=y, g[rZZ]=z;
  z.h=0, z.l=zz;
  if(ioext[xx](g,yy,zz,mmgetchars,mmputchars)) goto privileged_inst;
  inst_ptr=g[rWW];
  x=g[255]=g[rBB];@+break;
}

@* Index.
@z

Please add the following codes into a file named "mmix-ext.h":

typedef unsigned int tetra;
typedef struct {tetra h,l;} octa;
int mmix_extension(octa*g,int yy,int zz,int(*mmgetchars)(char*,int,octa,int),void(*mmputchars)(unsigned char*,int,octa));
enum{
 rB,rD,rE,rH,rJ,rM,rR,rBB,
 rC,rN,rO,rS,rI,rT,rTT,rK,rQ,rU,rV,rG,rL,
 rA,rF,rP,rW,rX,rY,rZ,rWW,rXX,rYY,rZZ,
};