从内存中逐字节读取数据，而无需系统调用或C语言中的库函数

Question

I want to move information byte by byte from one memory location to another without using any library function. Am using a 16bits architecture emulated in qemu and this code is part of tiny small kernel i am writing, so i can not use any system call

// The struct i want to copy
struct procinfo info_tmp;
// here i put some stuff in my struct    
info_tmp.pid = tablaprocesos[indiceProceso].pid;
kstrcpy(info_tmp.nombre, tablaprocesos[indiceProceso].nombre);  
info_tmp.segmento = tablaprocesos[indiceProceso].memoria;
if(tablaprocesos[indiceProceso].estado==PROCESO_LISTO)
  info_tmp.estado = 0;
else if(tablaprocesos[indiceProceso].estado==PROCESO_RUN)
  info_tmp.estado = 1;
else if(tablaprocesos[indiceProceso].estado==BLOQ_TECLADO ||
tablaprocesos[indiceProceso].estado==PROCESO_SYSCALL)
  info_tmp.estado = 2;
else
  info_tmp.estado = 3; // Zombie
// Tiempo total = tiempoSYS + tiempoUSER
info_tmp.tiempo = tablaprocesos[indiceProceso].tiempoUSER +
  tablaprocesos[indiceProceso].tiempoSYS;    

// pointer to destination that i want to copy to
infoProc = (struct procinfo *)(((int)es << 16) + (0x0000ffff & ebx));
// now pointer to my source struct  
procinfo * origen = &info_tmp;         
int limit = sizeof(struct procinfo);
int i;
for(i=0;i<limit;i++){  
   //  I need here to read only one byte from my source pointer to a variable "byte"

   // macro written in ASM to copy one byte to a pointed location
   // it writes in another data segment of another process
   WRITE_POINTER_FAR(infoProc,byte);
   // next byte
   origen += 1; 
   infoProc += 1;
}

Is there a direct way to do it without the need to write a small code in ASM to do it manually ?

Note: This code is part of a 16bits segmented OS kernel (a 64KB segment for each process), the source struct is in the kernel segment and i want to copy it to a location in another process segment and it can not be like *targetBytePointer = *sourceBytePointer.

Answer 1

// The struct i want to copy
struct procinfo info_tmp;
// here i put some stuff in my struct    
info_tmp.pid = tablaprocesos[indiceProceso].pid;
kstrcpy(info_tmp.nombre, tablaprocesos[indiceProceso].nombre);  
info_tmp.segmento = tablaprocesos[indiceProceso].memoria;

switch(tablaprocesos[indiceProceso].estado) {
case PROCESO_LISTO:
  info_tmp.estado = 0; break;
case PROCESO_RUN:
  info_tmp.estado = 1; break;
case BLOQ_TECLADO :
case PROCESO_SYSCALL:
  info_tmp.estado = 2; break;
default:
  info_tmp.estado = 3; // Zombie
        break;
        }
// Tiempo total = tiempoSYS + tiempoUSER
info_tmp.tiempo = tablaprocesos[indiceProceso].tiempoUSER +
  tablaprocesos[indiceProceso].tiempoSYS;

// pointer to destination that i want to copy to
infoProc = (struct procinfo *)(((int)es << 16) + (0x0000ffff & ebx));
char *dest = (char*) infoProc;
// now pointer to my source struct  
char * origen = (char*) &info_tmp;
int limit = sizeof(struct procinfo);
int i;
for(i=0;i<limit;i++){ 
   char byte;
   //  I need here to read only one byte from my source pointer to a variable "byte"

   // macro written in ASM to copy one byte to a pointed location
   // it writes in another data segment of another process
   byte = *origen;
   WRITE_POINTER_FAR(dest,byte);
   // next byte
   origen += 1;
   dest += 1;
}

Answer 2

I finally wrote a small ASM code to do it manually. I had to, because as i noted before it is a fragment of code of a 16bits kernel i am writing and emulating in qemu and that does memory segmentation (64KB for each process and 10 processes total). I can not do *targetBytePointer = *sourceBytePointer as targetPointer is in the process segment and sourcePointer is in the kernel segment and that is why i have the macro WRITE_POINTER_FAR for. Basically WRITE_POINTER_FAR (written is ASM) will use the destination pointer that i already created combining what the calling process passed to me in two registers (ES:BX), and will write only one byte to that destination and that's why i needed to read only one byte from my source each time.

char byte;
struct procinfo * origen = &info_tmp;  
for(i=0;i<limit;i++){
  asm( // leer un byte
    "mov %1,%%ebx   \n\t"
    "mov (%%ebx),%0  \n\t"
    :"=r"(byte)
    :"r"(origen)
  );
  WRITE_POINTER_FAR(infoProc,byte);
  origen += 1;
  infoProc += 1;
}

Edit: another simple solution

char *byte;
struct procinfo * origen = &info_tmp;  
for(i=0;i<limit;i++){     
  byte = (char*)origen;
  WRITE_POINTER_FAR(infoProc,*byte);
  origen += 1;
  infoProc += 1;
}
// actualizar puntero de proceso
if(indiceProceso+1<=MAX_PROCESOS)
  indiceProceso++;
return 0;