syscall.c

   1 #include "types.h"
   2 #include "defs.h"
   3 #include "param.h"
   4 #include "mmu.h"
   5 #include "proc.h"
   6 #include "x86.h"
   7 #include "syscall.h"
   8
   9 // User code makes a system call with INT T_SYSCALL.
  10 // System call number in %eax.
  11 // Arguments on the stack, from the user call to the C
  12 // library system call function. The saved user %esp points
  13 // to a saved program counter, and then the first argument.
  14
  15 // Fetch the int at addr from process p.
  16 int
  17 fetchint(struct proc *p, uint addr, int *ip)
  18 {
  19   if(addr >= p->sz || addr+4 > p->sz)
  20     return -1;
  21   *ip = *(int*)(addr);
  22   return 0;
  23 }
  24
  25 // Fetch the nul-terminated string at addr from process p.
  26 // Doesn't actually copy the string - just sets *pp to point at it.
  27 // Returns length of string, not including nul.
  28 int
  29 fetchstr(struct proc *p, uint addr, char **pp)
  30 {
  31   char *s, *ep;
  32
  33   if(addr >= p->sz)
  34     return -1;
  35   *pp = (char*)addr;
  36   ep = (char*)p->sz;
  37   for(s = *pp; s < ep; s++)
  38     if(*s == 0)
  39       return s - *pp;
  40   return -1;
  41 }
  42
  43 // Fetch the nth 32-bit system call argument.
  44 int
  45 argint(int n, int *ip)
  46 {
  47   return fetchint(proc, proc->tf->esp + 4 + 4*n, ip);
  48 }
  49
  50 // Fetch the nth word-sized system call argument as a pointer
  51 // to a block of memory of size n bytes.  Check that the pointer
  52 // lies within the process address space.
  53 int
  54 argptr(int n, char **pp, int size)
  55 {
  56   int i;
  57
  58   if(argint(n, &i) < 0)
  59     return -1;
  60   if((uint)i >= proc->sz || (uint)i+size > proc->sz)
  61     return -1;
  62   *pp = (char*)i;
  63   return 0;
  64 }
  65
  66 // Fetch the nth word-sized system call argument as a string pointer.
  67 // Check that the pointer is valid and the string is nul-terminated.
  68 // (There is no shared writable memory, so the string can't change
  69 // between this check and being used by the kernel.)
  70 int
  71 argstr(int n, char **pp)
  72 {
  73   int addr;
  74   if(argint(n, &addr) < 0)
  75     return -1;
  76   return fetchstr(proc, addr, pp);
  77 }
  78
  79 extern int sys_chdir(void);
  80 extern int sys_close(void);
  81 extern int sys_dup(void);
  82 extern int sys_exec(void);
  83 extern int sys_exit(void);
  84 extern int sys_fork(void);
  85 extern int sys_fstat(void);
  86 extern int sys_getpid(void);
  87 extern int sys_kill(void);
  88 extern int sys_link(void);
  89 extern int sys_mkdir(void);
  90 extern int sys_mknod(void);
  91 extern int sys_open(void);
  92 extern int sys_pipe(void);
  93 extern int sys_read(void);
  94 extern int sys_sbrk(void);
  95 extern int sys_sleep(void);
  96 extern int sys_unlink(void);
  97 extern int sys_wait(void);
  98 extern int sys_write(void);
  99 extern int sys_uptime(void);
 100
 101 static int (*syscalls[])(void) = {
 102 [SYS_chdir]   sys_chdir,
 103 [SYS_close]   sys_close,
 104 [SYS_dup]     sys_dup,
 105 [SYS_exec]    sys_exec,
 106 [SYS_exit]    sys_exit,
 107 [SYS_fork]    sys_fork,
 108 [SYS_fstat]   sys_fstat,
 109 [SYS_getpid]  sys_getpid,
 110 [SYS_kill]    sys_kill,
 111 [SYS_link]    sys_link,
 112 [SYS_mkdir]   sys_mkdir,
 113 [SYS_mknod]   sys_mknod,
 114 [SYS_open]    sys_open,
 115 [SYS_pipe]    sys_pipe,
 116 [SYS_read]    sys_read,
 117 [SYS_sbrk]    sys_sbrk,
 118 [SYS_sleep]   sys_sleep,
 119 [SYS_unlink]  sys_unlink,
 120 [SYS_wait]    sys_wait,
 121 [SYS_write]   sys_write,
 122 [SYS_uptime]  sys_uptime,
 123 };
 124
 125 void
 126 syscall(void)
 127 {
 128   int num;
 129
 130   num = proc->tf->eax;
 131   if(num >= 0 && num < NELEM(syscalls) && syscalls[num])
 132     proc->tf->eax = syscalls[num]();
 133   else {
 134     cprintf("%d %s: unknown sys call %d\n",
 135             proc->pid, proc->name, num);
 136     proc->tf->eax = -1;
 137   }
 138 }