minix/lib/libc/sys/kernel_utils.c

   1 /*
   2  * This file contains the main routine for retrieval of the kernel information
   3  * page, as well as abstraction routines for retrieval of specific values from
   4  * this kernel-mapped user information structure.  These routines may be used
   5  * from both userland and system services, and their accesses are considered to
   6  * establish part of the userland ABI.  Do not add routines here that are not
   7  * for retrieval of userland ABI fields (e.g., clock information)!  Also, since
   8  * these functions are MINIX3 specific, their names should contain - preferably
   9  * be prefixed with - "minix_".
  10  */
  11
  12 #define _MINIX_SYSTEM
  13
  14 #include <sys/cdefs.h>
  15 #include "namespace.h"
  16 #include <lib.h>
  17 #include <minix/param.h>
  18 #include <assert.h>
  19
  20 extern struct minix_kerninfo *_minix_kerninfo;
  21
  22 /*
  23  * Get a pointer to the kernel information page.
  24  */
  25 struct minix_kerninfo *
  26 get_minix_kerninfo(void)
  27 {
  28
  29         assert(_minix_kerninfo != NULL);
  30
  31         return _minix_kerninfo;
  32 }
  33
  34 /*
  35  * Obtain the initial stack pointer for a new userland process.  This value
  36  * is used by routines that set up the stack when executing a new program.
  37  * It is used for userland exec(2) and in various system services.
  38  */
  39 vir_bytes
  40 minix_get_user_sp(void)
  41 {
  42         struct minix_kerninfo *ki;
  43
  44         /* All information is obtained from the kernel information page. */
  45         ki = get_minix_kerninfo();
  46
  47         /*
  48          * Check whether we can retrieve the user stack pointer value from the
  49          * kuserinfo structure.  In general, this test is the correct one to
  50          * see whether the kuserinfo structure has a certain field.
  51          */
  52         if ((ki->ki_flags & MINIX_KIF_USERINFO) &&
  53             KUSERINFO_HAS_FIELD(ki->kuserinfo, kui_user_sp)) {
  54                 return ki->kuserinfo->kui_user_sp;
  55         }
  56
  57         /*
  58          * Otherwise, fall back to legacy support: retrieve the value from the
  59          * kinfo structure.  This field will eventually be removed.
  60          */
  61         return ki->kinfo->user_sp;
  62 }