TLA  Line data    Source code

       1                 : /*-------------------------------------------------------------------------
       2                 :  *
       3                 :  * relptr.h
       4                 :  *    This file contains basic declarations for relative pointers.
       5                 :  *
       6                 :  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
       7                 :  * Portions Copyright (c) 1994, Regents of the University of California
       8                 :  *
       9                 :  * src/include/utils/relptr.h
      10                 :  *
      11                 :  *-------------------------------------------------------------------------
      12                 :  */
      13                 : 
      14                 : #ifndef RELPTR_H
      15                 : #define RELPTR_H
      16                 : 
      17                 : /*
      18                 :  * Relative pointers are intended to be used when storing an address that may
      19                 :  * be relative either to the base of the process's address space or some
      20                 :  * dynamic shared memory segment mapped therein.
      21                 :  *
      22                 :  * The idea here is that you declare a relative pointer as relptr(type)
      23                 :  * and then use relptr_access to dereference it and relptr_store to change
      24                 :  * it.  The use of a union here is a hack, because what's stored in the
      25                 :  * relptr is always a Size, never an actual pointer.  But including a pointer
      26                 :  * in the union allows us to use stupid macro tricks to provide some measure
      27                 :  * of type-safety.
      28                 :  */
      29                 : #define relptr(type)     union { type *relptr_type; Size relptr_off; }
      30                 : 
      31                 : /*
      32                 :  * pgindent gets confused by declarations that use "relptr(type)" directly,
      33                 :  * so preferred style is to write
      34                 :  *      typedef struct ... SomeStruct;
      35                 :  *      relptr_declare(SomeStruct, RelptrSomeStruct);
      36                 :  * and then declare pointer variables as "RelptrSomeStruct someptr".
      37                 :  */
      38                 : #define relptr_declare(type, relptrtype) \
      39                 :     typedef relptr(type) relptrtype
      40                 : 
      41                 : #ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
      42                 : #define relptr_access(base, rp) \
      43                 :     (AssertVariableIsOfTypeMacro(base, char *), \
      44                 :      (__typeof__((rp).relptr_type)) ((rp).relptr_off == 0 ? NULL : \
      45                 :         (base) + (rp).relptr_off - 1))
      46                 : #else
      47                 : /*
      48                 :  * If we don't have __builtin_types_compatible_p, assume we might not have
      49                 :  * __typeof__ either.
      50                 :  */
      51                 : #define relptr_access(base, rp) \
      52                 :     (AssertVariableIsOfTypeMacro(base, char *), \
      53                 :      (void *) ((rp).relptr_off == 0 ? NULL : (base) + (rp).relptr_off - 1))
      54                 : #endif
      55                 : 
      56                 : #define relptr_is_null(rp) \
      57                 :     ((rp).relptr_off == 0)
      58                 : 
      59                 : #define relptr_offset(rp) \
      60                 :     ((rp).relptr_off - 1)
      61                 : 
      62                 : /* We use this inline to avoid double eval of "val" in relptr_store */
      63                 : static inline Size
      64 CBC      534932 : relptr_store_eval(char *base, char *val)
      65                 : {
      66          534932 :     if (val == NULL)
      67          509183 :         return 0;
      68                 :     else
      69                 :     {
      70           25749 :         Assert(val >= base);
      71           25749 :         return val - base + 1;
      72                 :     }
      73                 : }
      74                 : 
      75                 : #ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
      76                 : #define relptr_store(base, rp, val) \
      77                 :     (AssertVariableIsOfTypeMacro(base, char *), \
      78                 :      AssertVariableIsOfTypeMacro(val, __typeof__((rp).relptr_type)), \
      79                 :      (rp).relptr_off = relptr_store_eval((base), (char *) (val)))
      80                 : #else
      81                 : /*
      82                 :  * If we don't have __builtin_types_compatible_p, assume we might not have
      83                 :  * __typeof__ either.
      84                 :  */
      85                 : #define relptr_store(base, rp, val) \
      86                 :     (AssertVariableIsOfTypeMacro(base, char *), \
      87                 :      (rp).relptr_off = relptr_store_eval((base), (char *) (val)))
      88                 : #endif
      89                 : 
      90                 : #define relptr_copy(rp1, rp2) \
      91                 :     ((rp1).relptr_off = (rp2).relptr_off)
      92                 : 
      93                 : #endif                          /* RELPTR_H */