Age Owner 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
379 tgl 64 CBC 534932 : relptr_store_eval(char *base, char *val)
65 : {
66 534932 : if (val == NULL)
67 509183 : return 0;
68 : else
69 : {
286 tmunro 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 */
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