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7201cd1862
Previously, we encoded both NULL and the first byte at the base address as 0. That confusion led to the assertion in commite07d4ddc, which failed when min_dynamic_shared_memory was used. Give them distinct encodings, by switching to 1-based offsets for non-NULL pointers. Also improve macro hygiene in passing (missing/misplaced parentheses), and remove open-coded access to the raw offset value from freepage.c/h. Althoughe07d4ddcwas back-patched to 10, the only code that actually makes use of relptr at the base address arrived in84b1c63a, so no need to back-patch further than 14 for now. Reported-by: Justin Pryzby <pryzby@telsasoft.com> Reviewed-by: Robert Haas <robertmhaas@gmail.com> Discussion: https://postgr.es/m/20220519193839.GT19626%40telsasoft.com
94 lines
2.9 KiB
C
94 lines
2.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* relptr.h
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* This file contains basic declarations for relative pointers.
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*
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* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/relptr.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef RELPTR_H
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#define RELPTR_H
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/*
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* Relative pointers are intended to be used when storing an address that may
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* be relative either to the base of the process's address space or some
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* dynamic shared memory segment mapped therein.
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*
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* The idea here is that you declare a relative pointer as relptr(type)
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* and then use relptr_access to dereference it and relptr_store to change
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* it. The use of a union here is a hack, because what's stored in the
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* relptr is always a Size, never an actual pointer. But including a pointer
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* in the union allows us to use stupid macro tricks to provide some measure
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* of type-safety.
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*/
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#define relptr(type) union { type *relptr_type; Size relptr_off; }
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/*
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* pgindent gets confused by declarations that use "relptr(type)" directly,
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* so preferred style is to write
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* typedef struct ... SomeStruct;
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* relptr_declare(SomeStruct, RelptrSomeStruct);
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* and then declare pointer variables as "RelptrSomeStruct someptr".
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*/
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#define relptr_declare(type, relptrtype) \
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typedef relptr(type) relptrtype
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#ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
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#define relptr_access(base, rp) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(__typeof__((rp).relptr_type)) ((rp).relptr_off == 0 ? NULL : \
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(base) + (rp).relptr_off - 1))
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#else
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/*
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* If we don't have __builtin_types_compatible_p, assume we might not have
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* __typeof__ either.
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*/
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#define relptr_access(base, rp) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(void *) ((rp).relptr_off == 0 ? NULL : (base) + (rp).relptr_off - 1))
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#endif
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#define relptr_is_null(rp) \
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((rp).relptr_off == 0)
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#define relptr_offset(rp) \
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((rp).relptr_off - 1)
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/* We use this inline to avoid double eval of "val" in relptr_store */
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static inline Size
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relptr_store_eval(char *base, char *val)
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{
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if (val == NULL)
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return 0;
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else
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{
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Assert(val >= base);
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return val - base + 1;
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}
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}
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#ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
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#define relptr_store(base, rp, val) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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AssertVariableIsOfTypeMacro(val, __typeof__((rp).relptr_type)), \
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(rp).relptr_off = relptr_store_eval((base), (char *) (val)))
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#else
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/*
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* If we don't have __builtin_types_compatible_p, assume we might not have
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* __typeof__ either.
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*/
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#define relptr_store(base, rp, val) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(rp).relptr_off = relptr_store_eval((base), (char *) (val)))
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#endif
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#define relptr_copy(rp1, rp2) \
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((rp1).relptr_off = (rp2).relptr_off)
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#endif /* RELPTR_H */
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