From 2a600a93c7be5b0bf8cacb1af78009db12bc4857 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 13 Aug 2025 16:35:06 -0400 Subject: Make type Datum be 8 bytes wide everywhere. This patch makes sizeof(Datum) be 8 on all platforms including 32-bit ones. The objective is to allow USE_FLOAT8_BYVAL to be true everywhere, and in consequence to remove a lot of code that is specific to pass-by-reference handling of float8, int8, etc. The code for abbreviated sort keys can be simplified similarly. In this way we can reduce the maintenance effort involved in supporting 32-bit platforms, without going so far as to actually desupport them. Since Datum is strictly an in-memory concept, this has no impact on on-disk storage, though an initdb or pg_upgrade will be needed to fix affected catalog entries. We have required platforms to support [u]int64 for ages, so this breaks no supported platform. We can expect that this change will make 32-bit builds a bit slower and more memory-hungry, although being able to use pass-by-value handling of 8-byte types may buy back some of that. But we stopped optimizing for 32-bit cases a long time ago, and this seems like just another step on that path. This initial patch simply forces the correct type definition and USE_FLOAT8_BYVAL setting, and cleans up a couple of minor compiler complaints that ensued. This is sufficient for testing purposes. In the wake of a bunch of Datum-conversion cleanups by Peter Eisentraut, this now compiles cleanly with gcc on a 32-bit platform. (I'd only tested the previous version with clang, which it turns out is less picky than gcc about width-changing coercions.) There is a good deal of now-dead code that I'll remove in separate follow-up patches. A catversion bump is required because this affects initial catalog contents (on 32-bit machines) in two ways: pg_type.typbyval changes for some built-in types, and Const nodes in stored views/rules will now have 8 bytes not 4 for pass-by-value types. Author: Tom Lane Reviewed-by: Peter Eisentraut Discussion: https://postgr.es/m/1749799.1752797397@sss.pgh.pa.us --- src/include/postgres.h | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) (limited to 'src/include/postgres.h') diff --git a/src/include/postgres.h b/src/include/postgres.h index 8a41a668687..e81829bfa6f 100644 --- a/src/include/postgres.h +++ b/src/include/postgres.h @@ -58,15 +58,22 @@ /* * A Datum contains either a value of a pass-by-value type or a pointer to a - * value of a pass-by-reference type. Therefore, we require: - * - * sizeof(Datum) == sizeof(void *) == 4 or 8 + * value of a pass-by-reference type. Therefore, we must have + * sizeof(Datum) >= sizeof(void *). No current or foreseeable Postgres + * platform has pointers wider than 8 bytes, and standardizing on Datum being + * exactly 8 bytes has advantages in reducing cross-platform differences. * * The functions below and the analogous functions for other types should be used to * convert between a Datum and the appropriate C type. */ -typedef uintptr_t Datum; +typedef uint64_t Datum; + +/* + * This symbol is now vestigial, but we continue to define it so as not to + * unnecessarily break extension code. + */ +#define SIZEOF_DATUM 8 /* * A NullableDatum is used in places where both a Datum and its nullness needs @@ -83,8 +90,6 @@ typedef struct NullableDatum /* due to alignment padding this could be used for flags for free */ } NullableDatum; -#define SIZEOF_DATUM SIZEOF_VOID_P - /* * DatumGetBool * Returns boolean value of a datum. @@ -316,7 +321,7 @@ CommandIdGetDatum(CommandId X) static inline Pointer DatumGetPointer(Datum X) { - return (Pointer) X; + return (Pointer) (uintptr_t) X; } /* @@ -326,7 +331,7 @@ DatumGetPointer(Datum X) static inline Datum PointerGetDatum(const void *X) { - return (Datum) X; + return (Datum) (uintptr_t) X; } /* -- cgit v1.2.3