Get rid of our dependency on type "long" for memory size calculations.

Consistently use "Size" (or size_t, or in some places int64 or double)
as the type for variables holding memory allocation sizes.  In most
places variables' data types were fine already, but we had an ancient
habit of computing bytes from kilobytes-units GUCs with code like
"work_mem * 1024L".  That risks overflow on Win64 where they did not
make "long" as wide as "size_t".  We worked around that by restricting
such GUCs' ranges, so you couldn't set work_mem et al higher than 2GB
on Win64.  This patch removes that restriction, after replacing such
calculations with "work_mem * (Size) 1024" or variants of that.

It should be noted that this patch was constructed by searching
outwards from the GUCs that have MAX_KILOBYTES as upper limit.
So I can't positively guarantee there are no other places doing
memory-size arithmetic in int or long variables.  I do however feel
pretty confident that increasing MAX_KILOBYTES on Win64 is safe now.
Also, nothing in our code should be dealing in multiple-gigabyte
allocations without authorization from a relevant GUC, so it seems
pretty likely that this search caught everything that could be at
risk of overflow.

Author: Vladlen Popolitov <v.popolitov@postgrespro.ru>
Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1a01f0-66ec2d80-3b-68487680@27595217

2 files changed, 8 insertions, 4 deletions

diff --git a/src/include/utils/dsa.h b/src/include/utils/dsa.h
index 44f546f5940..9eca8788908 100644
--- a/src/include/utils/dsa.h
+++ b/src/include/utils/dsa.h
@@ -97,7 +97,7 @@ typedef pg_atomic_uint64 dsa_pointer_atomic;
 #define DSA_DEFAULT_INIT_SEGMENT_SIZE ((size_t) (1 * 1024 * 1024))
 
 /* The minimum size of a DSM segment. */
-#define DSA_MIN_SEGMENT_SIZE	((size_t) (256 * 1024L))
+#define DSA_MIN_SEGMENT_SIZE	((size_t) (256 * 1024))
 
 /* The maximum size of a DSM segment. */
 #define DSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 532d6642bb4..1233e07d7da 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -17,9 +17,13 @@
 #include "utils/array.h"
 
 
-/* upper limit for GUC variables measured in kilobytes of memory */
-/* note that various places assume the byte size fits in a "long" variable */
-#if SIZEOF_SIZE_T > 4 && SIZEOF_LONG > 4
+/*
+ * Maximum for integer GUC variables that are measured in kilobytes of memory.
+ * This value is chosen to ensure that the corresponding number of bytes fits
+ * into a variable of type size_t or ssize_t.  Be sure to compute the number
+ * of bytes like "guc_var * (Size) 1024" to avoid int-width overflow.
+ */
+#if SIZEOF_SIZE_T > 4
 #define MAX_KILOBYTES	INT_MAX
 #else
 #define MAX_KILOBYTES	(INT_MAX / 1024)