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Commit88f626f

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Fix more DSA problems uncovered by the buildfarm.
On 32-bit systems, don't try to use 64-bit DSA pointers, because thecomputation of DSA_MAX_SEGMENT_SIZE overflows Size.Cast 1 to Size before shifting it, so that the compiler doesn'tproduce a result of the wrong width.In passing, change one use of size_t to Size.
1 parent670b3bc commit88f626f

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2 files changed

+16
-11
lines changed

2 files changed

+16
-11
lines changed

‎src/backend/utils/mmgr/dsa.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -98,7 +98,7 @@
9898
#defineDSA_OFFSET_BITMASK (((dsa_pointer) 1 << DSA_OFFSET_WIDTH) - 1)
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100100
/* The maximum size of a DSM segment. */
101-
#defineDSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
101+
#defineDSA_MAX_SEGMENT_SIZE ((Size) 1 << DSA_OFFSET_WIDTH)
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103103
/* Number of pages (see FPM_PAGE_SIZE) per regular superblock. */
104104
#defineDSA_PAGES_PER_SUPERBLOCK16
@@ -1919,7 +1919,7 @@ get_best_segment(dsa_area *area, Size npages)
19191919
* The minimum contiguous size that any segment in this bin should
19201920
* have. We'll re-bin if we see segments with fewer.
19211921
*/
1922-
Sizethreshold=1 << (bin-1);
1922+
Sizethreshold=(Size)1 << (bin-1);
19231923
dsa_segment_indexsegment_index;
19241924

19251925
/* Search this bin for a segment with enough contiguous space. */

‎src/include/utils/dsa.h

Lines changed: 14 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -24,20 +24,25 @@ struct dsa_area;
2424
typedefstructdsa_areadsa_area;
2525

2626
/*
27-
* If this system doesn't support atomic operations on 64 bit values then
28-
* we fall back to 32 bit dsa_pointer. For testing purposes,
29-
* USE_SMALL_DSA_POINTER can be defined to force the use of 32 bit
30-
* dsa_pointer even on systems that support 64 bit atomics.
27+
* If this system only uses a 32-bit value for Size, then use the 32-bit
28+
* implementation of DSA. This limits the amount of DSA that can be created
29+
* to something significantly less than the entire 4GB address space because
30+
* the DSA pointer must encode both a segment identifier and an offset, but
31+
* that shouldn't be a significant limitation in practice.
32+
*
33+
* If this system doesn't support atomic operations on 64-bit values, then
34+
* we fall back to 32-bit dsa_pointer for lack of other options.
35+
*
36+
* For testing purposes, USE_SMALL_DSA_POINTER can be defined to force the use
37+
* of 32-bit dsa_pointer even on systems capable of supporting a 64-bit
38+
* dsa_pointer.
3139
*/
32-
#ifndefPG_HAVE_ATOMIC_U64_SUPPORT
33-
#defineSIZEOF_DSA_POINTER 4
34-
#else
35-
#ifdefUSE_SMALL_DSA_POINTER
40+
#ifSIZEOF_SIZE_T==4|| !defined(PG_HAVE_ATOMIC_U64_SUPPORT)|| \
41+
defined(USE_SMALL_DSA_POINTER)
3642
#defineSIZEOF_DSA_POINTER 4
3743
#else
3844
#defineSIZEOF_DSA_POINTER 8
3945
#endif
40-
#endif
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4247
/*
4348
* The type of 'relative pointers' to memory allocated by a dynamic shared

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