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Commit7201cd1

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committed
Fix relptr's encoding of the base address.
Previously, we encoded both NULL and the first byte at the base addressas 0. That confusion led to the assertion in commite07d4dd, whichfailed when min_dynamic_shared_memory was used. Give them distinctencodings, by switching to 1-based offsets for non-NULL pointers. Alsoimprove macro hygiene in passing (missing/misplaced parentheses), andremove open-coded access to the raw offset value from freepage.c/h.Althoughe07d4dd was back-patched to 10, the only code that actuallymakes use of relptr at the base address arrived in84b1c63, so no needto 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
1 parentebc584e commit7201cd1

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3 files changed

+14
-11
lines changed

3 files changed

+14
-11
lines changed

‎src/backend/utils/mmgr/freepage.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -434,7 +434,7 @@ FreePageManagerDump(FreePageManager *fpm)
434434

435435
/* Dump general stuff. */
436436
appendStringInfo(&buf,"metadata: self %zu max contiguous pages = %zu\n",
437-
fpm->self.relptr_off,fpm->contiguous_pages);
437+
relptr_offset(fpm->self),fpm->contiguous_pages);
438438

439439
/* Dump btree. */
440440
if (fpm->btree_depth>0)
@@ -1269,7 +1269,7 @@ FreePageManagerDumpBtree(FreePageManager *fpm, FreePageBtree *btp,
12691269
if (btp->hdr.magic==FREE_PAGE_INTERNAL_MAGIC)
12701270
appendStringInfo(buf," %zu->%zu",
12711271
btp->u.internal_key[index].first_page,
1272-
btp->u.internal_key[index].child.relptr_off /FPM_PAGE_SIZE);
1272+
relptr_offset(btp->u.internal_key[index].child) /FPM_PAGE_SIZE);
12731273
else
12741274
appendStringInfo(buf," %zu(%zu)",
12751275
btp->u.leaf_key[index].first_page,
@@ -1859,7 +1859,7 @@ FreePagePopSpanLeader(FreePageManager *fpm, Size pageno)
18591859
{
18601860
Sizef=Min(span->npages,FPM_NUM_FREELISTS)-1;
18611861

1862-
Assert(fpm->freelist[f].relptr_off==pageno*FPM_PAGE_SIZE);
1862+
Assert(relptr_offset(fpm->freelist[f])==pageno*FPM_PAGE_SIZE);
18631863
relptr_copy(fpm->freelist[f],span->next);
18641864
}
18651865
}

‎src/include/utils/freepage.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -78,11 +78,11 @@ struct FreePageManager
7878
#definefpm_pointer_is_page_aligned(base,ptr)\
7979
(((Size) (((char *) (ptr)) - (base))) % FPM_PAGE_SIZE == 0)
8080
#definefpm_relptr_is_page_aligned(base,relptr)\
81-
((relptr).relptr_off % FPM_PAGE_SIZE == 0)
81+
(relptr_offset(relptr) % FPM_PAGE_SIZE == 0)
8282

8383
/* Macro to find base address of the segment containing a FreePageManager. */
8484
#definefpm_segment_base(fpm)\
85-
(((char *) fpm) - fpm->self.relptr_off)
85+
(((char *) fpm) -relptr_offset(fpm->self))
8686

8787
/* Macro to access a FreePageManager's largest consecutive run of pages. */
8888
#definefpm_largest(fpm) \

‎src/include/utils/relptr.h

Lines changed: 9 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -42,20 +42,23 @@
4242
#definerelptr_access(base,rp) \
4343
(AssertVariableIsOfTypeMacro(base, char *), \
4444
(__typeof__((rp).relptr_type)) ((rp).relptr_off == 0 ? NULL : \
45-
(base + (rp).relptr_off)))
45+
(base) + (rp).relptr_off - 1))
4646
#else
4747
/*
4848
* If we don't have __builtin_types_compatible_p, assume we might not have
4949
* __typeof__ either.
5050
*/
5151
#definerelptr_access(base,rp) \
5252
(AssertVariableIsOfTypeMacro(base, char *), \
53-
(void *) ((rp).relptr_off == 0 ? NULL : (base + (rp).relptr_off)))
53+
(void *) ((rp).relptr_off == 0 ? NULL : (base) + (rp).relptr_off - 1))
5454
#endif
5555

5656
#definerelptr_is_null(rp) \
5757
((rp).relptr_off == 0)
5858

59+
#definerelptr_offset(rp) \
60+
((rp).relptr_off - 1)
61+
5962
/* We use this inline to avoid double eval of "val" in relptr_store */
6063
staticinlineSize
6164
relptr_store_eval(char*base,char*val)
@@ -64,24 +67,24 @@ relptr_store_eval(char *base, char *val)
6467
return0;
6568
else
6669
{
67-
Assert(val>base);
68-
returnval-base;
70+
Assert(val >=base);
71+
returnval-base+1;
6972
}
7073
}
7174

7275
#ifdefHAVE__BUILTIN_TYPES_COMPATIBLE_P
7376
#definerelptr_store(base,rp,val) \
7477
(AssertVariableIsOfTypeMacro(base, char *), \
7578
AssertVariableIsOfTypeMacro(val, __typeof__((rp).relptr_type)), \
76-
(rp).relptr_off = relptr_store_eval(base, (char *) (val)))
79+
(rp).relptr_off = relptr_store_eval((base), (char *) (val)))
7780
#else
7881
/*
7982
* If we don't have __builtin_types_compatible_p, assume we might not have
8083
* __typeof__ either.
8184
*/
8285
#definerelptr_store(base,rp,val) \
8386
(AssertVariableIsOfTypeMacro(base, char *), \
84-
(rp).relptr_off = relptr_store_eval(base, (char *) (val)))
87+
(rp).relptr_off = relptr_store_eval((base), (char *) (val)))
8588
#endif
8689

8790
#definerelptr_copy(rp1,rp2) \

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