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Commit53d4f5f

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Avoid memcpy() with same source and destination during relmapper init.
A narrow reading of the C standard says that memcpy(x,x,n) is undefined,although it's hard to envision an implementation that would reallymisbehave. However, analysis tools such as valgrind might whine aboutthis; accordingly, let's band-aid relmapper.c to not do it.See also5b63050,d3f4e8a,ad7b48e, and other similar fixes.Apparently, none of those folk tried valgrinding initdb? This has beenlike this for long enough that I'm surprised it hasn't been reportedbefore.Back-patch, just in case anybody wants to use a back branch on a platformthat complains about this; we back-patched those earlier fixes too.Discussion:https://postgr.es/m/161790.1608310142@sss.pgh.pa.us
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‎src/backend/utils/cache/relmapper.c

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -928,8 +928,15 @@ write_relmap_file(bool shared, RelMapFile *newmap,
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}
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}
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/* Success, update permanent copy */
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memcpy(realmap,newmap,sizeof(RelMapFile));
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/*
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* Success, update permanent copy. During bootstrap, we might be working
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* on the permanent copy itself, in which case skip the memcpy() to avoid
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* invoking nominally-undefined behavior.
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*/
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if (realmap!=newmap)
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memcpy(realmap,newmap,sizeof(RelMapFile));
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else
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Assert(!send_sinval);/* must be bootstrapping */
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/* Critical section done */
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if (write_wal)

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