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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 really misbehave. However, analysis tools such as valgrind might whine about this; accordingly, let's band-aid relmapper.c to not do it. See also5b630501e
,d3f4e8a8a
,ad7b48ea0
, and other similar fixes. Apparently, none of those folk tried valgrinding initdb? This has been like this for long enough that I'm surprised it hasn't been reported before. Back-patch, just in case anybody wants to use a back branch on a platform that 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
vendored
11
src/backend/utils/cache/relmapper.c
vendored
@ -928,8 +928,15 @@ write_relmap_file(bool shared, RelMapFile *newmap,
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}
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}
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}
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/* Success, update permanent copy */
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/*
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memcpy(realmap, newmap, sizeof(RelMapFile));
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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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/* Critical section done */
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if (write_wal)
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if (write_wal)
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