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Prevent using strncpy with src == dest in TupleDescInitEntry.

The C and POSIX standards state that strncpy's behavior is undefined whensource and destination areas overlap. While it remains dubious whether anyimplementations really misbehave when the pointers are exactly equal, someplatforms are now starting to force the issue by complaining when anundefined call occurs. (In particular OS X 10.9 has been seen to dump corehere, though the exact set of circumstances needed to trigger that remainelusive. Similar behavior can be expected to be optional on Linux andother platforms in the near future.) So tweak the code to explicitly donothing when nothing need be done.Back-patch to all active branches. In HEAD, this also lets us get rid ofan exception in valgrind.supp.Per discussion of a report from Matthias Schmitt.

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src
- backend/access/common
  - tupdesc.c
- tools
  - valgrind.supp

2 files changed

+10

-20

lines changed

`‎src/backend/access/common/tupdesc.c`

Lines changed: 10 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -468,6 +468,12 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)`
`468`	`468`	`*This function initializes a single attribute structure in`
`469`	`469`	`*a previously allocated tuple descriptor.`
`470`	`470`	`*`
	`471`	`+ * If attributeName is NULL, the attname field is set to an empty string`
	`472`	`+ * (this is for cases where we don't know or need a name for the field).`
	`473`	`+ * Also, some callers use this function to change the datatype-related fields`
	`474`	`+ * in an existing tupdesc; they pass attributeName = NameStr(att->attname)`
	`475`	`+ * to indicate that the attname field shouldn't be modified.`
	`476`	`+ *`
`471`	`477`	`* Note that attcollation is set to the default for the specified datatype.`
`472`	`478`	`* If a nondefault collation is needed, insert it afterwards using`
`473`	`479`	`* TupleDescInitEntryCollation.`
`@@ -501,12 +507,12 @@ TupleDescInitEntry(TupleDesc desc,`
`501`	`507`	`/*`
`502`	`508`	`* Note: attributeName can be NULL, because the planner doesn't always`
`503`	`509`	`* fill in valid resname values in targetlists, particularly for resjunk`
`504`		`- * attributes.`
	`510`	`+ * attributes. Also, do nothing if caller wants to re-use the old attname.`
`505`	`511`	`*/`
`506`		`-if (attributeName!=NULL)`
`507`		`-namestrcpy(&(att->attname),attributeName);`
`508`		`-else`
	`512`	`+if (attributeName==NULL)`
`509`	`513`	`MemSet(NameStr(att->attname),0,NAMEDATALEN);`
	`514`	`+elseif (attributeName!=NameStr(att->attname))`
	`515`	`+namestrcpy(&(att->attname),attributeName);`
`510`	`516`
`511`	`517`	`att->attstattarget=-1;`
`512`	`518`	`att->attcacheoff=-1;`

`‎src/tools/valgrind.supp`

Lines changed: 0 additions & 16 deletions

Original file line number	Diff line number	Diff line change
`@@ -64,22 +64,6 @@`
`64`	`64`	`}`
`65`	`65`
`66`	`66`
`67`		`-# resolve_polymorphic_tupdesc(), a subroutine of internal_get_result_type(),`
`68`		`-# can instigate a memcpy() call where the two pointer arguments are exactly`
`69`		`-# equal. The behavior thereof is formally undefined, but implementations`
`70`		`-# where it's anything other than a no-op are thought unlikely.`
`71`		`-{`
`72`		`-noopmemcpy_internal_get_result_type`
`73`		`-Memcheck:Overlap`
`74`		`-`
`75`		`-fun:strncpy`
`76`		`-fun:namestrcpy`
`77`		`-fun:TupleDescInitEntry`
`78`		`-...`
`79`		`-fun:internal_get_result_type`
`80`		`-}`
`81`		`-`
`82`		`-`
`83`	`67`	`# gcc on ppc64 can generate a four-byte read to fetch the final "char" fields`
`84`	`68`	`# of a FormData_pg_cast. This is valid compiler behavior, because a proper`
`85`	`69`	`# FormData_pg_cast has trailing padding. Tuples we treat as structures omit`

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Commit9a9473f

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2 files changed

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`‎src/backend/access/common/tupdesc.c`

`‎src/tools/valgrind.supp`

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