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Commit93ca02e

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Mark constantly allocated dest receiver as const.
This allows the compiler / linker to mark affected pages as read-only.Doing so requires casting constness away, as CreateDestReceiver()returns both constant and non-constant dest receivers. That's finethough, as any modification of the statically allocated receiverswould already have been a bug (and would now be caught on someplatforms).Discussion:https://postgr.es/m/20181015200754.7y7zfuzsoux2c4ya@alap3.anarazel.de
1 parentd1211c6 commit93ca02e

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1 file changed

+21
-12
lines changed

1 file changed

+21
-12
lines changed

‎src/backend/tcop/dest.c

Lines changed: 21 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -67,29 +67,33 @@ donothingCleanup(DestReceiver *self)
6767
*static DestReceiver structs for dest types needing no local state
6868
* ----------------
6969
*/
70-
staticDestReceiverdonothingDR= {
70+
staticconstDestReceiverdonothingDR= {
7171
donothingReceive,donothingStartup,donothingCleanup,donothingCleanup,
7272
DestNone
7373
};
7474

75-
staticDestReceiverdebugtupDR= {
75+
staticconstDestReceiverdebugtupDR= {
7676
debugtup,debugStartup,donothingCleanup,donothingCleanup,
7777
DestDebug
7878
};
7979

80-
staticDestReceiverprintsimpleDR= {
80+
staticconstDestReceiverprintsimpleDR= {
8181
printsimple,printsimple_startup,donothingCleanup,donothingCleanup,
8282
DestRemoteSimple
8383
};
8484

85-
staticDestReceiverspi_printtupDR= {
85+
staticconstDestReceiverspi_printtupDR= {
8686
spi_printtup,spi_dest_startup,donothingCleanup,donothingCleanup,
8787
DestSPI
8888
};
8989

90-
/* Globally available receiver for DestNone */
91-
DestReceiver*None_Receiver=&donothingDR;
92-
90+
/*
91+
* Globally available receiver for DestNone.
92+
*
93+
* It's ok to cast the constness away as any modification of the none receiver
94+
* would be a bug (which gets easier to catch this way).
95+
*/
96+
DestReceiver*None_Receiver= (DestReceiver*)&donothingDR;
9397

9498
/* ----------------
9599
*BeginCommand - initialize the destination at start of command
@@ -108,23 +112,28 @@ BeginCommand(const char *commandTag, CommandDest dest)
108112
DestReceiver*
109113
CreateDestReceiver(CommandDestdest)
110114
{
115+
/*
116+
* It's ok to cast the constness away as any modification of the none receiver
117+
* would be a bug (which gets easier to catch this way).
118+
*/
119+
111120
switch (dest)
112121
{
113122
caseDestRemote:
114123
caseDestRemoteExecute:
115124
returnprinttup_create_DR(dest);
116125

117126
caseDestRemoteSimple:
118-
return&printsimpleDR;
127+
returnunconstify(DestReceiver*,&printsimpleDR);
119128

120129
caseDestNone:
121-
return&donothingDR;
130+
returnunconstify(DestReceiver*,&donothingDR);
122131

123132
caseDestDebug:
124-
return&debugtupDR;
133+
returnunconstify(DestReceiver*,&debugtupDR);
125134

126135
caseDestSPI:
127-
return&spi_printtupDR;
136+
returnunconstify(DestReceiver*,&spi_printtupDR);
128137

129138
caseDestTuplestore:
130139
returnCreateTuplestoreDestReceiver();
@@ -146,7 +155,7 @@ CreateDestReceiver(CommandDest dest)
146155
}
147156

148157
/* should never get here */
149-
return&donothingDR;
158+
pg_unreachable();
150159
}
151160

152161
/* ----------------

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