Work around spurious compiler warning in inet operators

anarazel · anarazel · commit a7a92738ffce · 2023-03-16T14:48:46.000-07:00
gcc 12+ has complaints like the following: ../../../../../pgsql/src/backend/utils/adt/network.c: In function 'inetnot': ../../../../../pgsql/src/backend/utils/adt/network.c:1893:34: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=] 1893 | pdst[nb] = ~pip[nb]; | ~~~~~~~~~^~~~~~~~~~ ../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16 27 | unsigned char ipaddr[16]; /* up to 128 bits of address */ | ^~~~~~ ../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16 This is due to a compiler bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104986 It has been a year since the bug has been reported without getting fixed. As the warnings are verbose and use of gcc 12 is becoming more common, it seems worth working around the bug. Particularly because a simple reformulation of the loop condition fixes the issue and isn't any less readable. Author: Tom Lane <tgl@sss.pgh.pa.us> Author: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/144536.1648326206@sss.pgh.pa.us Backpatch: 11-
diff --git a/src/backend/utils/adt/network.c b/src/backend/utils/adt/network.c
@@ -1889,7 +1889,7 @@ inetnot(PG_FUNCTION_ARGS)
 		unsigned char *pip = ip_addr(ip);
 		unsigned char *pdst = ip_addr(dst);
 
-		while (nb-- > 0)
+		while (--nb >= 0)
 			pdst[nb] = ~pip[nb];
 	}
 	ip_bits(dst) = ip_bits(ip);
@@ -1921,7 +1921,7 @@ inetand(PG_FUNCTION_ARGS)
 		unsigned char *pip2 = ip_addr(ip2);
 		unsigned char *pdst = ip_addr(dst);
 
-		while (nb-- > 0)
+		while (--nb >= 0)
 			pdst[nb] = pip[nb] & pip2[nb];
 	}
 	ip_bits(dst) = Max(ip_bits(ip), ip_bits(ip2));
@@ -1953,7 +1953,7 @@ inetor(PG_FUNCTION_ARGS)
 		unsigned char *pip2 = ip_addr(ip2);
 		unsigned char *pdst = ip_addr(dst);
 
-		while (nb-- > 0)
+		while (--nb >= 0)
 			pdst[nb] = pip[nb] | pip2[nb];
 	}
 	ip_bits(dst) = Max(ip_bits(ip), ip_bits(ip2));
@@ -1978,7 +1978,7 @@ internal_inetpl(inet *ip, int64 addend)
 		unsigned char *pdst = ip_addr(dst);
 		int			carry = 0;
 
-		while (nb-- > 0)
+		while (--nb >= 0)
 		{
 			carry = pip[nb] + (int) (addend & 0xFF) + carry;
 			pdst[nb] = (unsigned char) (carry & 0xFF);
@@ -2062,7 +2062,7 @@ inetmi(PG_FUNCTION_ARGS)
 		unsigned char *pip2 = ip_addr(ip2);
 		int			carry = 1;
 
-		while (nb-- > 0)
+		while (--nb >= 0)
 		{
 			int			lobyte;
 
