Work around spurious compiler warning in inet operators

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
index 42a4d9d44ec18375d3c382e04ebfa72ef8babbba..640fc37dc8319f4eeb248a3f41a5b9669a0327a5 100644 (file)
--- a/src/backend/utils/adt/network.c
+++ b/src/backend/utils/adt/network.c
@@ -1866,7 +1866,7 @@ 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);
@@ -1898,7 +1898,7 @@ 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));
@@ -1930,7 +1930,7 @@ 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));
@@ -1955,7 +1955,7 @@ 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);
@@ -2039,7 +2039,7 @@ inetmi(PG_FUNCTION_ARGS)
                unsigned char *pip2 = ip_addr(ip2);
                int                     carry = 1;
 
-               while (nb-- > 0)
+               while (--nb >= 0)
                {
                        int                     lobyte;