gdb incorrectly performs modulo 32 on 64 bit operands for 'x' command

[George Shuklin]

https://stackoverflow.com/questions/50607748/how-to-force-gdb-to-view-at-a-given-address

$ gdb

(gdb) x 0x7f3ca4f68c20
0xa4f68c20: Cannot access memory at address 0xa4f68c20

Actual results: Attemp to read a value from 0xa4f68c20
Expected results: attempt to read a value from 0x7f3ca4f68c20.

This bug is present in GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git (bionic)

This bug does not present in GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1 (xenial)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gdb 8.1-0ubuntu3
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
Uname: Linux 4.15.0-22-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: X-Cinnamon
Date: Wed May 30 18:20:11 2018
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-20160624-2
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-06-22 (342 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 20160624-10:47
SourcePackage: gdb
UpgradeStatus: No upgrade log present (probably fresh install)