GDB cannot evaluate hexadecimal floating-point numbers with negative exponent

[Hugues de Lassus Saint-Geniès]

Trying to print a hexadecimal floating-point number evaluates to a wrong double.
This makes fp-based programs harder to debug.
In the example below, the parser seems to recognize 0xa.0p as (double)10 and 4 as an int, and a subtraction '-', thus the result '6'.

GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
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(gdb) print /f 0xa.0p-4
$1 = 6

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: gdb 7.7.1-0ubuntu5~14.04.2
ProcVersionSignature: Ubuntu 3.13.0-49.83-generic 3.13.11-ckt17
Uname: Linux 3.13.0-49-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.14.1-0ubuntu3.10
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Apr 24 15:43:39 2015
InstallationDate: Installed on 2014-11-06 (168 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: gdb
UpgradeStatus: No upgrade log present (probably fresh install)

[Hugues de Lassus Saint-Geniès (huguesdelassus)]

A bug was filed on Sourceware Bugzilla for GDB at https://www.sourceware.org/bugzilla/show_bug.cgi?id=18318 as it affects GDB 7.9 too.