[Bug 1521081] Re: wrong "maybe-uninitialized" warning with -O3 (when building goplay)

[Matthias Klose]

I doubt this is ppc specific, but triggered by -O3 instead.

** Summary changed:

- wrong "maybe-uninitialized" warning on ppc64el only (when building goplay)
+ wrong "maybe-uninitialized" warning with -O3 (when building goplay)

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Title:
  wrong "maybe-uninitialized" warning with -O3 (when building goplay)

Status in gcc-5 package in Ubuntu:
  New

Bug description:
  goplay FTBFS on ppc64el  with:

  g++ -DHAVE_CONFIG_H -I. -I.. -I.. -I/usr/include/tagcoll-2.0.14 -Wall -Werror -ggdb    -g -O3 -fstack-protector-strong -Wformat -Werror=format-security -std=c++11 -c -o XDGDesktopEntry.o XDGDesktopEntry.cpp
  XDGDesktopEntry.cpp: In member function 'int XDGDesktopEntry::run(const char*)':
  XDGDesktopEntry.cpp:655:17: error: 'value' may be used uninitialized in this function [-Werror=maybe-uninitialized]
        if (value[i] == 'i') {
                   ^
  cc1plus: all warnings being treated as errors

  
  full build log: https://launchpadlibrarian.net/227946515/buildlog_ubuntu-xenial-ppc64el.goplay_0.9.1%2Bnmu1_BUILDING.txt.gz

  This does not make much sense to me. The code:

      // Now run the desktop file
      getEntry("Exec", NULL, &value);

      // XXX: For now, just remove the field codes...
      std::string commandString;
      for(unsigned int i = 0; value[i] != '\0'; i++) {
         if (value[i] == '%') {
               i++;
               if (value[i] == 'i') {

  value is a "const char*" and gets initialized in the getEntry(). Even
  *if* there was a reason to argue that value might be uninitialized,
  then the complaint should already be for the "for" loop. There is no
  reason why value should be valid in the "for" loop and for the
  "value[i] == '%'" check, but after incrementing just "i" it would
  suddenly not be any more.

  It builds fine on Debian ppc64el
  (https://buildd.debian.org/status/fetch.php?pkg=goplay&arch=ppc64el&ver=0.9.1%2Bnmu1&stamp=1448818386)
  and on all other Ubuntu architectures. So this seems to be specific to
  gcc-5 on Ubuntu on ppc64el.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: gcc-5 5.2.1-26ubuntu1
  ProcVersionSignature: Ubuntu 4.2.0-19.23-generic 4.2.6
  Uname: Linux 4.2.0-19-generic x86_64
  ApportVersion: 2.19.2-0ubuntu8
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Mon Nov 30 08:19:47 2015
  EcryptfsInUse: Yes
  SourcePackage: gcc-5
  UpgradeStatus: No upgrade log present (probably fresh install)

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