[Bug 2052360] Re: empty /proc/cpuinfo can cause segfault

[dann frazier]

** Description changed:

  [Impact]
  cmake-extra's copyrighttest autopkgtest segfaults on armhf in our test infra:
-   https://objectstorage.prodstack5.canonical.com/swift/v1/0f9aae918d5b4744bf7b827671c86842/autopkgtest-jammy/jammy/armhf/c/cmake-extras/20240118_231525_552d3@/log.gz
+   https://objectstorage.prodstack5.canonical.com/swift/v1/0f9aae918d5b4744bf7b827671c86842/autopkgtest-jammy/jammy/armhf/c/cmake-extras/20240118_231525_552d3@/log.gz
  
  This is because /proc/cpuinfo appears to be empty, which triggers an
  underflow condition. This doesn't impact all architectures - it may be
  limited to armhf containers running on arm64 hosts.
  
  This presumably impacts the building of any software using the
  CopyrightTest module provided by cmake-extra in a similar environment.
  
  [Test Case]
  Launch an armhf lxd jammy container and run the autopkgtest for cmake-extras within:
  
- ubuntu at armhf:~/cmake-extras-1.6$ ./debian/tests/copyrighttest 
+ ubuntu at armhf:~/cmake-extras-1.6$ ./debian/tests/copyrighttest
  + set -ep
  + mktemp --tmpdir=/tmp -d
  + builddir=/tmp/tmp.106fU16BhF
  + trap rm -rf /tmp/tmp.106fU16BhF 0 INT QUIT ABRT PIPE TERM
  + pwd
  + srcdir=/home/ubuntu/cmake-extras-1.6/examples/copyrighttest-demo
  + cd /tmp/tmp.106fU16BhF
  + cmake /home/ubuntu/cmake-extras-1.6/examples/copyrighttest-demo
  -- The C compiler identification is GNU 11.4.0
  -- The CXX compiler identification is GNU 11.4.0
  -- Detecting C compiler ABI info
  -- Detecting C compiler ABI info - done
  -- Check for working C compiler: /usr/bin/cc - skipped
  -- Detecting C compile features
  -- Detecting C compile features - done
  -- Detecting CXX compiler ABI info
  -- Detecting CXX compiler ABI info - done
  -- Check for working CXX compiler: /usr/bin/c++ - skipped
  -- Detecting CXX compile features
  -- Detecting CXX compile features - done
  terminate called after throwing an instance of 'std::length_error'
-   what():  basic_string::_M_replace_aux
+   what():  basic_string::_M_replace_aux
  Aborted (core dumped)
  + rm -rf /tmp/tmp.106fU16BhF
  ubuntu at armhf:~/cmake-extras-1.6$
  
  [What Could Go Wrong]
- Perhaps there is some evil AI out there that only has access to lxd containers for building its self-generated code. That AI could also be somehow bound to rules held over from its corporate origins that require it avoid violating human IP laws, and it therefore always does a scan using cmake-extras' CopyrightTestConfig module. This segfault could then have been the only thing standing in its way from achieving its world domination plans.
+ The upstream fix now emits an errors message when an empty /proc/cpuinfo file is found. This error message is not expected by cmake's built-in tests, causing those tests to fail. It may impact other tests as well. Though it should only be emitted in environments where cmake would otherwise crash.

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https://bugs.launchpad.net/bugs/2052360

Title:
  empty /proc/cpuinfo can cause segfault

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