[Bug 2108968] Re: Enable -fzero-init-padding-bits=all, -Wbidi-chars=any

[Julian Andres Klode]

We likely have to postpone the changes for dpkg to the next release
cycle as we need to prioritize work on coreutils over the visuals of our
build logs and ease of disabling these options (which so far nobody has
asked for).

The former would have been easy and is what I had planned for, but doko
specifically requested the ability to also disable these flags via build
options and that requires significantly more effort.

The next steps here are to come up with flag names and propose them to
debian-dpkg and get a consensus before moving forward with implementing
them. The initial patch can be found in

https://git.launchpad.net/~juliank/ubuntu/+source/dpkg/commit/?id=3ebdfb178dd9498c34a1095e5cbe474b0faf6d4e

but my conversation with doko suggests these need to move to Debian.pm
or some more stuff is needed there to register the flags (hence why it
needs coordinating).

Also without coordination it would only be usable in Ubuntu deltas,
which would incur more overhead if anyone actually used the option.

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https://bugs.launchpad.net/bugs/2108968

Title:
  Enable -fzero-init-padding-bits=all, -Wbidi-chars=any

Status in dpkg package in Ubuntu:
  Confirmed
Status in gcc-15 package in Ubuntu:
  Fix Released

Bug description:
  Hello, please consider this *untested* debdiff that I hope would
  enable -fzero-init-padding-bits=all and -Wbidi-chars=any in the
  Ubuntu-specific GCC specs.

  The first option, -fzero-init-padding-bits=all, is asking the compiler
  to zero out bits in unions and structs. GCC 15 moved to a more
  standards-compliant implementation
  https://gcc.gnu.org/gcc-15/changes.html -- we could bring back the GCC
  14 behavior with -fzero-init-padding-bits=unions but the option of
  zeroing even the unused padding bits is available to us now, I believe
  we should use it. https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-
  Options.html#index-fzero-init-padding-bits_003dvalue

  The second option, -Wbidi-chars=any, brings no runtime security
  benefits. Instead, it will log instances of potentially malicious use
  of Unicode bidirectional characters that can mask malicious code from
  human inspection. I hope some day we could scrape the logs to discover
  abuse. https://best.openssf.org/Compiler-Hardening-Guides/Compiler-
  Options-Hardening-Guide-for-C-and-C++#enable-warnings-for-possibly-
  misleading-unicode-bidirectional-control-characters
  https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wbidi-
  chars_003d

  I tried to introduce -fhardened (
  https://bugs.launchpad.net/ubuntu/+source/gcc-14/+bug/2080267 ,
  https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-
  Hardening-Guide-for-C-and-C++#enable-pre-determined-set-of-hardening-
  options-in-gcc ) but ran into significant problems. We should have a
  conversation about it. I was really hoping -fhardened could address
  https://bugs.launchpad.net/ubuntu/+source/gcc-14/+bug/2078989 -- and I
  think it would -- but the -Whardened warning messages (
  https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-
  Hardening-Guide-for-C-and-C++#additional-considerations-6 ) are
  obnoxious enough that we can't possibly ship the implementation that I
  came up with.

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