[Bug 2071468] Re: ELF package metadata failure: environment variable ‘DEB_HOST_ARCH’ not defined

[Benjamin Drung]

I started developing a fix for this bug:

Add an --encoded-package-metadata parameter to ld and change dpkg to
specify -Wl,--encoded-package-metadata=<encoded-json> instead of spec
file. PPA build for it:
https://launchpad.net/~bdrung/+archive/ubuntu/elf-package-metadata

Next step: Add this flag to the gold linker and submit those patches
upstream.

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https://bugs.launchpad.net/bugs/2071468

Title:
  ELF package metadata failure: environment variable ‘DEB_HOST_ARCH’ not
  defined

Status in asymptote package in Ubuntu:
  Fix Released
Status in curl package in Ubuntu:
  Fix Released
Status in dpkg package in Ubuntu:
  Triaged
Status in graphite2 package in Ubuntu:
  Fix Released
Status in gsequencer package in Ubuntu:
  Fix Released
Status in haskell-devscripts package in Ubuntu:
  Fix Released
Status in jose package in Ubuntu:
  New
Status in libreoffice package in Ubuntu:
  Fix Released
Status in libtpms package in Ubuntu:
  New
Status in mosh package in Ubuntu:
  Fix Released
Status in mwrap package in Ubuntu:
  Fix Released
Status in proftpd package in Ubuntu:
  New
Status in proftpd-dfsg package in Ubuntu:
  Fix Released
Status in serf package in Ubuntu:
  Fix Released
Status in speech-dispatcher package in Ubuntu:
  New
Status in squid package in Ubuntu:
  Fix Released
Status in swtpm package in Ubuntu:
  Fix Released
Status in texinfo package in Ubuntu:
  Triaged

Bug description:
  The ELF package note metadata introduced in dpkg 1.22.6ubuntu11
  (refined in 1.22.6ubuntu14) can cause this failure:

  ```
  gcc fatal error: environment variable ‘DEB_HOST_ARCH’ not defined
  ```

  This happens when the `-specs=/usr/share/dpkg/elf-package-
  metadata.specs` parameter is set but the needed environment variables
  are not set. Cases:

  1. Only the LDFLAGS is queried from dpkg-buildflags. Affected source
  packages builds: python3.12, openjdk-21, cdbs (causing dvbstreamer and
  rp-pppoe fail to build)

  2. autopkgtests

  3. debugging a crash of an application build with the -spec parameter

  4. People like to iteratively continue building the software in the
  build dir while hacking on the package and then have no environment
  variable set.

  This approach is too fragile. An alternative approach would be to specify the `--package-metadata` linker flag directly. The problem with that approach is that the curly brackets and quotation marks need to be escaped. Example failure: Building dpkg would add this parameter to the LDFLAGS:
  ```
  -Wl,--package-metadata,{"type":"deb","os":"ubuntu","name":"dpkg","version":"1.22.6ubuntu15","architecture":"amd64"}
  ```
  The following configure script call (non-relevant parameters deleted):
  ```
  $ gcc -Wl,--package-metadata,{type:deb,os:ubuntu,name:dpkg,version:1.22.6ubuntu15,architecture:amd64}
  /usr/bin/ld: cannot find {type:deb: No such file or directory
  /usr/bin/ld: cannot find os:ubuntu: No such file or directory
  /usr/bin/ld: cannot find name:dpkg: No such file or directory
  /usr/bin/ld: cannot find version:1.22.6ubuntu15: No such file or directory
  /usr/bin/ld: cannot find architecture:amd64}: No such file or directory
  ```

  Proposed solution: Add support for an `--escaped-package-metadata` parameter to the linkers that takes an URL encoded (RFC 3986) parameter. Example:
  ```
  -Wl,--encoded-package-metadata,%7B%22type%22:%22deb%22%2C%22os%22:%22ubuntu%22%2C%22name%22:%22dpkg%22%2C%22version%22:%221.22.6ubuntu15%22%2C%22architecture%22:%22amd64%22%7D
  ```

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