[Bug 2126577] Re: [26.04 FEAT] Set Architecture Level (ALS) to z15

[Launchpad Bug Tracker]

This bug was fixed in the package linux - 6.18.0-8.8

---------------
linux (6.18.0-8.8) resolute; urgency=medium

  * resolute/linux: 6.18.0-8.8 -proposed tracker (LP: #2136712)

  * Miscellaneous Ubuntu changes
    - [Packaging] disable signing for s390x

 -- Paolo Pisati <paolo.pisati at canonical.com>  Wed, 17 Dec 2025 15:20:04
+0100

** Changed in: linux (Ubuntu)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/2126577

Title:
  [26.04 FEAT] Set Architecture Level (ALS) to z15

Status in Ubuntu on IBM z Systems:
  Fix Committed
Status in gcc-15 package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in llvm-toolchain-20 package in Ubuntu:
  Fix Released
Status in llvm-toolchain-21 package in Ubuntu:
  Fix Released
Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  The IBM Z team requests to raise the architectural level set (ALS) for Ubuntu on IBM Z and LinuxONE (s390x) to z15, optimized for z16.
  For the gcc-15 compiler (and with that for user space) that would be in debian/rules2:
  march=z15
  mtune=z16
  For now gcc-15 (15.2) is the default in resolute.

  For the kernel that would be:
  debian.master/config/annotations
   CONFIG_MARCH_Z15                                policy<{'s390x': 'y'}>
   CONFIG_TUNE_Z16                                 policy<{'s390x': 'y'}>

  Changes in llvm are reflected in debian/rules like:
   # Change the default CPU for s390x
   ZARCH=z196
   ifeq ($(DERIVATIVE),Ubuntu)
    ifneq (,$(filter $(DISTRO), xenial bionic focal jammy noble plucky questing))
      ZARCH=z13
    else
      ZARCH=z15
    endif
   endif

  Also check the 'UTAH' based (ISO) image testing (QA Tracker).
  (Is the underlying system capable to execute the newly build binaries?).

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