[Bug 1971612] Comment bridged from LTC Bugzilla

[bugproxy]

------- Comment From STLI at de.ibm.com 2022-07-05 04:17 EDT-------
[Impact]

The first part of z16 support went into glibc-2.34:
- glibc commit "S390: Add new hwcap values."
https://sourceware.org/git/?p=glibc.git;a=commit;h=25251c0707fe34f30a27381a5fabc35435a96621

After IBM z16 has been announced, we need to add the new s390 platform in glibc:
- glibc upstream commit "S390: Add new s390 platform z16."
https://sourceware.org/git/?p=glibc.git;a=commit;h=2376944b9e5c0364b9fb473e4d8dabca31b57167
- Backport to glibc 2.35 release branch:
https://sourceware.org/git/?p=glibc.git;a=commit;h=6583d534458e7f8beec8d0766b6db0bdaae6749c

Beneath adding the platform name, the glibc-hwcaps subdirectories
feature is extended. The z16 subfolder is now also searched for "z16"
specific libraries if support is indicated by the HWCAPs.

[Test Plan]

Testing of the glibc-hwcaps feature is done by tst-glibc-hwcaps.c test from glibc-testsuite. In short: Different shared libraries are placed in the z16/z15/... subdirectories. A runtime-check tests whether the correct library was loaded on the particular machine.
Yes, IBM will test this feature on a z16 as soon as the libc packages are updated.

[Where problems could occur]

The mentioned patch does only change s390. Other architectures are not
involved.

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https://bugs.launchpad.net/bugs/1971612

Title:
  [UBUNTU 22.04] GLIBC: Adding new s390 platform IBM z16

Status in Ubuntu on IBM z Systems:
  In Progress
Status in glibc package in Ubuntu:
  New
Status in glibc source package in Impish:
  Won't Fix
Status in glibc source package in Jammy:
  In Progress
Status in glibc source package in Kinetic:
  New

Bug description:
  SRU Justification:
  ==================

  [Impact]

   * This is a hardware enablement SRU to improve IBM z16 support.

   * A fatal glibc error is dumped if glibc was build with an
     architecture level set for z16, but run on an older machine.
     (See dl-hwcap-check.h.)

   * Hence z16 is added as new s390 platform,

   * the new IBM z16 is added to platform string array,

   * the macro _DL_PLATFORMS_COUNT is incremented.

   * '_dl_hwcaps_subdir' is extended by "z16" if HWCAP_S390_VXRS_PDE2
     is set,

   * and 'tst-glibc-hwcaps.c' is extended in order to test z16 via
     new marker5.

  [Test Plan]

   * An IBM zSystems (or LinuxONE) system,
     with Ubuntu 22.04 LTS installed.

   * Install the updated libc6 package on different zSystems
     hardware generations for regression testing, since
     the patched libc6 should not cause any changed behavior
     or impact on existing IBM zSystems hardware.

   * Run for example the Canonical server certification test suite
     to create meaningful load on such a system,
     or a bug specific test case.

  [Where problems could occur]

   * There could be problems with the newly introduced marker5
     (libmarkermod5-1.so) in sysdeps/s390/s390-64/Makefile.
     These should largely occur already at build time,
     or in 'tst-glibc-hwcaps.c'.

   * The increased 'DL_PLATFORMS_COUNT' shouldn't harm.

   * Problems could occur is the hardware capabilities (hwcap) are not properly
     identified at 'dl-hwcap-check.h' and 'dl-hwcaps-subdirs.c'.

   * Wrong (not existing) capabilities might be assumed that could
     eventually lead to crashes in attempts to use them.

   * The majority of the changes are under sysdeps/s390 and with that
     hardware specific, other are in script and Makefile.

  [Other Info]
   
   * IBM z16 exploitation is introduced with 22.04 LTS, hence
     this patch is not needed for older Ubuntu releases.
  __________

  After IBM z16 has been announced, we need to add the new s390 platform
  in glibc.

  S390: Add new s390 platform z16.
  https://sourceware.org/git/?p=glibc.git;a=commit;h=2376944b9e5c0364b9fb473e4d8dabca31b57167

  Backport to glibc 2.35 release branch:
  https://sourceware.org/git/?p=glibc.git;a=commit;h=6583d534458e7f8beec8d0766b6db0bdaae6749c

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