[Bug 1971612] Re: [UBUNTU 22.04] GLIBC: Adding new s390 platform IBM z16

[bugproxy]

------- Comment From STLI at de.ibm.com 2022-07-12 05:14 EDT-------
I've just installed the package on z15/z16:
$ apt list --installed libc6
libc6/jammy-proposed,now 2.35-0ubuntu3.1 s390x [installed]

I've placed some test-libraries into these paths:
$ find /usr/lib/s390x-linux-gnu/glibc-hwcaps -type f
/usr/lib/s390x-linux-gnu/glibc-hwcaps/z13/libtest-glibc-hwcaps-lib.so
/usr/lib/s390x-linux-gnu/glibc-hwcaps/z14/libtest-glibc-hwcaps-lib.so
/usr/lib/s390x-linux-gnu/glibc-hwcaps/z15/libtest-glibc-hwcaps-lib.so
/usr/lib/s390x-linux-gnu/glibc-hwcaps/z16/libtest-glibc-hwcaps-lib.so

Depending on the machine-level, the correct library is used, e.g.:
- on z16, /usr/lib/s390x-linux-gnu/glibc-hwcaps/z16/libtest-glibc-hwcaps-lib.so
- on z16, if .../glibc-hwcaps/z16/... is not present: /usr/lib/s390x-linux-gnu/glibc-hwcaps/z15/libtest-glibc-hwcaps-lib.so

- on z15, /usr/lib/s390x-linux-gnu/glibc-hwcaps/z15/libtest-glibc-
hwcaps-lib.so

Thanks for integrating the patches. This bug is successfully verified
for jammy.

** Tags removed: verification-needed-jammy
** Tags added: verification-done-jammy

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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:
  Fix Committed
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.

   * Test of the glibc-hwcaps feature is covered 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.

   * IBM is going to test this feature on a z16 as soon as a patched
     libc6 package is available.

  [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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