[PATCH v3 0/3] support kselftest on nommu platform

[Hajime Tazaki <thehajime@gmail.com>]

This patchset adds an ability to execute kselftest on nommu platforms.

Currently there are several issues if we wish to run kselftests on nommu
targets:

- it cannot compile/build test binaries because the current files mainly
  assume to build with glibc,
- some of the tests are not able to run on nommu targets as there are no
  fork(2) syscall.

The first issue can be avoided if we can build static PIE binaries (if
targets support it), but in our case (build on ubuntu/glibc and run on
alpine/musl-libc), it fails to invoke due to lack of the GNU ifunc
mechanism.  Thus, we need to cross-compile with musl toolchain, which
needs to be solved the first issue.

The second issue is the lack of fork(2) syscall on those platforms.
Especially the test harness helper (kselftest_harness.h) uses the
syscall, which cannot be simply with vfork(2).  `timeout` command used
in `runner.sh` never works for nommu platform as it uses fork(2).

nommu component in the mm subsystem has several known issues and having
test cases should help this situation, thus this patchset is very first
step toward enriching test environment which has not been well tested
for a while.  The test cases is implemented based on the document
(Documentation/admin-guide/mm/nommu-mmap.rst).

Initial shape for this patches is implemented as an opt-in TARGET, not
built/invoked automatically if users don't specify this nommu target.

- v2:
https://lore.kernel.org/linux-mm/20260825015945.141739-1-thehajime@gmail.com/
- rfc:
https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/

Hajime Tazaki (3):
  selftests: kselftest: avoid cd - in runner
  selftests: run tests on nommu architecture
  selftests/nommu: add nommu mmap and mremap behavior tests

 Documentation/dev-tools/kselftest.rst         |  14 +
 tools/testing/selftests/kselftest/runner.sh   |   9 +-
 tools/testing/selftests/nommu/Makefile        |   8 +
 tools/testing/selftests/nommu/local.mk        |   7 +
 .../testing/selftests/nommu/nommu_mmap_test.c | 258 +++++++++++++
 .../selftests/nommu/nommu_mremap_test.c       | 362 ++++++++++++++++++
 6 files changed, 656 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/nommu/Makefile
 create mode 100644 tools/testing/selftests/nommu/local.mk
 create mode 100644 tools/testing/selftests/nommu/nommu_mmap_test.c
 create mode 100644 tools/testing/selftests/nommu/nommu_mremap_test.c


base-commit: e8d0f6a1b2a447d02845984fa6288787543cb03c
-- 
2.43.0