[PATCH v4 0/2] riscv: lib: add optimized memcmp() and extend KUnit tests

[Milan Tripkovic <milant2002@gmail.com>]

This v4 series introduces an optimized RISC-V memcmp() implementation 
and extends the KUnit string tests to cover both functional correctness 
and benchmarking of memcmp().

The memcmp() implementation incorporates review feedback from earlier 
versions. It features improved alignment handling, optimized loop 
structures, efficient use of the Zbb extension, and ensures overall 
correctness.

The KUnit updates provide comprehensive memcmp() test coverage and a 
benchmark mode. This v4 specifically fixes a build error regarding an 
undeclared function call (STRING_BENCH).

Signed-off-by: Milan Tripkovic <Milan.Tripkovic@rt-rk.com>

---
v4 changes:
    - Fixed build error: call to undeclared function 'STRING_BENCH'
    - Link to v3: https://lore.kernel.org/all/20260515141019.1234037-1-milant2002@gmail.com/

v3 changes:
    - Split memcmp benchmark into wrapper (string_bench_memcmp) and worker
      function (do_string_bench_memcmp).
    - Removed all C99 mixed declarations; moved all variable declarations
      to the top of each function.
    - Converted len, iterations and loop counters in the benchmark to u64
      to avoid implicit casts.
    - Cleaned up spacing, indentation and minor style issues.
    - Added #if defined(CONFIG_RISCV_ISA_ZBB)... in  memcmp.S
    - Link to v2: https://lore.kernel.org/all/20260514121359.931999-1-milant2002@gmail.com/

v2 changes:
    - Added alignment checks for buffers to avoid expensive misaligned loads.
    - Optimized the loop using end-pointers to reduce per-iteration overhead.
    - Implemented word-aligned tail handling using ZBB shifts.
    - Removed redundant pointer equality (a0 == a1) check.
    - Retained BE support via #ifndef; ZBB rev8 is used for the LE fast-path.
    - Fixed KUnit build failures for Clang and non-benchmark configs.
    - Link to v1: https://lore.kernel.org/all/20260512141007.1193033-1-milant2002@gmail.com/

Milan Tripkovic (2):
  riscv: lib: add memcmp() implementation
  lib/string_kunit: extend benchmarks and unit test to memcmp()

 arch/riscv/include/asm/string.h |   2 +
 arch/riscv/lib/Makefile         |   1 +
 arch/riscv/lib/memcmp.S         | 125 ++++++++++++++++++++++++++++++++
 arch/riscv/purgatory/Makefile   |   5 +-
 lib/tests/string_kunit.c        | 120 ++++++++++++++++++++++++++++++
 5 files changed, 252 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/lib/memcmp.S

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2.43.0