[Question] Documentation/features: More automation/scripting help?

[Andrea Parri <andrea.parri@amarulasolutions.com>]

Hi all,

The directory (not yet three years old although, I freely admit, I've
only recently become aware of it) provides arch. support matrices for
more than 40 generic kernel features that need per-arch. support:

This is a superb project! ;-)  and not a simple one given that, to be
effective, this requires the prompt collaboration between (the intere-
sted) features maintainers/developers, every architecture maintainers,
and documentation maintainers.

There currently appear to be some mismatches between such doc and the
the actual state of the code (e.g., missing architecture, feature not
existing anymore, status flags out-of-date). Realized this, I started
to patch the doc, but this process became soon tedious (consider also
that I barely know what some of these features are about...).

Hence this post. I am wondering if it would make sense to script some
of these matrices.  So, rather than (or together with) using the cur-
rently hard-coded matrices, try to (automatically) generate them from
the sources/configs. Consider the sketch below (sorry for the raw sh).

diff --git a/Documentation/features/list-arch.sh b/Documentation/features/list-arch.sh
index c16b5b5956889..cdec0c1db9db2 100755
--- a/Documentation/features/list-arch.sh
+++ b/Documentation/features/list-arch.sh
@@ -18,7 +18,13 @@ for F in */*/arch-support.txt; do
   C=$(grep -h "^#         Kconfig:"     $F | cut -c25-)
   D=$(grep -h "^#         description:" $F | cut -c25-)
   S=$(grep -hw $ARCH $F | cut -d\| -f3)
+  myS=$(grep -h $C ../../arch/$ARCH/Kconfig)
+  if [ -z "$myS" ]; then
+	  myS=" -- "
+  else
+	  myS=" ok "
+  fi
 
-  printf "%10s/%-22s:%s| %35s # %s\n" "$SUBSYS" "$N" "$S" "$C" "$D"
+  printf "%10s/%-22s:%s VS. %s| %35s # %s\n" "$SUBSYS" "$N" "$S" "$myS" "$C" "$D"
 done
 

With this diff.,

andrea@andrea:~$ ./Documentation/features/list-arch.sh riscv > /tmp/riscv.txt
grep: asm/rwsem.h: No such file or directory
andrea@andrea:~$ cat /tmp/riscv.txt
#
# Kernel feature support matrix of the 'riscv' architecture:
#
      core/ BPF-JIT              : VS.  -- |                        HAVE_BPF_JIT #  arch supports BPF JIT optimizations
      core/ generic-idle-thread  : VS.  ok |             GENERIC_SMP_IDLE_THREAD #  arch makes use of the generic SMP idle thread facility
      core/ jump-labels          : VS.  -- |                HAVE_ARCH_JUMP_LABEL #  arch supports live patched, high efficiency branches
      core/ tracehook            : VS.  ok |                 HAVE_ARCH_TRACEHOOK #  arch supports tracehook (ptrace) register handling APIs
     debug/ gcov-profile-all     : VS.  -- |           ARCH_HAS_GCOV_PROFILE_ALL #  arch supports whole-kernel GCOV code coverage profiling
     debug/ KASAN                : VS.  -- |                     HAVE_ARCH_KASAN #  arch supports the KASAN runtime memory checker
     debug/ kgdb                 : VS.  -- |                      HAVE_ARCH_KGDB #  arch supports the kGDB kernel debugger
     debug/ kprobes              : VS.  ok |                        HAVE_KPROBES #  arch supports live patched kernel probe
     debug/ kprobes-on-ftrace    : VS.  -- |              HAVE_KPROBES_ON_FTRACE #  arch supports combined kprobes and ftrace live patching
     debug/ kretprobes           : VS.  -- |                     HAVE_KRETPROBES #  arch supports kernel function-return probes
     debug/ optprobes            : VS.  -- |                      HAVE_OPTPROBES #  arch supports live patched optprobes
     debug/ stackprotector       : VS.  -- |              HAVE_CC_STACKPROTECTOR #  arch supports compiler driven stack overflow protection
     debug/ uprobes              : VS.  -- |               ARCH_SUPPORTS_UPROBES #  arch supports live patched user probes
     debug/ user-ret-profiler    : VS.  -- |           HAVE_USER_RETURN_NOTIFIER #  arch supports user-space return from system call profiler
        io/ dma-api-debug        : VS.  ok |                  HAVE_DMA_API_DEBUG #  arch supports DMA debug facilities
        io/ dma-contiguous       : VS.  ok |                 HAVE_DMA_CONTIGUOUS #  arch supports the DMA CMA (continuous memory allocator)
        io/ sg-chain             : VS.  -- |                   ARCH_HAS_SG_CHAIN #  arch supports chained scatter-gather lists
       lib/ strncasecmp          : VS.  -- |             __HAVE_ARCH_STRNCASECMP #  arch provides an optimized strncasecmp() function
   locking/ cmpxchg-local        : VS.  -- |                  HAVE_CMPXCHG_LOCAL #  arch supports the this_cpu_cmpxchg() API
   locking/ lockdep              : VS.  -- |                     LOCKDEP_SUPPORT #  arch supports the runtime locking correctness debug facility
   locking/ queued-rwlocks       : VS.  -- |             ARCH_USE_QUEUED_RWLOCKS #  arch supports queued rwlocks
   locking/ queued-spinlocks     : VS.  -- |           ARCH_USE_QUEUED_SPINLOCKS #  arch supports queued spinlocks
   locking/ rwsem-optimized      : VS.  -- |               Optimized asm/rwsem.h #  arch provides optimized rwsem APIs
      perf/ kprobes-event        : VS.  -- |      HAVE_REGS_AND_STACK_ACCESS_API #  arch supports kprobes with perf events
      perf/ perf-regs            : VS.  -- |                      HAVE_PERF_REGS #  arch supports perf events register access
      perf/ perf-stackdump       : VS.  -- |           HAVE_PERF_USER_STACK_DUMP #  arch supports perf events stack dumps
     sched/ membarrier-sync-core : VS.  -- |       ARCH_HAS_MEMBARRIER_SYNC_CORE #  arch supports core serializing membarrier
     sched/ numa-balancing       : VS.  -- |        ARCH_SUPPORTS_NUMA_BALANCING #  arch supports NUMA balancing
   seccomp/ seccomp-filter       : VS.  -- |            HAVE_ARCH_SECCOMP_FILTER #  arch supports seccomp filters
      time/ arch-tick-broadcast  : VS.  -- |             ARCH_HAS_TICK_BROADCAST #  arch provides tick_broadcast()
      time/ clockevents          : VS.  ok |                 GENERIC_CLOCKEVENTS #  arch support generic clock events
      time/ context-tracking     : VS.  -- |               HAVE_CONTEXT_TRACKING #  arch supports context tracking for NO_HZ_FULL
      time/ irq-time-acct        : VS.  -- |            HAVE_IRQ_TIME_ACCOUNTING #  arch supports precise IRQ time accounting
      time/ modern-timekeeping   : VS.  -- |            !ARCH_USES_GETTIMEOFFSET #  arch does not use arch_gettimeoffset() anymore
      time/ virt-cpuacct         : VS.  -- |            HAVE_VIRT_CPU_ACCOUNTING #  arch supports precise virtual CPU time accounting
        vm/ ELF-ASLR             : VS.  -- |              ARCH_HAS_ELF_RANDOMIZE #  arch randomizes the stack, heap and binary images of ELF binaries
        vm/ huge-vmap            : VS.  -- |                 HAVE_ARCH_HUGE_VMAP #  arch supports the ioremap_pud_enabled() and ioremap_pmd_enabled() VM APIs
        vm/ ioremap_prot         : VS.  -- |                   HAVE_IOREMAP_PROT #  arch has ioremap_prot()
        vm/ numa-memblock        : VS.  ok |              HAVE_MEMBLOCK_NODE_MAP #  arch supports NUMA aware memblocks
        vm/ PG_uncached          : VS.  -- |               ARCH_USES_PG_UNCACHED #  arch supports the PG_uncached page flag
        vm/ pte_special          : VS.  -- |             __HAVE_ARCH_PTE_SPECIAL #  arch supports the pte_special()/pte_mkspecial() VM APIs
        vm/ THP                  : VS.  -- |      HAVE_ARCH_TRANSPARENT_HUGEPAGE #  arch supports transparent hugepages
        vm/ batch-unmap-tlb-flush: VS.  -- |   ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH #  arch supports deferral of TLB flush until multiple pages are unmapped


Suggesting that riscv is not included within the hard-coded matrices.
This also shows a first limitation of the proposed approach, i.e., it
doesn't parse "Optimized asm/rwsem.h" (wants "true" configs). It also
won't find "__HAVE_ARCH_PTE_SPECIAL" (reads Kconfig files) but things
like "!ARCH_USES_GETTIMEOFFSET" could still be handled...

We could try switching to another architectures: none of these should
result in "core/ BPF-JIT" set: the "HAVE_BPF_JIT" config was splitted
into cBPF and eBPF variants more recently. The comparison of the hard
coded status flags with the new/generated flags should also highlight
out-of-date values.

Alternative/Additional help could probably be provided by checkpatch,
say, warn when a patch touches/adds to Kconfig without updating such
documentation...

Thoughts?

  Andrea
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