On Thu, May 13, 2021 at 10:35:04AM +0530, Anshuman Khandual wrote:

On 4/28/21 5:42 PM, Mark Brown wrote:

quoted

The arm64 code allocates an internal constant to every CPU feature it can
detect, distinct from the public hwcap numbers we use to expose some
features to userspace. Currently this is maintained manually which is an
irritating source of conflicts when working on new features, to avoid this
replace the header with a simple text file listing the names we've assigned
and sort it to minimise conflicts.

As part of doing this we also do the Kbuild hookup required to hook up
an arch tools directory and to generate header files in there.

This will result in a renumbering and reordering of the existing constants,
since they are all internal only the values should not be important. The
reordering will impact the order in which some steps in enumeration handle
features but the algorithm is not intended to depend on this and I haven't
seen any issues when testing. Due to the UAO cpucap having been removed in
the past we end up with ARM64_NCAPS being 1 smaller than it was before.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/Makefile              |  3 ++
 arch/arm64/include/asm/Kbuild    |  2 +
 arch/arm64/include/asm/cpucaps.h | 74 --------------------------------
 arch/arm64/tools/Makefile        | 22 ++++++++++
 arch/arm64/tools/cpucaps         | 65 ++++++++++++++++++++++++++++
 arch/arm64/tools/gen-cpucaps.awk | 40 +++++++++++++++++
 6 files changed, 132 insertions(+), 74 deletions(-)
 delete mode 100644 arch/arm64/include/asm/cpucaps.h
 create mode 100644 arch/arm64/tools/Makefile
 create mode 100644 arch/arm64/tools/cpucaps
 create mode 100755 arch/arm64/tools/gen-cpucaps.awk

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 7ef44478560d..b52481f0605d 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile

@@ -175,6 +175,9 @@ vdso_install:
 	$(if $(CONFIG_COMPAT_VDSO), \
 		$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 $@)
 
+archprepare:
+	$(Q)$(MAKE) $(build)=arch/arm64/tools kapi

Small nit. So going forward this new directory (arch/arm64/tools/), will
be used to hold similar scripts that generate header or similar things ?
At first the directory name 'tool' was bit confusing but seems like other
archs (arm, m68k, mips, powerpc, s390, sh) have this directory as well.

Yup; there's more stuff we might want to put here in future, e.g.

* Generation of (or consistency-checks) for the kernel HWCAP glue
* Generation of the sysreg headers
* Generation of the insn code
* Generation of metadata (or consistency checks) for
  RELIABLE_STACKTRACE, LIVEPATCH, etc

[...]

quoted

+BEGIN {
+	print "#ifndef __ASM_CPUCAPS_H"
+	print "#define __ASM_CPUCAPS_H"
+	print ""
+	print "/* Generated file - do not edit */"
+	cap_num = 0
+	print ""
+}
+
+/^[vA-Z0-9_]+$/ {

Small nit. Should this be length restricted at the least ?
Like each CAP entries should not exceed a certain length.

I don't think we should enforce a length limit in the script, as we'd
have to select an arbitrary limit, and given we should catch exceedingly
long names during review, I think it's more likely to be a hindrance
than a help (e.g. if we ever bump up against that limit).

quoted

+	printf("#define ARM64_%-30s\t%d\n", $0, cap_num++)
+	next
+}
+
+END {
+	printf("#define ARM64_NCAPS\t\t\t\t%d\n", cap_num)
+	print ""
+	print "#endif"

Small nit. Should it be print "#endif /* __ASM_CPUCAPS_H */" instead
in order to be complete.

Agreed; that would be nice.

Thanks,
Mark.

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