Re: [PATCH] arm64: cpufeature: fix unused function warning

Will Deacon
2020-12-08T10:04:07Z

On Mon, Dec 07, 2020 at 06:19:31PM +0000, Catalin Marinas wrote:
> On Fri, Dec 04, 2020 at 09:59:10AM +0000, Will Deacon wrote:
> > On Thu, Dec 03, 2020 at 11:32:11PM +0100, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@arndb.de>
> > >
> > > The __system_matches_cap() function is now only used in an #ifdef
> > > section:
> > >
> > > arch/arm64/kernel/cpufeature.c:2649:13: error: unused function '__system_matches_cap' [-Werror,-Wunused-function]
> > >
> > > Move it into that #ifdef section.
> > >
> > > Fixes: 7cf283c7bd62 ("arm64: uaccess: remove redundant PAN toggling")
> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> I already queued a fix from Mark: 701f49065e68 ("arm64: mark
> __system_matches_cap as __maybe_unused").
>
> > Acked-by: Will Deacon <will@kernel.org>
> >
> > We can probably go further and remove the helper altogether as I don't
> > think it really helps has_generic_auth(), but this should fix the warning.
>
> We could replace the ARM64_HAS_GENERIC_AUTH checks with a single helper
> function that tests for ARM64_HAS_GENERIC_AUTH_ARCH or
> ARM64_HAS_GENERIC_AUTH_IMP_DEF. Or you had a different idea?

I was just thinking something like below, although it's a bit annoying
that we can't use cpucap_multi_entry_cap_matches() here afaict.

Will

--->8

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 39138f6d3ba2..32a138ce0a92 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -155,8 +155,6 @@ EXPORT_SYMBOL(cpu_hwcap_keys);

static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);

-static bool __system_matches_cap(unsigned int n);
-
/*
* NOTE: Any changes to the visibility of features should be kept in
* sync with the documentation of the CPU feature register ABI.
@@ -1652,8 +1650,13 @@ static bool has_address_auth_metacap(const struct arm64_cpu_capabilities *entry,
static bool has_generic_auth(const struct arm64_cpu_capabilities *entry,
int __unused)
{
- return __system_matches_cap(ARM64_HAS_GENERIC_AUTH_ARCH) ||
- __system_matches_cap(ARM64_HAS_GENERIC_AUTH_IMP_DEF);
+ const struct arm64_cpu_capabilities *cap_arch, *cap_impdef;
+
+ cap_arch = cpu_hwcaps_ptrs[ARM64_HAS_GENERIC_AUTH_ARCH];
+ cap_impdef = cpu_hwcaps_ptrs[ARM64_HAS_GENERIC_AUTH_IMP_DEF];
+
+ return cap_arch->matches(cap_arch, SCOPE_SYSTEM) ||
+ cap_impdef->matches(cap_impdef, SCOPE_SYSTEM);
}
#endif /* CONFIG_ARM64_PTR_AUTH */

@@ -2637,23 +2640,6 @@ bool this_cpu_has_cap(unsigned int n)
return false;
}

-/*
- * This helper function is used in a narrow window when,
- * - The system wide safe registers are set with all the SMP CPUs and,
- * - The SYSTEM_FEATURE cpu_hwcaps may not have been set.
- * In all other cases cpus_have_{const_}cap() should be used.
- */
-static bool __maybe_unused __system_matches_cap(unsigned int n)
-{
- if (n < ARM64_NCAPS) {
- const struct arm64_cpu_capabilities *cap = cpu_hwcaps_ptrs[n];
-
- if (cap)
- return cap->matches(cap, SCOPE_SYSTEM);
- }
- return false;
-}
-
void cpu_set_feature(unsigned int num)
{