Add CPU feature checks on M1 macOS.

I booted my M1 Mac into macOS rather than Asahi for the first time in
a while, and discovered that an OS update seems to have added some
sysctl flags indicating the presence of the CPU extensions that I
previously knew of no way to check for! Added them checks to
arm_arch_queries.c, though I've also retained backwards compat with
the previous OS version which didn't have them at all.

2 files changed, 27 insertions, 13 deletions

diff --git a/unix/utils/arm_arch_queries.c b/unix/utils/arm_arch_queries.c
index cc3e4125..d6dc97bc 100644
--- a/unix/utils/arm_arch_queries.c
+++ b/unix/utils/arm_arch_queries.c
@@ -17,10 +17,11 @@ bool platform_aes_neon_available(void)
 #elif defined HWCAP2_AES
     return getauxval(AT_HWCAP2) & HWCAP2_AES;
 #elif defined __APPLE__
-    /* M1 macOS defines no optional sysctl flag indicating presence of
-     * the AES extension, which I assume to be because it's always
-     * present */
-    return true;
+    SysctlResult res = test_sysctl_flag("hw.optional.arm.FEAT_AES");
+    /* Older M1 macOS didn't provide this flag, but as far as I know
+     * implemented the crypto extension anyway, so treat 'feature
+     * missing' as 'implemented' */
+    return res != SYSCTL_OFF;
 #else
     return false;
 #endif
@@ -33,8 +34,9 @@ bool platform_sha256_neon_available(void)
 #elif defined HWCAP2_SHA2
     return getauxval(AT_HWCAP2) & HWCAP2_SHA2;
 #elif defined __APPLE__
-    /* Assume always present on M1 macOS, similarly to AES */
-    return true;
+    SysctlResult res = test_sysctl_flag("hw.optional.arm.FEAT_SHA256");
+    /* As above, treat 'missing' as enabled */
+    return res != SYSCTL_OFF;
 #else
     return false;
 #endif
@@ -47,8 +49,9 @@ bool platform_sha1_neon_available(void)
 #elif defined HWCAP2_SHA1
     return getauxval(AT_HWCAP2) & HWCAP2_SHA1;
 #elif defined __APPLE__
-    /* Assume always present on M1 macOS, similarly to AES */
-    return true;
+    SysctlResult res = test_sysctl_flag("hw.optional.arm.FEAT_SHA1");
+    /* As above, treat 'missing' as enabled */
+    return res != SYSCTL_OFF;
 #else
     return false;
 #endif
@@ -61,7 +64,14 @@ bool platform_sha512_neon_available(void)
 #elif defined HWCAP2_SHA512
     return getauxval(AT_HWCAP2) & HWCAP2_SHA512;
 #elif defined __APPLE__
-    return test_sysctl_flag("hw.optional.armv8_2_sha512");
+    /* There are two sysctl flags for this, apparently invented at
+     * different times. Try both, falling back to the older one. */
+    SysctlResult res = test_sysctl_flag("hw.optional.arm.FEAT_SHA512");
+    if (res != SYSCTL_MISSING)
+        return res == SYSCTL_ON;
+
+    res = test_sysctl_flag("hw.optional.armv8_2_sha512");
+    return res == SYSCTL_ON;
 #else
     return false;
 #endif
diff --git a/unix/utils/arm_arch_queries.h b/unix/utils/arm_arch_queries.h
index bd055687..fa46c622 100644
--- a/unix/utils/arm_arch_queries.h
+++ b/unix/utils/arm_arch_queries.h
@@ -49,15 +49,19 @@ static inline u_long getauxval(int which) { return 0; }
 #endif /* defined __arm__ || defined __aarch64__ */
 
 #if defined __APPLE__
-static inline bool test_sysctl_flag(const char *flagname)
+typedef enum { SYSCTL_MISSING, SYSCTL_OFF, SYSCTL_ON } SysctlResult;
+
+static inline SysctlResult test_sysctl_flag(const char *flagname)
 {
 #if HAVE_SYSCTLBYNAME
     int value;
     size_t size = sizeof(value);
-    return (sysctlbyname(flagname, &value, &size, NULL, 0) == 0 &&
-            size == sizeof(value) && value != 0);
+    if (sysctlbyname(flagname, &value, &size, NULL, 0) == 0 &&
+        size == sizeof(value)) {
+        return value != 0 ? SYSCTL_ON : SYSCTL_OFF;
+    }
 #else /* HAVE_SYSCTLBYNAME */
-    return false;
+    return SYSCTL_MISSING;
 #endif /* HAVE_SYSCTLBYNAME */
 }
 #endif /* defined __APPLE__ */