On 8/4/23 08:05, Wilco Dijkstra via Gcc-patches wrote:
+#ifdef HWCAP_USCAT
+
+#define MIDR_IMPLEMENTOR(midr) (((midr) >> 24) & 255)
+#define MIDR_PARTNUM(midr) (((midr) >> 4) & 0xfff)
+
+static inline bool
+ifunc1 (unsigned long hwcap)
+{
+ if (hwcap & HWCAP_USCAT)
+ return true;
+ if (!(hwcap & HWCAP_CPUID))
+ return false;
+
+ unsigned long midr;
+ asm volatile ("mrs %0, midr_el1" : "=r" (midr));
+
+ /* Neoverse N1 supports atomic 128-bit load/store. */
+ if (MIDR_IMPLEMENTOR (midr) == 'A' && MIDR_PARTNUM(midr) == 0xd0c)
+ return true;
+
+ return false;
+}
+#endif
Why would HWCAP_USCAT not be set by the kernel?
Failing that, I would think you would check ID_AA64MMFR2_EL1.AT.
r~
