1 files changed, 27 insertions, 0 deletions
diff --git a/src/thread/aarch64/__set_thread_area.c b/src/thread/aarch64/__set_thread_area.c
new file mode 100644
index 00000000..2ec788e8
--- /dev/null
+++ b/src/thread/aarch64/__set_thread_area.c
@@ -0,0 +1,27 @@
+#include <elf.h>
+#include "libc.h"
+
+#define BITRANGE(a,b) (2*(1UL<<(b))-(1UL<<(a)))
+
+int __set_thread_area(void *p)
+{
+	__asm__ __volatile__ ("msr tpidr_el0,%0" : : "r"(p) : "memory");
+
+	/* Mask off hwcap bits for SME and unknown future features. This is
+	 * necessary because SME is not safe to use without libc support for
+	 * it, and we do not (yet) have such support. */
+	for (size_t *v = libc.auxv; *v; v+=2) {
+		if (v[0]==AT_HWCAP) {
+			v[1] &= ~BITRANGE(42,63); /* 42-47 are SME */
+		} else if (v[0]==AT_HWCAP2) {
+			v[1] &= ~(BITRANGE(23,30)
+			        | BITRANGE(37,42)
+			        | BITRANGE(57,62));
+		} else if (v[0]==AT_HWCAP3 || v[0]==AT_HWCAP4) {
+			v[0] = AT_IGNORE;
+			v[1] = 0;
+		}
+	}
+
+	return 0;
+}