Add a "fork" of musl as //fusl.

fusl/arch/arm/src/__set_thread_area.c

Index: fusl/arch/arm/src/__set_thread_area.c
diff --git a/fusl/arch/arm/src/__set_thread_area.c b/fusl/arch/arm/src/__set_thread_area.c
new file mode 100644
index 0000000000000000000000000000000000000000..61d02827b5c1420c197fe287b99aac4e237e80b9
--- /dev/null
+++ b/fusl/arch/arm/src/__set_thread_area.c
@@ -0,0 +1,49 @@
+#include <stdint.h>
+#include <elf.h>
+#include "pthread_impl.h"
+#include "libc.h"
+
+#define HWCAP_TLS (1 << 15)
+
+extern const unsigned char __attribute__((__visibility__("hidden")))
+	__a_barrier_dummy[], __a_barrier_oldkuser[],
+	__a_barrier_v6[], __a_barrier_v7[],
+	__a_cas_dummy[], __a_cas_v6[], __a_cas_v7[],
+	__a_gettp_dummy[];
+
+#define __a_barrier_kuser 0xffff0fa0
+#define __a_cas_kuser 0xffff0fc0
+#define __a_gettp_kuser 0xffff0fe0
+
+extern uintptr_t __attribute__((__visibility__("hidden")))
+	__a_barrier_ptr, __a_cas_ptr, __a_gettp_ptr;
+
+#define SET(op,ver) (__a_##op##_ptr = \
+	(uintptr_t)__a_##op##_##ver - (uintptr_t)__a_##op##_dummy)
+
+int __set_thread_area(void *p)
+{
+#if !__ARM_ARCH_7A__ && !__ARM_ARCH_7R__ && __ARM_ARCH < 7
+	if (__hwcap & HWCAP_TLS) {
+		size_t *aux;
+		SET(cas, v7);
+		SET(barrier, v7);
+		for (aux=libc.auxv; *aux; aux+=2) {
+			if (*aux != AT_PLATFORM) continue;
+			const char *s = (void *)aux[1];
+			if (s[0]!='v' || s[1]!='6' || s[2]-'0'<10u) break;
+			SET(cas, v6);
+			SET(barrier, v6);
+			break;
+		}
+	} else {
+		int ver = *(int *)0xffff0ffc;
+		SET(gettp, kuser);
+		SET(cas, kuser);
+		SET(barrier, kuser);
+		if (ver < 2) a_crash();
+		if (ver < 3) SET(barrier, oldkuser);
+	}
+#endif
+	return __syscall(0xf0005, p);
+}