add riscv64 architecture support

Author: Alex Suykov <alex.suykov@gmail.com>
Author: Aric Belsito <lluixhi@gmail.com>
Author: Drew DeVault <sir@cmpwn.com>
Author: Michael Clark <mjc@sifive.com>
Author: Michael Forney <mforney@mforney.org>
Author: Stefan O'Rear <sorear2@gmail.com>

This port has involved the work of many people over several years. I
have tried to ensure that everyone with substantial contributions has
been credited above; if any omissions are found they will be noted
later in an update to the authors/contributors list in the COPYRIGHT
file.

The version committed here comes from the riscv/riscv-musl repo's
commit 3fe7e2c75df78eef42dcdc352a55757729f451e2, with minor changes by
me for issues found during final review:

- a_ll/a_sc atomics are removed (according to the ISA spec, lr/sc
  are not safe to use in separate inline asm fragments)

- a_cas[_p] is fixed to be a memory barrier

- the call from the _start assembly into the C part of crt1/ldso is
  changed to allow for the possibility that the linker does not place
  them nearby each other.

- DTP_OFFSET is defined correctly so that local-dynamic TLS works

- reloc.h LDSO_ARCH logic is simplified and made explicit.

- unused, non-functional crti/n asm files are removed.

- an empty .sdata section is added to crt1 so that the
  __global_pointer reference is resolvable.

- indentation style errors in some asm files are fixed.

1 files changed, 33 insertions, 0 deletions

diff --git a/src/linux/cache.c b/src/linux/cache.c
index 84a138a4..0eb051c2 100644
--- a/src/linux/cache.c
+++ b/src/linux/cache.c
@@ -1,4 +1,6 @@
+#include <errno.h>
 #include "syscall.h"
+#include "atomic.h"
 
 #ifdef SYS_cacheflush
 int _flush_cache(void *addr, int len, int op)
@@ -15,3 +17,34 @@ int __cachectl(void *addr, int len, int op)
 }
 weak_alias(__cachectl, cachectl);
 #endif
+
+#ifdef SYS_riscv_flush_icache
+
+#define VDSO_FLUSH_ICACHE_SYM "__vdso_flush_icache"
+#define VDSO_FLUSH_ICACHE_VER "LINUX_4.5"
+
+static void *volatile vdso_func;
+
+static int flush_icache_init(void *start, void *end, unsigned long int flags)
+{
+	void *p = __vdsosym(VDSO_FLUSH_ICACHE_VER, VDSO_FLUSH_ICACHE_SYM);
+	int (*f)(void *, void *, unsigned long int) =
+		(int (*)(void *, void *, unsigned long int))p;
+	a_cas_p(&vdso_func, (void *)flush_icache_init, p);
+	return f ? f(start, end, flags) : -ENOSYS;
+}
+
+static void *volatile vdso_func = (void *)flush_icache_init;
+
+int __riscv_flush_icache(void *start, void *end, unsigned long int flags) 
+{
+	int (*f)(void *, void *, unsigned long int) =
+		(int (*)(void *, void *, unsigned long int))vdso_func;
+	if (f) {
+		int r = f(start, end, flags);
+		if (!r) return r;
+		if (r != -ENOSYS) return __syscall_ret(r);
+	}
+}
+weak_alias(__riscv_flush_icache, riscv_flush_icache);
+#endif