bsd-user/freebsd/os-syscall.c: Add get_errno and host_to_target_errno

Add the helper functions get_errno and host_to_target_errno. get_errno
returns either the system call results, or the -errno when system call
indicates failure by returning -1. Host_to_target_errno returns errno
(since on FreeBSD they are the same on all architectures) along with a
comment about why it's the identity.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

bsd-user/freebsd/os-syscall.c

@@ -45,9 +45,30 @@ void target_set_brk(abi_ulong new_brk)
 {
 }
 
+/*
+ * errno conversion.
+ */
+abi_long get_errno(abi_long ret)
+{
+    if (ret == -1) {
+        return -host_to_target_errno(errno);
+    } else {
+        return ret;
+    }
+}
+
+int host_to_target_errno(int err)
+{
+    /*
+     * All the BSDs have the property that the error numbers are uniform across
+     * all architectures for a given BSD, though they may vary between different
+     * BSDs.
+     */
+    return err;
+}
+
 bool is_error(abi_long ret)
 {
-
     return (abi_ulong)ret >= (abi_ulong)(-4096);
 }
 

bsd-user/qemu.h

@@ -246,9 +246,10 @@ extern unsigned long target_dflssiz;
 extern unsigned long target_maxssiz;
 extern unsigned long target_sgrowsiz;
 
-/* syscall.c */
+/* os-syscall.c */
 abi_long get_errno(abi_long ret);
 bool is_error(abi_long ret);
+int host_to_target_errno(int err);
 
 /* os-sys.c */
 abi_long do_freebsd_sysarch(void *cpu_env, abi_long arg1, abi_long arg2);