common-user: Initialize mmap_min_addr for FreeBSD

Use sysctl to fetch the vm layout of the current process.

Reviewed-by: Helge Deller <deller@gmx.de>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

common-user/mmap-min-addr.c

@@ -5,6 +5,10 @@
 
 #include "qemu/osdep.h"
 #include "user/mmap-min-addr.h"
+#ifdef __FreeBSD__
+#include <sys/sysctl.h>
+#include <sys/user.h>
+#endif
 
 uintptr_t mmap_min_addr;
 
@@ -31,6 +35,15 @@ static void __attribute__((constructor)) init(void)
         fclose(fp);
     }
     mmap_min_addr = min_addr;
+#elif defined(__FreeBSD__)
+    int mib[] = { CTL_KERN, KERN_PROC, KERN_PROC_VM_LAYOUT, getpid() };
+    struct kinfo_vm_layout info;
+    size_t info_len = sizeof(info);
+
+    mmap_min_addr =
+        (sysctl(mib, ARRAY_SIZE(mib), &info, &info_len, NULL, 0) < 0
+         ? qemu_real_host_page_size()
+         : info.kvm_min_user_addr);
 #else
 # error
 #endif