Index: sys/boot/efi/loader/arch/amd64/elf64_freebsd.c
===================================================================
--- sys/boot/efi/loader/arch/amd64/elf64_freebsd.c
+++ sys/boot/efi/loader/arch/amd64/elf64_freebsd.c
@@ -101,6 +101,17 @@
 	char			buf[24];
 	int			revision;
 
+	/*
+	 * Report the RSDP to the kernel. While this can be found with
+	 * a BIOS boot, the RSDP may be elsewhere when booted from UEFI.
+	 * The old code used the 'hints' method to communite this to
+	 * the kernel. However, while convenient, the 'hints' method
+	 * is fragile and does not work when static hints are compiled
+	 * into the kernel. Instead, move to setting different tunables
+	 * that start with acpi. The old 'hints' can be removed before
+	 * we branch for FreeBSD 12.
+	 */
+
 	rsdp = efi_get_table(&acpi20_guid);
 	if (rsdp == NULL) {
 		rsdp = efi_get_table(&acpi_guid);
@@ -108,23 +119,29 @@
 	if (rsdp != NULL) {
 		sprintf(buf, "0x%016llx", (unsigned long long)rsdp);
 		setenv("hint.acpi.0.rsdp", buf, 1);
+		setenv("acpi.rsdp", buf, 1);
 		revision = rsdp->Revision;
 		if (revision == 0)
 			revision = 1;
 		sprintf(buf, "%d", revision);
 		setenv("hint.acpi.0.revision", buf, 1);
+		setenv("acpi.revision", buf, 1);
 		strncpy(buf, rsdp->OemId, sizeof(rsdp->OemId));
 		buf[sizeof(rsdp->OemId)] = '\0';
 		setenv("hint.acpi.0.oem", buf, 1);
+		setenv("acpi.oem", buf, 1);
 		sprintf(buf, "0x%016x", rsdp->RsdtPhysicalAddress);
 		setenv("hint.acpi.0.rsdt", buf, 1);
+		setenv("acpi.rsdt", buf, 1);
 		if (revision >= 2) {
 			/* XXX extended checksum? */
 			sprintf(buf, "0x%016llx",
 			    (unsigned long long)rsdp->XsdtPhysicalAddress);
 			setenv("hint.acpi.0.xsdt", buf, 1);
+			setenv("acpi.xsdt", buf, 1);
 			sprintf(buf, "%d", rsdp->Length);
 			setenv("hint.acpi.0.xsdt_length", buf, 1);
+			setenv("acpi.xsdt_length", buf, 1);
 		}
 	}
 
Index: sys/boot/i386/libi386/biosacpi.c
===================================================================
--- sys/boot/i386/libi386/biosacpi.c
+++ sys/boot/i386/libi386/biosacpi.c
@@ -60,25 +60,40 @@
     if ((rsdp = biosacpi_find_rsdp()) == NULL)
 	return;
 
-    /* export values from the RSDP */
+    /*
+     * Report the RSDP to the kernel. While this can be found with
+     * a BIOS boot, the RSDP may be elsewhere when booted from UEFI.
+     * The old code used the 'hints' method to communite this to
+     * the kernel. However, while convenient, the 'hints' method
+     * is fragile and does not work when static hints are compiled
+     * into the kernel. Instead, move to setting different tunables
+     * that start with acpi. The old 'hints' can be removed before
+     * we branch for FreeBSD 12.
+     */
     sprintf(buf, "0x%08x", VTOP(rsdp));
     setenv("hint.acpi.0.rsdp", buf, 1);
+    setenv("acpi.rsdp", buf, 1);
     revision = rsdp->Revision;
     if (revision == 0)
 	revision = 1;
     sprintf(buf, "%d", revision);
     setenv("hint.acpi.0.revision", buf, 1);
+    setenv("acpi.revision", buf, 1);
     strncpy(buf, rsdp->OemId, sizeof(rsdp->OemId));
     buf[sizeof(rsdp->OemId)] = '\0';
     setenv("hint.acpi.0.oem", buf, 1);
+    setenv("acpi.oem", buf, 1);
     sprintf(buf, "0x%08x", rsdp->RsdtPhysicalAddress);
     setenv("hint.acpi.0.rsdt", buf, 1);
+    setenv("acpi.rsdt", buf, 1);
     if (revision >= 2) {
 	/* XXX extended checksum? */
 	sprintf(buf, "0x%016llx", rsdp->XsdtPhysicalAddress);
 	setenv("hint.acpi.0.xsdt", buf, 1);
+	setenv("acpi.xsdt", buf, 1);
 	sprintf(buf, "%d", rsdp->Length);
 	setenv("hint.acpi.0.xsdt_length", buf, 1);
+	setenv("acpi.xsdt_length", buf, 1);
     }
 }
 
Index: sys/x86/acpica/OsdEnvironment.c
===================================================================
--- sys/x86/acpica/OsdEnvironment.c
+++ sys/x86/acpica/OsdEnvironment.c
@@ -30,6 +30,7 @@
 
 #include <sys/types.h>
 #include <sys/bus.h>
+#include <sys/kernel.h>
 #include <sys/sysctl.h>
 
 #include <contrib/dev/acpica/include/acpi.h>
@@ -59,6 +60,16 @@
 {
 	long acpi_root;
 
+	if (TUNABLE_ULONG_FETCH("acpi.rsdp", &acpi_root))
+		return (acpi_root);
+
+	/*
+	 * The hints mechanism is unreliable (it fails if anybody ever
+	 * compiled in hints to the kernel). It has been replaced
+	 * by the tunable method, but is used here as a fallback to
+	 * retain maximum compatibility between old loaders and new
+	 * kernels. It can be removed after 11.0R.
+	 */
 	if (resource_long_value("acpi", 0, "rsdp", &acpi_root) == 0)
 		return (acpi_root);