arm64: extable: sort the exception table at build time

As is done for other architectures, sort the exception table at
build-time rather than during boot.

Since sortextable appears to be a standalone C program relying on the
host elf.h to provide EM_AARCH64, I've had to add a conditional check in
order to allow cross-compilation on machines that aren't running a
bleeding-edge libc-dev.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -7,6 +7,7 @@ config ARM64
 	select ARM_AMBA
 	select ARM_ARCH_TIMER
 	select ARM_GIC
+	select BUILDTIME_EXTABLE_SORT
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select GENERIC_CLOCKEVENTS

arch/arm64/kernel/vmlinux.lds.S

@@ -56,7 +56,7 @@ SECTIONS
 	}
 
 	RO_DATA(PAGE_SIZE)
-
+	EXCEPTION_TABLE(8)
 	_etext = .;			/* End of text and rodata section */
 
 	. = ALIGN(PAGE_SIZE);
@@ -98,14 +98,6 @@ SECTIONS
 		CACHELINE_ALIGNED_DATA(64)
 		READ_MOSTLY_DATA(64)
 
-		/*
-		 * The exception fixup table (might need resorting at runtime)
-		 */
-		. = ALIGN(32);
-		__start___ex_table = .;
-		*(__ex_table)
-		__stop___ex_table = .;
-
 		/*
 		 * and the usual data section
 		 */

scripts/sortextable.c

@@ -31,6 +31,10 @@
 #include <tools/be_byteshift.h>
 #include <tools/le_byteshift.h>
 
+#ifndef EM_AARCH64
+#define EM_AARCH64	183
+#endif
+
 static int fd_map;	/* File descriptor for file being modified. */
 static int mmap_failed; /* Boolean flag. */
 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
@@ -249,6 +253,7 @@ do_file(char const *const fname)
 		custom_sort = sort_relative_table;
 		break;
 	case EM_ARM:
+	case EM_AARCH64:
 	case EM_MIPS:
 		break;
 	}  /* end switch */