x86/unwind/orc: Remove boot-time ORC unwind tables sorting

Now that the orc_unwind and orc_unwind_ip tables are sorted at build time,
remove the boot time sorting pass.

No change in functionality.

[ mingo: Rewrote the changelog and code comments. ]

Signed-off-by: Shile Zhang <shile.zhang@linux.alibaba.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kbuild@vger.kernel.org
Link: https://lkml.kernel.org/r/20191204004633.88660-8-shile.zhang@linux.alibaba.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/unwind_orc.c

@@ -273,9 +273,11 @@ void __init unwind_init(void)
 		return;
 	}
 
-	/* Sort the .orc_unwind and .orc_unwind_ip tables: */
-	sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_cmp,
-	     orc_sort_swap);
+	/*
+	 * Note, the orc_unwind and orc_unwind_ip tables were already
+	 * sorted at build time via the 'sorttable' tool.
+	 * It's ready for binary search straight away, no need to sort it.
+	 */
 
 	/* Initialize the fast lookup table: */
 	lookup_num_blocks = orc_lookup_end - orc_lookup;

scripts/link-vmlinux.sh

@@ -306,7 +306,10 @@ vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
 
 if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then
 	info SORTTAB vmlinux
-	sorttable vmlinux
+	if ! sorttable vmlinux; then
+		echo >&2 Failed to sort kernel tables
+		exit 1
+	fi
 fi
 
 info SYSMAP System.map