FROMLIST: kheaders: dereferences the source tree

When the kernel is built inside a sandbox container,
a forest of symlinks to the source files may be
created in the container. In this case, the generated
kheaders.tar.xz should follow these symlinks
to access the source files, instead of packing
the symlinks themselves.

Test: manual (add kheaders_data.tar.xz to the output,
  then examine the contents)
Bug: 276339429
Fixes: b0acbba ("Revert "Revert "Revert "FROMLIST: kheaders: Follow symlinks to source files."""")
Link: https://lore.kernel.org/lkml/[email protected]/
Change-Id: Ie4db22dfa13d05fdccb3ad8f4fae2fe3fead994e
Signed-off-by: Yifan Hong <[email protected]>

Author: Yifan Hong

kernel/gen_kheaders.sh

@@ -73,15 +73,15 @@ if [ "$building_out_of_srctree" ]; then
 		cd $srctree
 		for f in $dir_list
 			do find "$f" -name "*.h";
-		done | cpio --quiet -pd $cpio_dir
+		done | cpio --quiet -L -pd $cpio_dir
 	)
 fi
 
 # The second CPIO can complain if files already exist which can happen with out
 # of tree builds having stale headers in srctree. Just silence CPIO for now.
 for f in $dir_list;
 	do find "$f" -name "*.h";
-done | cpio --quiet -pdu $cpio_dir >/dev/null 2>&1
+done | cpio --quiet -L -pdu $cpio_dir >/dev/null 2>&1
 
 # Remove comments except SDPX lines
 find $cpio_dir -type f -print0 |