s390: introduce .boot.data section

Introduce .boot.data section which is "shared" between the decompressor
code and the decompressed kernel. The decompressor will store values in
it, and copy over to the decompressed image before starting it. This
method allows to avoid using pre-defined addresses and other hacks to
pass values between those boot phases.

.boot.data section is a part of init data, and will be freed after kernel
initialization is complete.

For uncompressed kernel image, .boot.data section is basically the same
as .init.data

Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 32 insertions, 0 deletions

diff --git a/arch/s390/include/asm/sections.h b/arch/s390/include/asm/sections.h
index 724faede8ac5..7afe4620685c 100644
--- a/arch/s390/include/asm/sections.h
+++ b/arch/s390/include/asm/sections.h
@@ -4,4 +4,16 @@
 
 #include <asm-generic/sections.h>
 
+/*
+ * .boot.data section contains variables "shared" between the decompressor and
+ * the decompressed kernel. The decompressor will store values in them, and
+ * copy over to the decompressed image before starting it.
+ *
+ * Each variable end up in its own intermediate section .boot.data.<var name>,
+ * those sections are later sorted by alignment + name and merged together into
+ * final .boot.data section, which should be identical in the decompressor and
+ * the decompressed kernel (that is checked during the build).
+ */
+#define __bootdata(var) __section(.boot.data.var) var
+
 #endif
diff --git a/arch/s390/include/asm/vmlinux.lds.h b/arch/s390/include/asm/vmlinux.lds.h
new file mode 100644
index 000000000000..2d127f900352
--- /dev/null
+++ b/arch/s390/include/asm/vmlinux.lds.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm/page.h>
+
+/*
+ * .boot.data section is shared between the decompressor code and the
+ * decompressed kernel. The decompressor will store values in it, and copy
+ * over to the decompressed image before starting it.
+ *
+ * .boot.data variables are kept in separate .boot.data.<var name> sections,
+ * which are sorted by alignment first, then by name before being merged
+ * into single .boot.data section. This way big holes cased by page aligned
+ * structs are avoided and linker produces consistent result.
+ */
+#define BOOT_DATA							\
+	. = ALIGN(PAGE_SIZE);						\
+	.boot.data : {							\
+		__boot_data_start = .;					\
+		*(SORT_BY_ALIGNMENT(SORT_BY_NAME(.boot.data*)))		\
+		__boot_data_end = .;					\
+	}