s390: introduce .boot.preserved.data section

Introduce .boot.preserve.data section which is similar to .boot.data and
"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.

Unlike .boot.data section .boot.preserved.data is NOT a part of init data,
and hence will be preserved for the kernel life time.
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/boot/compressed/decompressor.h

@@ -17,6 +17,8 @@ struct vmlinux_info {
 	unsigned long bss_size;		/* uncompressed image .bss size */
 	unsigned long bootdata_off;
 	unsigned long bootdata_size;
+	unsigned long bootdata_preserved_off;
+	unsigned long bootdata_preserved_size;
 };
 
 extern char _vmlinux_info[];

arch/s390/boot/compressed/vmlinux.lds.S

@@ -34,6 +34,7 @@ SECTIONS
 		_edata = . ;
 	}
 	BOOT_DATA
+	BOOT_DATA_PRESERVED
 
 	/*
 	 * uncompressed image info used by the decompressor it should match

arch/s390/boot/startup.c

@@ -6,6 +6,7 @@
 #include "boot.h"
 
 extern char __boot_data_start[], __boot_data_end[];
+extern char __boot_data_preserved_start[], __boot_data_preserved_end[];
 
 void error(char *x)
 {
@@ -43,6 +44,9 @@ static void copy_bootdata(void)
 	if (__boot_data_end - __boot_data_start != vmlinux.bootdata_size)
 		error(".boot.data section size mismatch");
 	memcpy((void *)vmlinux.bootdata_off, __boot_data_start, vmlinux.bootdata_size);
+	if (__boot_data_preserved_end - __boot_data_preserved_start != vmlinux.bootdata_preserved_size)
+		error(".boot.preserved.data section size mismatch");
+	memcpy((void *)vmlinux.bootdata_preserved_off, __boot_data_preserved_start, vmlinux.bootdata_preserved_size);
 }
 
 void startup_kernel(void)

arch/s390/include/asm/sections.h

@@ -16,4 +16,11 @@
  */
 #define __bootdata(var) __section(.boot.data.var) var
 
+/*
+ * .boot.preserved.data is similar to .boot.data, but it is not part of the
+ * .init section and thus will be preserved for later use in the decompressed
+ * kernel.
+ */
+#define __bootdata_preserved(var) __section(.boot.preserved.data.var) var
+
 #endif

arch/s390/include/asm/vmlinux.lds.h

@@ -18,3 +18,16 @@
 		*(SORT_BY_ALIGNMENT(SORT_BY_NAME(.boot.data*)))		\
 		__boot_data_end = .;					\
 	}
+
+/*
+ * .boot.preserved.data is similar to .boot.data, but it is not part of the
+ * .init section and thus will be preserved for later use in the decompressed
+ * kernel.
+ */
+#define BOOT_DATA_PRESERVED						\
+	. = ALIGN(PAGE_SIZE);						\
+	.boot.preserved.data : {					\
+		__boot_data_preserved_start = .;			\
+		*(SORT_BY_ALIGNMENT(SORT_BY_NAME(.boot.preserved.data*))) \
+		__boot_data_preserved_end = .;				\
+	}

arch/s390/kernel/vmlinux.lds.S

@@ -72,6 +72,7 @@ SECTIONS
 	__end_ro_after_init = .;
 
 	RW_DATA_SECTION(0x100, PAGE_SIZE, THREAD_SIZE)
+	BOOT_DATA_PRESERVED
 
 	_edata = .;		/* End of data section */
 
@@ -161,6 +162,9 @@ SECTIONS
 		QUAD(__bss_stop - __bss_start)			/* bss_size */
 		QUAD(__boot_data_start)				/* bootdata_off */
 		QUAD(__boot_data_end - __boot_data_start)	/* bootdata_size */
+		QUAD(__boot_data_preserved_start)		/* bootdata_preserved_off */
+		QUAD(__boot_data_preserved_end -
+		     __boot_data_preserved_start)		/* bootdata_preserved_size */
 	} :NONE
 
 	/* Debugging sections.	*/