zipl: do not overwrite BOOT_IMAGE entry

The zipl internal loader adds a variable BOOT_IMAGE= to the commandline
so that it is visible in the operating system which menu entry has been
chosen.

This entry was overwritten by the stage3 parameter page.

Fix by re-arranging the internal memory layout and putting the command
line extra param, which contains the BOOT_IMAGE entry, at 0xe000.
This location is available because less than  one page is used for the
stack.

Fixes: https://github.com/ibm-s390-tools/s390-tools/issues/67
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zipl/boot/Makefile

@@ -6,7 +6,7 @@ CFLAGS_BOOT = $(NO_PIE_CFLAGS) -Os -g -I../include -D__ASSEMBLY__ \
 	  -fno-builtin -ffreestanding -fno-asynchronous-unwind-tables \
 	  -fno-delete-null-pointer-checks \
 	  -fexec-charset=IBM1047 -m64 -mpacked-stack \
-	  -mstack-size=8192 -mstack-guard=128 -msoft-float \
+	  -mstack-size=4096 -mstack-guard=128 -msoft-float \
 	  -W -Wall -Wformat-security
 
 FILES	= fba0.bin fba1b.bin fba2.bin \
@@ -91,7 +91,7 @@ stage3.bin:	stage3.exec
 		--only-section=.stage2dump.tail \
 		--only-section=.eckd2dump_mv.tail \
 		--only-section=.fixup \
-		--pad-to=0xf000 \
+		--pad-to=0xe000 \
 		$< $@
 
 data.o: $(FILES)

zipl/boot/menu.h

@@ -15,7 +15,7 @@
 #include "stage2.h"
 
 /* address of extra command line */
-#define COMMAND_LINE_EXTRA	        (0xA000-0x400)
+#define COMMAND_LINE_EXTRA	        0xE000
 
 /* max command line length */
 #define COMMAND_LINE_SIZE	        896

zipl/boot/stage2.lds

@@ -12,7 +12,8 @@
  * 0x6000-0x8fff	Memory allocation (heap)
  * 0x9000-0x9fff        Memory to load stage3 parameter to
  * 0xa000-0xdfff        Memory to load stage3 to
- * 0xe000-0xffff	Stack
+ * 0xe000-0xe3ff	command line extra
+ * 0xe400-0xffff	Stack
  *
  * Special memory locations
  * ------------------------

zipl/boot/stage3.h

@@ -22,7 +22,7 @@
 #define OLDMEM_SIZE		 0x10420
 #define COMMAND_LINE		 0x10480
 #define COMMAND_LINE_SIZE	 896
-#define COMMAND_LINE_EXTRA	 (0xA000-0x400)
+#define COMMAND_LINE_EXTRA       0xE000
 
 #define STAGE3_FLAG_SCSI	 0x0001000000000000ULL
 #define STAGE3_FLAG_KDUMP	 0x0002000000000000ULL