[linuxsh-dev] Parameter block with zImage.

[David W. <dw...@in...>]

When we load a zImage, we load it to 0x210000 and it decompresses the real
kernel image to 0x1000.

The parameter block is in the first page of memory, and the zImage
decompression code doesn't touch it. The bootloader is expected to load the
zImage to 0x210000 and the parameters to 0x0.

Does anyone actually pass parameters to the kernel this way? I'd like to 
change the address at which the zImage expects the parameter block to be 
loaded - to load it to the beginning of the zImage just as we would 
normally load it at the beginning of a vmlinux.

The attached patch does this - moves the entry point of the zImage to 
0x211000 and makes it copy the parameter block from 0x210000 to 0 after 
decompressing the kernel image to 0x1000 as before. 

It puts a jmp insn in at 0x210000 for backward compatibility with 
bootloaders which don't look at the entry point of the loaded image. 

This would break parameter passing for anyone who is currently using a 
zImage and passing parameters by putting the param block at the beginning 
of memory. 

Is anyone actually doing that?

Index: arch/sh/boot/compressed/Makefile
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/boot/compressed/Makefile,v
retrieving revision 1.6
diff -u -r1.6 Makefile
--- arch/sh/boot/compressed/Makefile	2000/10/03 00:47:32	1.6
+++ arch/sh/boot/compressed/Makefile	2001/07/04 13:38:43
@@ -19,8 +19,9 @@
 # ZIMAGE_OFFSET is the load offset of the compression loader
 #
 ZIMAGE_OFFSET = $(shell printf "0x%8x" $$[0x80000000+0x$(CONFIG_MEMORY_START)+0x200000+0x10000])
+ZIMAGE_ENTRY = $(shell printf "0x%8x" $$[$(ZIMAGE_OFFSET)+0x1000])
 
-ZLINKFLAGS = -Ttext $(ZIMAGE_OFFSET) $(ZLDFLAGS)
+ZLINKFLAGS = -Ttext $(ZIMAGE_OFFSET) $(ZLDFLAGS) -e $(ZIMAGE_ENTRY)
 
 all: vmlinux
 
Index: arch/sh/boot/compressed/head.S
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/boot/compressed/head.S,v
retrieving revision 1.5
diff -u -r1.5 head.S
--- arch/sh/boot/compressed/head.S	2000/12/24 23:52:56	1.5
+++ arch/sh/boot/compressed/head.S	2001/07/04 13:38:44
@@ -8,7 +8,19 @@
 
 #include <linux/linkage.h>
 
+	.global params
+	
+params:
+	mov.l	startup_addr, r0
+	jmp	@r0
+
+startup_addr:
+	.long	startup
+	
+.org	0x1000
+
 	.global	startup
+
 startup:
 	/* Load initial status register */
 	mov.l   init_sr, r1
Index: arch/sh/boot/compressed/misc.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/boot/compressed/misc.c,v
retrieving revision 1.5
diff -u -r1.5 misc.c
--- arch/sh/boot/compressed/misc.c	2000/07/20 15:55:00	1.5
+++ arch/sh/boot/compressed/misc.c	2001/07/04 13:38:44
@@ -96,6 +96,7 @@
 extern int _end;
 static unsigned long free_mem_ptr;
 static unsigned long free_mem_end_ptr;
+extern int params;
  
 #define HEAP_SIZE             0x10000
 
@@ -224,6 +225,18 @@
 long user_stack [STACK_SIZE];
 long* stack_start = &user_stack[STACK_SIZE];
 
+void copy_param_block(void)
+{
+	int i;
+
+	unsigned long *src = (unsigned long *)&params;
+	unsigned long *dst = (unsigned long *)&_text + 0x20000000;
+
+	for(i=0; i<0x1000/4; i++) {
+		dst[i]=src[i];
+	}
+}
+
 void decompress_kernel(void)
 {
 	output_data = 0;
@@ -231,6 +244,7 @@
 	free_mem_ptr = (unsigned long)&_end;
 	free_mem_end_ptr = free_mem_ptr + HEAP_SIZE;
 
+	copy_param_block();
 	makecrc();
 	puts("Uncompressing Linux... ");
 	gunzip();

--
dwmw2