Re: [linuxsh-dev] How to use an initrd?

[Alessandro R. <ru...@gn...>]

>> That should work. If you or someone else is interested in my
>> implementation, I'll post the real code and script tomorrow.
> 
> Yes, please.

Ok. This morning I managed to populate my ramdisk and boot, it works
fine, however the SCIF interrupts are not registered so I can't send
input to my shell (I only see SCI in /proc/interrupts). This is because
I use SCIF as console, and is independent of the ramdisk problem.

  BTW: can someone please point me to a libc suited for cross-compiling?
  Building one is tedious, and with the available packages I only managed
  to compile with horrible -I and -L arguments to the target, but
  only statical linking was possible. Thanks.

Like you, I have no full-featured boot loader, yet. I boot via an eprom
tailoerd for vxworks and I can only load a single ELF file from disk.

At the end you find the short patch that I used to make initrd work. To
convert the ramdisk to object file, use this Makefile:

    all: ramdisk.o
	    cp $^ linux/arch/sh/boot
    
    ramdisk.o: ramdisk.gz
	    sh4eb-linux-ld -r -T ramdisk.lds -b binary \
		      -o $@ $^
    
    ramdisk.gz: ramdisk
	    gzip < $^ > $@

ramdisk.lds is here:

    OUTPUT_FORMAT("elf32-shbig-linuxs")
    OUTPUT_ARCH(sh)
    SECTIONS
    {
      .data :
      {
	     __rd_start = .;
	     *(.data)
	     __rd_end = .;
      }
    }

The patch does what I described last time, plus it disables freeing
the ramdisk because it isn't aligned (I know it can be aligned
somehow, I just didn't go further on that path), so such freeing
released valuable memory as well and the kernel locked hard right
after mounting the fs; most likely because some allocation overwritten
valuable data.  Please note that the patch uses a new CONFIG option
for the platform we are using.

It's pretty dirty stuff, but it works fine to boot with a single file
if you can't do anything else.

--- ./arch/sh/kernel/Makefile.orig	Thu Nov 22 02:04:17 2001
+++ ./arch/sh/kernel/Makefile	Thu Nov 22 02:05:07 2001
@@ -23,6 +23,8 @@
 obj-$(CONFIG_SH_RTC)            += rtc.o
 obj-$(CONFIG_SH_DMA)		+= dma.o
 obj-$(CONFIG_SH_STANDARD_BIOS)	+= sh_bios.o
+obj-$(CONFIG_BLK_DEV_INITRD)    += ../boot/ramdisk.o
+
 
 ifeq ($(CONFIG_PCI),y)
 ifeq ($(CONFIG_SH_DREAMCAST),y)
--- ./arch/sh/kernel/setup.c.orig	Thu Nov 22 02:08:16 2001
+++ ./arch/sh/kernel/setup.c	Thu Nov 22 02:18:05 2001
@@ -438,6 +438,15 @@
 	reserve_bootmem_node(NODE_DATA(0), __MEMORY_START, PAGE_SIZE);
 
 #ifdef CONFIG_BLK_DEV_INITRD
+#ifdef CONFIG_SH_GX8TSU
+	{
+        extern void * __rd_start, * __rd_end;
+
+        initrd_start = (unsigned long)&__rd_start;
+        initrd_end = (unsigned long)&__rd_end;
+        initrd_below_start_ok = 1;
+	}
+#else
 	if (LOADER_TYPE && INITRD_START) {
 		if (INITRD_START + INITRD_SIZE <= (max_low_pfn << PAGE_SHIFT)) {
 			reserve_bootmem_node(NODE_DATA(0), INITRD_START+__MEMORY_START, INITRD_SIZE);
@@ -452,6 +461,7 @@
 			initrd_start = 0;
 		}
 	}
+#endif /* GX8TSU */
 #endif
 
 #if 0
--- ./arch/sh/mm/init.c.orig	Thu Nov 22 16:04:36 2001
+++ ./arch/sh/mm/init.c	Thu Nov 22 16:05:32 2001
@@ -193,6 +193,7 @@
 #ifdef CONFIG_BLK_DEV_INITRD
 void free_initrd_mem(unsigned long start, unsigned long end)
 {
+#if 0 /* GX8 tmp hack */
 	unsigned long p;
 	for (p = start; p < end; p += PAGE_SIZE) {
 		ClearPageReserved(virt_to_page(p));
@@ -201,6 +202,7 @@
 		totalram_pages++;
 	}
 	printk ("Freeing initrd memory: %ldk freed\n", (end - start) >> 10);
+#endif
 }
 #endif