About the decompression of compressed kernel image
From: Zhan Rongkai
Date: Fri Aug 13 2004 - 09:58:00 EST
Hi, everyone:
I am porting linux-2.6.4 to a new architecture
processor. And i have created a compressed kernel
image. Here is my creation steps:
- Use objcopy to translate the 'linux/vmlinux' to
'arch/$(ARCH)/boot/compressed/vmlinux.bin'
- Use 'gzip -f -9' to compress
'arch/$(ARCH)/boot/compressed/vmlinux.bin' to
'arch/$(ARCH)/boot/compressed/vmlinux.bin.gz'
NOTE: The two commands: "gzip -f -9
arch/$(ARCH)/boot/compressed/vmlinux.bin' and
'gzip -f -9 <
arch/$(ARCH)/boot/compressed/vmlinux.bin >
arch/$(ARCH)/boot/compressed/vmlinux.bin.gz' ouput two
copies of
'vmlinux.bin.gz' with different file size. Is it
ok? Why?
- Use the command 'ld -r -b binary' to generate
'arch/$(ARCH)/boot/compressed/piggy.o' from
'arch/$(ARCH)/boot/compressed/vmlinux.bin.gz'
- Then I link the three object files
'compressed/head.o compressed/misc.o
compressed/piggy.o' together, and i get the compressed
kernel image -
'arch/$(ARCH)/boot/compressed/vmlinux'.
- At last, i use objcopy to translate
'arch/$(ARCH)/boot/compressed/vmlinux' to
'arch/$(ARCH)/boot/zImage'
The head.S mainly does four jobs: clear bss section,
setup stack, call decompress_kernel() funcion and jump
to the entry point of
the decompressed kernel image. It has no problems.
When I download the 'zImage' into the target board,
and execute it (bootloader is ok). It print the
following messages:
-------------------------------------------------------------------------------------
Uncompressing
Linux.....................................................................................................................................
inbuf: 0x0000BA44
insize: 0x000724BF
inptr: 0x000724BF
output_ptr: 0x00410000
bytes_out: 0x00410000
ran out of input data
-- System halted
-------------------------------------------------------------------------------------
The following is the result of objdump to the
'arch/$(ARCH)/boot/compressed/vmlinux':
---------------------------------------------
0007df03 g .text 00000000 input_data_end
0000ba44 g .text 00000000 input_data
0000ba40 g .text 00000000 input_len
---------------------------------------------
The file size of the
'arch/$(ARCH)/boot/compressed/vmlinux.bin.gz' is
468159 bytes:
-------------------------------------------------------------------
-rwxr-xr-x 1 root root 468159 8 13 16:24
vmlinux.bin.gz
-------------------------------------------------------------------
So, &input_data_end[0] - &input_data[0] = 0x0007df03 -
0000ba44 = 468159. It is right!
The error message "ran out of input data" is due to
call to the function fill_inbuf(), which is defined in
misc.c file.
When things should be over, why gunzip() still calls
get_byte() ???
The following are the contents of the linker script
template file and misc.c source file:
--------------------------------------------------------------------
SECTIONS
{
. = ZTEXTADDR;
.text : {
_stext = .;
*(.start)
*(.text)
*(.fixup)
*(.gnu.warning)
*(.rodata)
*(.rodata.*)
. = ALIGN(8);
input_len = .;
LONG(input_data_end - input_data)
input_data = .;
arch/$(ARCH)/boot/compressed/piggy.o(.data)
input_data_end = .;
. = ALIGN(4);
}
_etext = .;
.data : { *(.data) }
.got : { *(.got) *(.got.plt) }
_edata = .;
__bss_start = .;
.bss : { *(.bss) }
_end = .;
}
--------------------------------------------------------------------
misc.c:
--------------------------------------------------------------------
#include <linux/config.h>
#include <asm/uaccess.h>
#include "./puts.c"
#define ZDEBUG
#ifdef ZDEBUG
#include "./vsprintf.c"
#endif
/*
* Why do we do this? Don't ask me..
*
* Incomprehensible are the ways of bootloaders.
*/
void* memset(void* s, int c, size_t n)
{
int i;
char *ss = (char*)s;
for (i=0; i<n; i++)
ss[i] = c;
return s;
}
void* memcpy(void* __dest, __const void* __src, size_t
__n)
{
int i;
char *d = (char *)__dest, *s = (char *)__src;
for (i=0; i<__n; i++)
d[i] = s[i];
return __dest;
}
#define memzero(s, n) memset((s), 0, (n))
/*
* gzip delarations
*/
#define OF(args) args
#define STATIC static
typedef unsigned char uch;
typedef unsigned short ush;
typedef unsigned long ulg;
#define WSIZE 0x8000 /* Window size must be at least
32k, */
/* and a power of two */
static uch *inbuf; /* input buffer */
static uch window[WSIZE]; /* Sliding window buffer */
static unsigned insize = 0; /* valid bytes in inbuf */
static unsigned inptr = 0; /* index of next byte to be
processed in inbuf */
static unsigned outcnt = 0; /* bytes in output buffer
*/
/* gzip flag byte */
#define ASCII_FLAG 0x01 /* bit 0 set: file probably
ascii text */
#define CONTINUATION 0x02 /* bit 1 set: continuation
of multi-part gzip file */
#define EXTRA_FIELD 0x04 /* bit 2 set: extra field
present */
#define ORIG_NAME 0x08 /* bit 3 set: original file
name present */
#define COMMENT 0x10 /* bit 4 set: file comment
present */
#define ENCRYPTED 0x20 /* bit 5 set: file is
encrypted */
#define RESERVED 0xC0 /* bit 6,7: reserved */
#define get_byte() (inptr < insize ? inbuf[inptr++] :
fill_inbuf())
/* Diagnostic functions */
#ifdef DEBUG
# define Assert(cond,msg) {if(!(cond)) error(msg);}
# define Trace(x) fprintf x
# define Tracev(x) {if (verbose) fprintf x ;}
# define Tracevv(x) {if (verbose>1) fprintf x ;}
# define Tracec(c,x) {if (verbose && (c)) fprintf x
;}
# define Tracecv(c,x) {if (verbose>1 && (c)) fprintf
x ;}
#else
# define Assert(cond,msg)
# define Trace(x)
# define Tracev(x)
# define Tracevv(x)
# define Tracec(c,x)
# define Tracecv(c,x)
#endif
static int fill_inbuf(void);
static void flush_window(void);
static void error(char *m);
static void gzip_mark(void **);
static void gzip_release(void **);
/* They are defined in the linker script file
'vmlinux.lds.in' */
extern char input_data[];
extern int input_len;
extern char input_data_end[];
static unsigned long bytes_out = 0;
static uch *output_data;
static unsigned long output_ptr = 0;
static void *malloc(int size);
static void free(void *where);
static void error(char *m);
static void gzip_mark(void **);
static void gzip_release(void **);
/* The variable '_end' is defined in the linker script
file
* linux/arch/frvnommu/boot/compressed/vmlinux.lds.in
*/
extern int _end;
static ulg free_mem_ptr;
static ulg free_mem_end_ptr;
#define HEAP_SIZE 0x10000
#include "../../../../lib/inflate.c"
static void *malloc(int size)
{
void *p;
if (size <0) error("Malloc error");
if (free_mem_ptr <= 0) error("Memory error");
free_mem_ptr = (free_mem_ptr + 3) & ~3; /* Align */
p = (void *)free_mem_ptr;
free_mem_ptr += size;
if (free_mem_ptr >= free_mem_end_ptr)
error("Out of memory");
return p;
}
static void free(void *where)
{
/* Don't care: gzip_mark & gzip_release do the free
*/
}
static void gzip_mark(void **ptr)
{
*ptr = (void *) free_mem_ptr;
}
static void gzip_release(void **ptr)
{
free_mem_ptr = (long) *ptr;
}
/*
===========================================================================
* Fill the input buffer. This is called only when the
buffer is empty
* and at least one byte is really needed.
*/
int fill_inbuf(void)
{
if (insize != 0) {
printf("\ninbuf: 0x%.8lX\n", (unsigned long)inbuf);
printf("insize: 0x%.8lX\n", (unsigned long)insize);
printf("inptr: 0x%.8lX\n", (unsigned long)inptr);
printf("output_ptr: 0x%.8lX\n", (unsigned
long)output_ptr);
printf("bytes_out: 0x%.8lX\n", (unsigned
long)bytes_out);
error("ran out of input data");
}
inbuf = input_data;
insize = &input_data_end[0] - &input_data[0];
inptr = 1;
return inbuf[0];
}
/*
===========================================================================
* Write the output window window[0..outcnt-1] and
update crc and bytes_out.
* (Used for the decompressed data only.)
*/
void flush_window(void)
{
ulg c = crc;
unsigned n;
uch *in, *out, ch;
in = window;
out = &output_data[output_ptr];
for (n = 0; n < outcnt; n++) {
ch = *out++ = *in++;
c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
}
crc = c;
bytes_out += (ulg)outcnt;
output_ptr += (ulg)outcnt;
outcnt = 0;
puts(".");
}
static void error(char *x)
{
puts("\n\n");
puts(x);
puts("\n\n -- System halted");
while(1); /* Halt */
}
#define STACK_SIZE (4096)
long user_stack[STACK_SIZE]; /* 16KB stack */
long *stack_start = &user_stack[STACK_SIZE];
void decompress_kernel(void)
{
output_data = (uch *)TEXTADDR;
free_mem_ptr = (long)&_end;
free_mem_end_ptr = free_mem_ptr + HEAP_SIZE;
makecrc();
puts("Uncompressing Linux...");
gunzip();
puts(" done, booting the kernel.\n");
}
--------------------------------------------------------------------
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