[PATCH] i386: Relocatable kernel support
This patch modifies the i386 kernel so that if CONFIG_RELOCATABLE is selected it will be able to be loaded at any 4K aligned address below 1G. The technique used is to compile the decompressor with -fPIC and modify it so the decompressor is fully relocatable. For the main kernel relocations are generated. Resulting in a kernel that is relocatable with no runtime overhead and no need to modify the source code. A reserved 32bit word in the parameters has been assigned to serve as a stack so we figure out where are running. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com> Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Eric W. Biederman
committed by
Andi Kleen
Andi Kleen
parent
fd593d1277
commit
968de4f026
@@ -13,6 +13,88 @@
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#include <linux/vmalloc.h>
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#include <linux/screen_info.h>
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#include <asm/io.h>
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#include <asm/page.h>
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/* WARNING!!
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* This code is compiled with -fPIC and it is relocated dynamically
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* at run time, but no relocation processing is performed.
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* This means that it is not safe to place pointers in static structures.
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*/
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/*
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* Getting to provable safe in place decompression is hard.
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* Worst case behaviours need to be analized.
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* Background information:
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*
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* The file layout is:
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* magic[2]
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* method[1]
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* flags[1]
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* timestamp[4]
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* extraflags[1]
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* os[1]
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* compressed data blocks[N]
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* crc[4] orig_len[4]
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*
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* resulting in 18 bytes of non compressed data overhead.
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*
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* Files divided into blocks
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* 1 bit (last block flag)
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* 2 bits (block type)
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*
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* 1 block occurs every 32K -1 bytes or when there 50% compression has been achieved.
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* The smallest block type encoding is always used.
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*
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* stored:
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* 32 bits length in bytes.
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*
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* fixed:
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* magic fixed tree.
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* symbols.
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*
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* dynamic:
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* dynamic tree encoding.
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* symbols.
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*
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*
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* The buffer for decompression in place is the length of the
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* uncompressed data, plus a small amount extra to keep the algorithm safe.
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* The compressed data is placed at the end of the buffer. The output
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* pointer is placed at the start of the buffer and the input pointer
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* is placed where the compressed data starts. Problems will occur
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* when the output pointer overruns the input pointer.
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*
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* The output pointer can only overrun the input pointer if the input
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* pointer is moving faster than the output pointer. A condition only
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* triggered by data whose compressed form is larger than the uncompressed
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* form.
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*
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* The worst case at the block level is a growth of the compressed data
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* of 5 bytes per 32767 bytes.
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*
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* The worst case internal to a compressed block is very hard to figure.
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* The worst case can at least be boundined by having one bit that represents
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* 32764 bytes and then all of the rest of the bytes representing the very
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* very last byte.
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*
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* All of which is enough to compute an amount of extra data that is required
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* to be safe. To avoid problems at the block level allocating 5 extra bytes
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* per 32767 bytes of data is sufficient. To avoind problems internal to a block
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* adding an extra 32767 bytes (the worst case uncompressed block size) is
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* sufficient, to ensure that in the worst case the decompressed data for
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* block will stop the byte before the compressed data for a block begins.
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* To avoid problems with the compressed data's meta information an extra 18
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* bytes are needed. Leading to the formula:
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*
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* extra_bytes = (uncompressed_size >> 12) + 32768 + 18 + decompressor_size.
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*
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* Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
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* Adding 32768 instead of 32767 just makes for round numbers.
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* Adding the decompressor_size is necessary as it musht live after all
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* of the data as well. Last I measured the decompressor is about 14K.
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* 10K of actuall data and 4K of bss.
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*
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*/
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/*
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* gzip declarations
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@@ -29,15 +111,20 @@ typedef unsigned char uch;
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typedef unsigned short ush;
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typedef unsigned long ulg;
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#define WSIZE 0x8000 /* Window size must be at least 32k, */
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/* and a power of two */
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#define WSIZE 0x80000000 /* Window size must be at least 32k,
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* and a power of two
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* We don't actually have a window just
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* a huge output buffer so I report
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* a 2G windows size, as that should
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* always be larger than our output buffer.
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*/
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static uch *inbuf; /* input buffer */
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static uch window[WSIZE]; /* Sliding window buffer */
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static uch *inbuf; /* input buffer */
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static uch *window; /* Sliding window buffer, (and final output buffer) */
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static unsigned insize = 0; /* valid bytes in inbuf */
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static unsigned inptr = 0; /* index of next byte to be processed in inbuf */
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static unsigned outcnt = 0; /* bytes in output buffer */
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static unsigned insize; /* valid bytes in inbuf */
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static unsigned inptr; /* index of next byte to be processed in inbuf */
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static unsigned outcnt; /* bytes in output buffer */
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/* gzip flag byte */
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#define ASCII_FLAG 0x01 /* bit 0 set: file probably ASCII text */
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@@ -88,8 +175,6 @@ extern unsigned char input_data[];
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extern int input_len;
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static long bytes_out = 0;
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static uch *output_data;
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static unsigned long output_ptr = 0;
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static void *malloc(int size);
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static void free(void *where);
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@@ -99,17 +184,10 @@ static void *memcpy(void *dest, const void *src, unsigned n);
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static void putstr(const char *);
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extern int end;
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static long free_mem_ptr = (long)&end;
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static long free_mem_end_ptr;
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static unsigned long free_mem_ptr;
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static unsigned long free_mem_end_ptr;
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#define INPLACE_MOVE_ROUTINE 0x1000
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#define LOW_BUFFER_START 0x2000
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#define LOW_BUFFER_MAX 0x90000
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#define HEAP_SIZE 0x3000
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static unsigned int low_buffer_end, low_buffer_size;
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static int high_loaded =0;
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static uch *high_buffer_start /* = (uch *)(((ulg)&end) + HEAP_SIZE)*/;
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static char *vidmem = (char *)0xb8000;
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static int vidport;
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@@ -150,7 +228,7 @@ static void gzip_mark(void **ptr)
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static void gzip_release(void **ptr)
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{
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free_mem_ptr = (long) *ptr;
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free_mem_ptr = (unsigned long) *ptr;
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}
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static void scroll(void)
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@@ -178,7 +256,7 @@ static void putstr(const char *s)
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y--;
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}
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} else {
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vidmem [ ( x + cols * y ) * 2 ] = c;
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vidmem [ ( x + cols * y ) * 2 ] = c;
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if ( ++x >= cols ) {
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x = 0;
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if ( ++y >= lines ) {
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@@ -223,58 +301,31 @@ static void* memcpy(void* dest, const void* src, unsigned n)
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*/
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static int fill_inbuf(void)
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{
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if (insize != 0) {
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error("ran out of input data");
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}
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inbuf = input_data;
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insize = input_len;
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inptr = 1;
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return inbuf[0];
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error("ran out of input data");
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return 0;
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}
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/* ===========================================================================
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* Write the output window window[0..outcnt-1] and update crc and bytes_out.
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* (Used for the decompressed data only.)
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*/
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static void flush_window_low(void)
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{
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ulg c = crc; /* temporary variable */
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unsigned n;
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uch *in, *out, ch;
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in = window;
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out = &output_data[output_ptr];
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for (n = 0; n < outcnt; n++) {
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ch = *out++ = *in++;
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c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
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}
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crc = c;
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bytes_out += (ulg)outcnt;
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output_ptr += (ulg)outcnt;
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outcnt = 0;
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}
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static void flush_window_high(void)
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{
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ulg c = crc; /* temporary variable */
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unsigned n;
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uch *in, ch;
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in = window;
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for (n = 0; n < outcnt; n++) {
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ch = *output_data++ = *in++;
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if ((ulg)output_data == low_buffer_end) output_data=high_buffer_start;
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c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
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}
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crc = c;
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bytes_out += (ulg)outcnt;
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outcnt = 0;
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}
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static void flush_window(void)
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{
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if (high_loaded) flush_window_high();
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else flush_window_low();
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/* With my window equal to my output buffer
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* I only need to compute the crc here.
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*/
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ulg c = crc; /* temporary variable */
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unsigned n;
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uch *in, ch;
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in = window;
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for (n = 0; n < outcnt; n++) {
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ch = *in++;
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c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
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}
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crc = c;
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bytes_out += (ulg)outcnt;
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outcnt = 0;
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}
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static void error(char *x)
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@@ -286,66 +337,8 @@ static void error(char *x)
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while(1); /* Halt */
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}
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#define STACK_SIZE (4096)
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long user_stack [STACK_SIZE];
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struct {
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long * a;
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short b;
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} stack_start = { & user_stack [STACK_SIZE] , __BOOT_DS };
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static void setup_normal_output_buffer(void)
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{
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#ifdef STANDARD_MEMORY_BIOS_CALL
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if (RM_EXT_MEM_K < 1024) error("Less than 2MB of memory");
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#else
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if ((RM_ALT_MEM_K > RM_EXT_MEM_K ? RM_ALT_MEM_K : RM_EXT_MEM_K) < 1024) error("Less than 2MB of memory");
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#endif
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output_data = (unsigned char *)CONFIG_PHYSICAL_START; /* Normally Points to 1M */
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free_mem_end_ptr = (long)real_mode;
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}
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struct moveparams {
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uch *low_buffer_start; int lcount;
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uch *high_buffer_start; int hcount;
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};
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static void setup_output_buffer_if_we_run_high(struct moveparams *mv)
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{
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high_buffer_start = (uch *)(((ulg)&end) + HEAP_SIZE);
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#ifdef STANDARD_MEMORY_BIOS_CALL
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if (RM_EXT_MEM_K < (3*1024)) error("Less than 4MB of memory");
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#else
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if ((RM_ALT_MEM_K > RM_EXT_MEM_K ? RM_ALT_MEM_K : RM_EXT_MEM_K) < (3*1024)) error("Less than 4MB of memory");
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#endif
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mv->low_buffer_start = output_data = (unsigned char *)LOW_BUFFER_START;
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low_buffer_end = ((unsigned int)real_mode > LOW_BUFFER_MAX
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? LOW_BUFFER_MAX : (unsigned int)real_mode) & ~0xfff;
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low_buffer_size = low_buffer_end - LOW_BUFFER_START;
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high_loaded = 1;
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free_mem_end_ptr = (long)high_buffer_start;
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if ( (CONFIG_PHYSICAL_START + low_buffer_size) > ((ulg)high_buffer_start)) {
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high_buffer_start = (uch *)(CONFIG_PHYSICAL_START + low_buffer_size);
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mv->hcount = 0; /* say: we need not to move high_buffer */
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}
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else mv->hcount = -1;
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mv->high_buffer_start = high_buffer_start;
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}
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static void close_output_buffer_if_we_run_high(struct moveparams *mv)
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{
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if (bytes_out > low_buffer_size) {
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mv->lcount = low_buffer_size;
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if (mv->hcount)
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mv->hcount = bytes_out - low_buffer_size;
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} else {
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mv->lcount = bytes_out;
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mv->hcount = 0;
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}
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}
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asmlinkage int decompress_kernel(struct moveparams *mv, void *rmode)
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asmlinkage void decompress_kernel(void *rmode, unsigned long end,
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uch *input_data, unsigned long input_len, uch *output)
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{
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real_mode = rmode;
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@@ -360,13 +353,25 @@ asmlinkage int decompress_kernel(struct moveparams *mv, void *rmode)
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lines = RM_SCREEN_INFO.orig_video_lines;
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cols = RM_SCREEN_INFO.orig_video_cols;
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if (free_mem_ptr < 0x100000) setup_normal_output_buffer();
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else setup_output_buffer_if_we_run_high(mv);
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window = output; /* Output buffer (Normally at 1M) */
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free_mem_ptr = end; /* Heap */
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free_mem_end_ptr = end + HEAP_SIZE;
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inbuf = input_data; /* Input buffer */
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insize = input_len;
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inptr = 0;
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if (((u32)output - CONFIG_PHYSICAL_START) & 0x3fffff)
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error("Destination address not 4M aligned");
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if (end > ((-__PAGE_OFFSET-(512 <<20)-1) & 0x7fffffff))
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error("Destination address too large");
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#ifndef CONFIG_RELOCATABLE
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if ((u32)output != CONFIG_PHYSICAL_START)
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error("Wrong destination address");
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#endif
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makecrc();
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putstr("Uncompressing Linux... ");
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gunzip();
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putstr("Ok, booting the kernel.\n");
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if (high_loaded) close_output_buffer_if_we_run_high(mv);
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return high_loaded;
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return;
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}
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