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#include "boot.h"
#include "squeeze.h"
/*
* for details of `unsqueeze' see:
*
* %A Mark Taunton
* %T Compressed Executables: An Exercise in Thinking Small
* %P 385-404
* %I USENIX
* %B USENIX Conference Proceedings
* %D Summer 1991
* %C Nashville, TN
*
* several of the unimplemented improvements described in the paper
* have been implemented here
*
* there is a further transformation on the powerpc (QFLAG!=0) to shuffle bits
* in certain instructions so as to push the fixed bits to the top of the word.
*/
#define EXECHDRLEN (8*4)
typedef struct Squeeze Squeeze;
struct Squeeze {
int n;
ulong tab[7*256];
};
#define GET4(p) (((((((p)[0]<<8)|(p)[1])<<8)|(p)[2])<<8)|(p)[3])
/*
* for speed of unsqueezing from Flash, certain checks are
* not done inside the loop (as they would be in the unsqueeze program zqs),
* but instead the checksum is expected to catch corrupted files.
* in fact the Squeeze array bounds can't be exceeded in practice
* because the tables are always full for a squeezed kernel.
*/
enum {
QFLAG = 1, /* invert powerpc-specific code transformation */
CHECK = 0, /* check precise bounds in Squeeze array (otherwise checksum detects error) */
};
static ulong chksum;
static int rdtab(Block*, Squeeze*, int);
static ulong* unsqueeze(ulong*, uchar*, uchar*, Squeeze*, Squeeze*, ulong);
static uchar* unsqzseg(uchar*, Block*, long, long, char*);
static Alarm* unsqzal;
int
issqueezed(uchar *b)
{
return GET4(b) == SQMAGIC? GET4(b+SQHDRLEN): 0;
}
static void
unsqzdot(Alarm*)
{
unsqzal = alarm(500, unsqzdot, nil);
print(".");
}
long
unsqueezef(Block *b, ulong *entryp)
{
uchar *loada, *wp;
ulong toptxt, topdat, oldsum;
long asis, nst, nsd;
Sqhdr *sqh;
Exec *ex;
if(BLEN(b) < SQHDRLEN+EXECHDRLEN)
return -1;
sqh = (Sqhdr*)b->rp;
if(GET4(sqh->magic) != SQMAGIC)
return -1;
chksum = 0;
toptxt = GET4(sqh->toptxt);
topdat = GET4(sqh->topdat);
oldsum = GET4(sqh->sum);
asis = GET4(sqh->asis);
nst = GET4(sqh->text);
nsd = GET4(sqh->data);
b->rp += SQHDRLEN;
ex = (Exec*)b->rp;
if(GET4(ex->magic) != Q_MAGIC){
print("zqs: not powerPC executable\n");
return -1;
}
*entryp = GET4(ex->entry);
b->rp += EXECHDRLEN;
loada = KADDR(PADDR(*entryp));
wp = unsqzseg(loada, b, nst, toptxt, "text");
if(wp == nil){
print("zqs: format error\n");
return -1;
}
if(nsd){
wp = (uchar*)PGROUND((ulong)wp);
wp = unsqzseg(wp, b, nsd, topdat, "data");
if(wp == nil){
print("zqs: format error\n");
return -1;
}
}
if(asis){
memmove(wp, b->rp, asis);
wp += asis;
b->rp += asis;
}
if(chksum != oldsum){
print("\nsqueezed kernel: checksum error: %8.8lux need %8.8lux\n", chksum, oldsum);
return -1;
}
return wp-loada;
}
static uchar *
unsqzseg(uchar *wp, Block *b, long ns, long top, char *what)
{
static Squeeze sq3, sq4;
print("unpack %s %8.8lux %lud:", what, wp, ns);
if(ns == 0)
return wp;
if(rdtab(b, &sq3, 0) < 0)
return nil;
if(rdtab(b, &sq4, 8) < 0)
return nil;
if(BLEN(b) < ns){
print(" **size error\n");
return nil;
}
unsqzal = alarm(500, unsqzdot, nil);
wp = (uchar*)unsqueeze((ulong*)wp, b->rp, b->rp+ns, &sq3, &sq4, top);
cancel(unsqzal);
unsqzal = nil;
print("\n");
if(wp == nil){
print("zqs: corrupt squeezed data stream\n");
return nil;
}
b->rp += ns;
return wp;
}
static ulong*
unsqueeze(ulong *wp, uchar *rp, uchar *ep, Squeeze *sq3, Squeeze *sq4, ulong top)
{
ulong nx, csum;
int code, n;
if(QFLAG){
QREMAP(top); /* adjust top just once, outside the loop */
}
csum = chksum;
while(rp < ep){
/* no function calls within this loop for speed */
code = *rp;
rp++;
n = 0;
nx = code>>4;
do{
if(nx == 0){
nx = top;
}else{
if(nx==1){
nx = (((((rp[3]<<8)|rp[2])<<8)|rp[1])<<8)|rp[0];
rp += 4;
}else if(nx <= 8){ /* 2 to 8 */
nx = ((nx-2)<<8) | rp[0];
if(CHECK && nx >= sq4->n)
return nil; /* corrupted file */
nx = sq4->tab[nx] | rp[1];
rp += 2;
}else{ /* 9 to 15 */
nx = ((nx-9)<<8) | rp[0];
if(CHECK && nx >= sq3->n)
return nil; /* corrupted file */
nx = sq3->tab[nx];
rp++;
}
if(rp > ep)
return nil; /* corrupted file */
if(QFLAG){
QREMAP(nx);
}
}
*wp = nx;
wp++;
csum += nx;
nx = code & 0xF;
}while(++n == 1);
}
chksum = csum;
return wp;
}
static int
rdtab(Block *b, Squeeze *sq, int shift)
{
uchar *p, *ep;
ulong v, w;
int i;
if(BLEN(b) < 2)
return -1;
i = (b->rp[0]<<8) | b->rp[1];
if(1)
print(" T%d", i);
b->rp += 2;
if((i -= 2) > 0){
if(BLEN(b) < i)
return -1;
}
sq->n = 0;
p = b->rp;
ep = b->rp+i;
b->rp += i;
v = 0;
while(p < ep){
w = 0;
do{
if(p >= ep)
return -1;
w = (w<<7) | (*p & 0x7F);
}while(*p++ & 0x80);
v += w;
if(0)
print("%d %8.8lux %8.8lux\n", sq->n, v, w);
sq->tab[sq->n++] = v<<shift;
}
return 0;
}
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