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Loading bzImage directly. 

Now arch/i386/boot/compressed/head.S understands the hardware_platform field,
we can directly execute bzImages.  No more horrific unpacking code.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2007-10-22 11:29:56 +10:00
parent 814a0e5cdf
commit 5bbf89fc26
1 changed files with 28 additions and 63 deletions
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91
Documentation/lguest/lguest.c
View File

@ -326,74 +326,39 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
return ehdr->e_entry;
}
/*L:160 Unfortunately the entire ELF image isn't compressed: the segments
* which need loading are extracted and compressed raw. This denies us the
* information we need to make a fully-general loader. */
static unsigned long unpack_bzimage(int fd)
{
gzFile f;
int ret, len = 0;
/* A bzImage always gets loaded at physical address 1M. This is
* actually configurable as CONFIG_PHYSICAL_START, but as the comment
* there says, "Don't change this unless you know what you are doing".
* Indeed. */
void *img = from_guest_phys(0x100000);
/* gzdopen takes our file descriptor (carefully placed at the start of
* the GZIP header we found) and returns a gzFile. */
f = gzdopen(fd, "rb");
/* We read it into memory in 64k chunks until we hit the end. */
while ((ret = gzread(f, img + len, 65536)) > 0)
len += ret;
if (ret < 0)
err(1, "reading image from bzImage");
verbose("Unpacked size %i addr %p\n", len, img);
/* The entry point for a bzImage is always the first byte */
return (unsigned long)img;
}
/*L:150 A bzImage, unlike an ELF file, is not meant to be loaded. You're
* supposed to jump into it and it will unpack itself. We can't do that
* because the Guest can't run the unpacking code, and adding features to
* lguest kills puppies, so we don't want to.
* supposed to jump into it and it will unpack itself. We used to have to
* perform some hairy magic because the unpacking code scared me.
*
* The bzImage is formed by putting the decompressing code in front of the
* compressed kernel code. So we can simple scan through it looking for the
* first "gzip" header, and start decompressing from there. */
* Fortunately, Jeremy Fitzhardinge convinced me it wasn't that hard and wrote
* a small patch to jump over the tricky bits in the Guest, so now we just read
* the funky header so we know where in the file to load, and away we go! */
static unsigned long load_bzimage(int fd)
{
unsigned char c;
int state = 0;
u8 hdr[1024];
int r;
/* Modern bzImages get loaded at 1M. */
void *p = from_guest_phys(0x100000);
/* GZIP header is 0x1F 0x8B <method> <flags>... <compressed-by>. */
while (read(fd, &c, 1) == 1) {
switch (state) {
case 0:
if (c == 0x1F)
state++;
break;
case 1:
if (c == 0x8B)
state++;
else
state = 0;
break;
case 2 ... 8:
state++;
break;
case 9:
/* Seek back to the start of the gzip header. */
lseek(fd, -10, SEEK_CUR);
/* One final check: "compressed under UNIX". */
if (c != 0x03)
state = -1;
else
return unpack_bzimage(fd);
}
}
errx(1, "Could not find kernel in bzImage");
/* Go back to the start of the file and read the header. It should be
* a Linux boot header (see Documentation/i386/boot.txt) */
lseek(fd, 0, SEEK_SET);
read(fd, hdr, sizeof(hdr));
/* At offset 0x202, we expect the magic "HdrS" */
if (memcmp(hdr + 0x202, "HdrS", 4) != 0)
errx(1, "This doesn't look like a bzImage to me");
/* The byte at 0x1F1 tells us how many extra sectors of
* header: skip over them all. */
lseek(fd, (unsigned long)(hdr[0x1F1]+1) * 512, SEEK_SET);
/* Now read everything into memory. in nice big chunks. */
while ((r = read(fd, p, 65536)) > 0)
p += r;
/* Finally, 0x214 tells us where to start the kernel. */
return *(unsigned long *)&hdr[0x214];
}
/*L:140 Loading the kernel is easy when it's a "vmlinux", but most kernels