diff options
| -rw-r--r-- | Documentation/lguest/lguest.c | 93 |
1 files changed, 29 insertions, 64 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c index 004c5c6aba6a..3949620e42fa 100644 --- a/Documentation/lguest/lguest.c +++ b/Documentation/lguest/lguest.c @@ -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; - - /* 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"); + u8 hdr[1024]; + int r; + /* Modern bzImages get loaded at 1M. */ + void *p = from_guest_phys(0x100000); + + /* 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 |