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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] readnote: Add bzImage kernel support
On Thu, 2012-04-26 at 10:13 +0100, Jan Beulich wrote:
> >>> On 26.04.12 at 10:54, Xuesen Guo <Xuesen.Guo@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > Add the check of bzImage kernel and make it work
> > with RHEL 6 bzipped kernels
>
> I fail to see the relation of the term "bzipped" above to the actual patch.
Oh yes, this is a common misconception (which I failed to notice in my
review).
The "bz" in bzImage does not refer to the bzip compression algorithm.
Rather it refers to "big zImage". It's a historical thing because the
original zImage compressor was restricted to <1M (or something) of RAM
at decompression time and bzImage was introduced to cope with more and
therefore worked for larger kernels. Obviously 1M is very limiting to in
practice everyone uses bzImage today...
Now of course today, just to add to the confusion, bzImage can support
multiple compression algorithms, including the original z, but also
bzip2, lzma and xz.
Ian
>
> Jan
>
> > Signed-off-by: Xuesen Guo <Xuesen.Guo@xxxxxxxxxxxxxxxxxxxxx>
> >
> > ---
> > Changed since v1:
> > * add additional checks of the offset and length
> > * not changing st.st_size, use size instead of st.st_size
> >
> > diff -r d690c7e896a2 -r 27a6422ac06d tools/xcutils/readnotes.c
> > --- a/tools/xcutils/readnotes.c Thu Apr 05 11:06:03 2012 +0100
> > +++ b/tools/xcutils/readnotes.c Thu Apr 26 16:53:17 2012 +0800
> > @@ -18,6 +18,48 @@
> >
> > static xc_interface *xch;
> >
> > +/* According to the implemation of xc_dom_probe_bzimage_kernel() function
> > */
> > +/* We add support of bzImage kernel */
> > +/* Copied from tools/libxc/xc_doom_bzImageloader.c */
> > +struct setup_header {
> > + uint8_t _pad0[0x1f1]; /* skip uninteresting stuff */
> > + uint8_t setup_sects;
> > + uint16_t root_flags;
> > + uint32_t syssize;
> > + uint16_t ram_size;
> > + uint16_t vid_mode;
> > + uint16_t root_dev;
> > + uint16_t boot_flag;
> > + uint16_t jump;
> > + uint32_t header;
> > +#define HDR_MAGIC "HdrS"
> > +#define HDR_MAGIC_SZ 4
> > + uint16_t version;
> > +#define VERSION(h,l) (((h)<<8) | (l))
> > + uint32_t realmode_swtch;
> > + uint16_t start_sys;
> > + uint16_t kernel_version;
> > + uint8_t type_of_loader;
> > + uint8_t loadflags;
> > + uint16_t setup_move_size;
> > + uint32_t code32_start;
> > + uint32_t ramdisk_image;
> > + uint32_t ramdisk_size;
> > + uint32_t bootsect_kludge;
> > + uint16_t heap_end_ptr;
> > + uint16_t _pad1;
> > + uint32_t cmd_line_ptr;
> > + uint32_t initrd_addr_max;
> > + uint32_t kernel_alignment;
> > + uint8_t relocatable_kernel;
> > + uint8_t _pad2[3];
> > + uint32_t cmdline_size;
> > + uint32_t hardware_subarch;
> > + uint64_t hardware_subarch_data;
> > + uint32_t payload_offset;
> > + uint32_t payload_length;
> > +} __attribute__((packed));
> > +
> > static void print_string_note(const char *prefix, struct elf_binary *elf,
> > const elf_note *note)
> > {
> > @@ -131,6 +173,9 @@ int main(int argc, char **argv)
> > const elf_shdr *shdr;
> > int notes_found = 0;
> >
> > + struct setup_header *hdr;
> > + uint64_t payload_offset, payload_length;
> > +
> > if (argc != 2)
> > {
> > fprintf(stderr, "Usage: readnotes <elfimage>\n");
> > @@ -159,13 +204,45 @@ int main(int argc, char **argv)
> > fprintf(stderr, "Unable to map %s: %s\n", f, strerror(errno));
> > return 1;
> > }
> > - size = st.st_size;
> > +
> > + /* Check the magic of bzImage kernel */
> > + hdr = (struct setup_header *)image;
> > + if ( memcmp(&hdr->header, HDR_MAGIC, HDR_MAGIC_SZ) == 0 )
> > + {
> > + if ( hdr->version < VERSION(2,8) )
> > + {
> > + printf("%s: boot protocol too old (%04x)",
> > __FUNCTION__, hdr->version);
> > + return 1;
> > + }
> >
> > - usize = xc_dom_check_gzip(xch, image, st.st_size);
> > + /* upcast to 64 bits to avoid overflow */
> > + /* setup_sects is u8 and so cannot overflow */
> > + payload_offset = (hdr->setup_sects + 1) * 512;
> > + payload_offset += hdr->payload_offset;
> > + payload_length = hdr->payload_length;
> > +
> > + if ( payload_offset >= st.st_size )
> > + {
> > + printf("%s: payload offset overflow", __FUNCTION__);
> > + return 1;
> > + }
> > + if ( (payload_offset + payload_length) > st.st_size )
> > + {
> > + printf("%s: payload length overflow", __FUNCTION__);
> > + return 1;
> > + }
> > +
> > + image = image + payload_offset;
> > + size = payload_length;
> > + } else {
> > + size = st.st_size;
> > + }
> > +
> > + usize = xc_dom_check_gzip(xch, image, size);
> > if (usize)
> > {
> > tmp = malloc(usize);
> > - xc_dom_do_gunzip(xch, image, st.st_size, tmp, usize);
> > + xc_dom_do_gunzip(xch, image, size, tmp, usize);
> > image = tmp;
> > size = usize;
> > }
> >
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