在 2013-04-09二的 14:15 -0500，Jesse Larrew写道：
> On 04/09/2013 12:05 AM, li guang wrote:
> > 在 2013-04-08一的 23:36 -0500，Jesse Larrew写道：
> >> On 04/08/2013 09:27 PM, liguang wrote:
> >>> if head magic is missing or wrong unexpectedly, we'd
> >>> better to prompt memssage for this.
> >>> e.g.
> >>> I make a mistake to boot a vmlinuz for MIPS(which
> >>> I think it's for x86) like this:
> >>> qemu-system-x86_64 -kernel vmlinuz -initrd demord
> >>> then qemu report:
> >>> "qemu: linux kernel too old to load a ram disk"
> >>> that's misleading.
> >>>
> >>
> >> Yes, that message would definitely be misleading in this case.
> >>
> >>> Signed-off-by: liguang <lig.f...@cn.fujitsu.com>
> >>> ---
> >>> hw/i386/pc.c | 2 ++
> >>> 1 files changed, 2 insertions(+), 0 deletions(-)
> >>>
> >>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> >>> index ebbf059..6b29c3f 100644
> >>> --- a/hw/i386/pc.c
> >>> +++ b/hw/i386/pc.c
> >>> @@ -686,6 +686,8 @@ static void load_linux(void *fw_cfg,
> >>> if (load_multiboot(fw_cfg, f, kernel_filename, initrd_filename,
> >>> kernel_cmdline, kernel_size, header)) {
> >>> return;
> >>> + } else {
> >>> + fprintf(stderr, "warn: invalid multiboot or modern kernel
> >>> image\n");
> >>> }
> >>> protocol = 0;
> >>> }
> >>>
> >>
> >> My impression from reading through the code is that this branch can be
> >> legitimately triggered by an older kernel (protocol < 0x200).
> >
> > right.
> >
> >> In that case,the error message above would also be misleading.
> >
> > the warning message is saying: hey, we prefer modern kernel image
> > or multiboot, but you specify neither, what are you doing?
> > do you want to boot an old(obsolete) kernel?
> >
> > or, add a line like fprintf(stderr, "do you boot an old kernel?\n") :-)
> >
>
> Ah, I understand now. Thanks for explaining that. :)
>
> >>
> >> I think a better solution might be to simply validate that the arch
> >> specified in the ELF header matches the arch that qemu is emulating.
> >> I'll look into this more tomorrow morning. :)
> >
> > that's fine
> >
>
> Looking at Documentation/x86/boot.txt in the kernel source, it looks
> like there is a separate word of header magic that all x86 kernels should
> have -- even the oldest images. Adding a separate check for that magic
> might be a more complete solution:
>
> ---
> hw/i386/pc.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 8d75b34..e120427 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -686,6 +686,14 @@ static void load_linux(void *fw_cfg,
> if (load_multiboot(fw_cfg, f, kernel_filename, initrd_filename,
> kernel_cmdline, kernel_size, header)) {
> return;
> + } else {
> + /* This is the closest thing old Linux kernels have to a
> + magic number. */
> + if (lduw_p(header+0x01FE) != 0xAA55) {
maybe a good candidate,
but, AFAIK, 0xAA55 can hardly be a magic for
it's commonly used by many cases.
> + fprintf(stderr, "qemu: '%s' is not an x86 kernel image.\n",
> + kernel_filename);
> + exit(1);
> + }
> }
> protocol = 0;
> }
