[v3] hw/i386/pc: prompt not multboot or morden kernel image

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.

Signed-off-by: liguang <lig.fnst@cn.fujitsu.com>
---
 hw/i386/pc.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

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.fnst@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). In that case,
the error message above would also be misleading.

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. :)

Jesse Larrew
Software Engineer, KVM Team
IBM Linux Technology Center
Phone: (512) 973-2052 (T/L: 363-2052)
jlarrew@linux.vnet.ibm.com

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.fnst@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") :-)

> 
> 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

> 
> Jesse Larrew
> Software Engineer, KVM Team
> IBM Linux Technology Center
> Phone: (512) 973-2052 (T/L: 363-2052)
> jlarrew@linux.vnet.ibm.com
>