Re: [Xen-devel] [PATCH 4/4] x86: check for multiboot{1, 2} header presence

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.06.19 at 16:40, <roger.pau@xxxxxxxxxx> wrote:
> On Wed, Jun 19, 2019 at 07:08:52AM -0600, Jan Beulich wrote:
>> >>> On 19.06.19 at 13:02, <roger.pau@xxxxxxxxxx> wrote:
>> > After building the hypervisor binary. Note that the check is performed
>> > by searching for the magic header value at the start of the binary.
>> > 
>> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> > ---
>> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> > Cc: Wei Liu <wl@xxxxxxx>
>> > ---
>> >  xen/arch/x86/Makefile | 3 +++
>> >  1 file changed, 3 insertions(+)
>> > 
>> > diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
>> > index 8a8d8f060f..9bb3bf6e6c 100644
>> > --- a/xen/arch/x86/Makefile
>> > +++ b/xen/arch/x86/Makefile
>> > @@ -102,6 +102,9 @@ 
>> > syms-warn-dup-$(CONFIG_SUPPRESS_DUPLICATE_SYMBOL_WARNINGS) :=
>> >  $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
>> >    ./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TARGET) 
>> > $(XEN_IMG_OFFSET) \
>> >                   `$(NM) $(TARGET)-syms | sed -ne 's/^\([^ ]*\) . 
> __2M_rwdata_end$$/0x\1/p'`
>> > +  # Check for multiboot{1,2} headers
>> > +  od -t x4 -N 8192 $(TARGET) | grep 1badb002 > /dev/null
>> > +  od -t x4 -N 32768 $(TARGET) | grep e85250d6 > /dev/null
>> 
>> What's the behavior when a signature is _not _ found? Will
>> $(TARGET) get deleted (by make)? I don't think it would (as we
>> don't specific .DELETE_ON_ERROR anywhere), so a subsequent
>> rebuild may not even execute this rule, and hence may look to be
>> successful despite it not actually having been.
> 
> Oh, right. It should be:
> 
> od -t x4 -N 8192 $(TARGET) | grep 1badb002 > /dev/null || (rm -rf $(TARGET); 
> exit 1)
> od -t x4 -N 32768 $(TARGET) | grep e85250d6 > /dev/null || (rm -rf $(TARGET); 
> exit 1)
> 
> Would you be OK with the above runes?

Not really, I'm afraid. This still wouldn't cope with an interrupted
build. I think it needs to be made work via an intermediate target,
or some other make trickery.

Jan


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