Re: [Xen-devel] [PATCH v6 10/15] x86/boot: implement early command line parser in C

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.09.16 at 17:27, <daniel.kiper@xxxxxxxxxx> wrote:
> On Mon, Sep 19, 2016 at 06:47:50AM -0600, Jan Beulich wrote:
>> >>> On 12.09.16 at 22:18, <daniel.kiper@xxxxxxxxxx> wrote:
> 
> [...]
> 
>> > --- a/xen/arch/x86/boot/trampoline.S
>> > +++ b/xen/arch/x86/boot/trampoline.S
>> > @@ -220,8 +220,22 @@ trampoline_boot_cpu_entry:
>> >          /* Jump to the common bootstrap entry point. */
>> >          jmp     trampoline_protmode_entry
>> >
>> > +#include "video.h"
>> > +
>> > +        .align  2
>> > +        .byte   0
>>
>> While this odd placement of the requested padding byte will fulfill
>> the immediate purpose, please do it the originally requested more
>> conventional way (putting it inside the structure and adding a
>> respective field to the C representation). For someone wanting to
>> add another field it'll then be far more obvious what to do without
>> re-introducing mis-alignment.
> 
> OK, however, I am still thinking how to automatically synchronize C and
> assembly early_boot_opts struct definitions or generate one from another.
> This way we can avoid __packed attribute and probably do not care about
> member alignments at all. Do you have an idea how to do that?

I would have ideas, but I think they're all not really suitable for this
little bit of data. If we had this problem in a more widespread manner,
then perhaps. But we're actually aiming at reducing the amount of
assembly language use.

Jan


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