Re: [PATCH] x86/boot: This program cannot be run in DOS mode.$

[Pavel Machek <pavel@ucw.cz>]

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On Mon 2019-04-08 20:08:09, Pali Rohár wrote:
> On Monday 08 April 2019 20:04:22 Pavel Machek wrote:
> > On Mon 2019-04-01 12:24:34, Pali Rohár wrote:
> > > Every EFI binary is in PE format. And we know that PE format needs to have
> > > MZ MS-DOS header as there is written offset to PE header.
> > > 
> > > Therefore generated bzImage binary with CONFIG_EFI_STUB option is MS-DOS
> > > executable binary.
> > > 
> > > We already know the "requirement" that Windows PE executable started in
> > > MS-DOS must print legendary and famous message to computer screen:
> > > "This program cannot be run in DOS mode."
> > > 
> > > But trying to run that bzImage of Linux kernel with MZ header just cause
> > > freezing whole MS-DOS instead of writing "the correct message" to user.
> > > This is not the compliant behavior of PE executables!
> > > 
> > > This patch fixes this problem. When Linux kernel compiled with
> > > CONFIG_EFI_STUB is started in MS-DOS then it prints message:
> > > 
> > >   This program cannot be run in DOS mode.
> > >   To load Linux kernel from DOS mode use LOADLIN.EXE.
> > > 
> > > So it also helps MS-DOS users how to "correctly" start this bzImage binary
> > > by mentioning LOADLIN.EXE. Note that MS-DOS strings are not null-terminated
> > > but rather dollar-terminated.
> > > 
> > > To have error message unified bugger_off_msg for BIOS boot block code was
> > > changed to:
> > > 
> > >   This program cannot be run in BIOS mode.
> > > 
> > > So if you copy generated bzImage directly to boot sector and try to boot it
> > > by BIOS you get this new updated message.
> > > 
> > > Due to fixed offset of setup header (0x1f1), PE header was moved after
> > > entrytext section. bstext and bsdata sections where is full MZ header and
> > > MS-DOS code is now bigger.
> > 
> > Hehe, I guess the patch may have been dropped due to april's fools?
> 
> Yea, it was mean as first April patch :-) I tested it with MS-DOS 7.0
> and DOSBox and it worked.
> 
> > You may want to retransmit?
> 
> Do you really think it can be useful? :-)

Dunno. It is quite simple, and quite a nice hack ;-).

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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