Messages in this thread | | | Date | Mon, 8 Apr 2019 20:04:22 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] x86/boot: This program cannot be run in DOS mode.$ |
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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?
You may want to retransmit? Pavel
> Signed-off-by: Pali Rohár <pali.rohar@gmail.com> > --- > arch/x86/boot/header.S | 55 +++++++++++++++++++++++++++++++++++++++++++------- > arch/x86/boot/setup.ld | 1 + > 2 files changed, 49 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S > index 850b8762e889..58fcab7d00c8 100644 > --- a/arch/x86/boot/header.S > +++ b/arch/x86/boot/header.S > @@ -45,6 +45,46 @@ bootsect_start: > # "MZ", MS-DOS header > .byte 0x4d > .byte 0x5a > + > + # Explicitly enter this as bytes, or the assembler > + # tries to generate a 3-byte jump here, which causes > + # everything else to push off to the wrong offset. > + .byte 0xeb # short (2-byte) jump > + .byte bios_start-1f > +1: > + > + .org 0x04 > + .short 3 # e_cp - Pages in file > + .short 0 # e_crlc - Relocations > + .short 4 # e_cparhdr - Size of header in paragraphs > + .short 0 # e_minalloc - Minimum extra paragraphs needed > + .short 0xffff # e_maxalloc - Maximum extra paragraphs needed > + .short 0 # e_ss - Initial (relative) SS value > + .short 0 # e_sp - Initial SP value > + .short 0 # e_csum - Checksum > + .short 0 # e_ip - Initial IP value > + .short -4 # e_cs - Initial (relative) CS value > + .short 0x40 # e_lfarlc - File address of relocation table > + > + .org 0x3c > + .long pe_header # Offset to the PE header > + > + # > + # MS-DOS start code > + # > + push %cs > + pop %ds > + > + # Write msdos_msg string > + mov $msdos_msg, %dx > + mov $0x09, %ah > + int $0x21 > + > + # Terminate program > + mov $0x4c01, %ax > + int $0x21 > + > +bios_start: > #endif > > # Normalize the start address > @@ -80,22 +120,23 @@ bs_die: > # invoke the BIOS reset code... > ljmp $0xf000,$0xfff0 > > + .section ".bsdata", "a" > #ifdef CONFIG_EFI_STUB > - .org 0x3c > - # > - # Offset to the PE header. > - # > - .long pe_header > +msdos_msg: > + .ascii "This program cannot be run in DOS mode.\r\n" > + .ascii "To load Linux kernel from DOS mode use LOADLIN.EXE.\r\r\n" > + .ascii "$" > #endif /* CONFIG_EFI_STUB */ > > - .section ".bsdata", "a" > bugger_off_msg: > - .ascii "Use a boot loader.\r\n" > + .ascii "This program cannot be run in BIOS mode.\r\n" > + .ascii "To load Linux kernel from BIOS mode use a boot loader.\r\n" > .ascii "\n" > .ascii "Remove disk and press any key to reboot...\r\n" > .byte 0 > > #ifdef CONFIG_EFI_STUB > + .section ".pedata", "a" > pe_header: > .ascii "PE" > .word 0 > diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld > index 0149e41d42c2..c0ec2fe09d2d 100644 > --- a/arch/x86/boot/setup.ld > +++ b/arch/x86/boot/setup.ld > @@ -16,6 +16,7 @@ SECTIONS > . = 495; > .header : { *(.header) } > .entrytext : { *(.entrytext) } > + .pedata : { *(.pedata) } > .inittext : { *(.inittext) } > .initdata : { *(.initdata) } > __end_init = .;
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