From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH] Fix efifb initialisation when the only GOP device implements ConOut. Date: Mon, 07 Jan 2013 17:51:20 +0000 Message-ID: <1357581080.2844.17.camel@shinybook.infradead.org> References: <1357431222.9270.73.camel@shinybook.infradead.org> <1357524250.9270.86.camel@shinybook.infradead.org> <1357578923.8203.72.camel@mfleming-mobl1.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-86T6zooNpA1TN67k25FP" Return-path: In-Reply-To: <1357578923.8203.72.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matt Fleming Cc: x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, Matthew Garrett , "H. Peter Anvin" , linux-efi List-Id: linux-efi@vger.kernel.org --=-86T6zooNpA1TN67k25FP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2013-01-07 at 17:15 +0000, Matt Fleming wrote: > On Mon, 2013-01-07 at 02:04 +0000, David Woodhouse wrote: > > On Sun, 2013-01-06 at 00:13 +0000, David Woodhouse wrote: > > > When booting under OVMF we have precisely one GOP device, and it > > > implements the ConOut protocol. > > >=20 > > > We break out of the loop when we look at it... and then promptly abor= t > > > because 'first_gop' never gets set. > >=20 > > Hmmm. I've just fixed OVMF so that when qemu is invoked with the > > '-kernel' argument, it uses the EFI handover protocol. And now graphics > > is broken on kernels *without* this patch. I can't even initialise the > > graphics info in OVMF (as it does for non-EFI handover) because the > > kernel helpfully zeroes it all out before failing to set it up > > correctly. > >=20 > > Does it make sense to bump the boot protocol to 2.12 to indicate that > > this bug is fixed, and then let things like OVMF use the EFI handover > > protocol only for boot protocol >=3D 2.12? Or is there a better way...? >=20 > Bumping the boot protocol seems like a sensible idea. >=20 > Peter, any objection to that? I'd like to fix the 32-bit EFI entry point first. Although the PE entry point helpfully adds 4 to $esp to effectively pop the unwanted return address off the stack, the EFI entry point at 0x30 doesn't. So I'm doing this for now to test OVMF, while I work out why the EFI stub is then crashing in the PCI ROM handling: --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -50,8 +50,10 @@ ENTRY(startup_32) pushl %eax pushl %esi pushl %ecx + pushl %ecx =20 .org 0x30,0x90 + add $0x4, %esp call efi_main cmpl $0, %eax movl %eax, %esi On fact, the whole 32-bit vs 64-bit entry point seems entirely confusing. It seems that a bootloader needs to *know* whether it's loading a 64-bit or a 32-bit kernel image. A quick check shows that grub is always running non-EFI kernels in 32-bit mode, at the 32-bit entry point. So that's fine. But for the EFI stub, a 64-bit grub unconditionally jumps to the undocumented=C2=B9 0x200 + handover_offset, while a 32-bit grub omit= s the 0x200. So if you attempt to boot a 64-bit kernel from a 32-bit grub, or vice versa, it's just going to crash. What is the bootloader *supposed* to do? --=20 dwmw2 =C2=B9 Not strictly true. It's documented as "THIS MAY CHANGE. 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