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Re: [Xen-devel] [PATCH] [Firmware] TCG BIOS extensions for the Bochs BIOS

  • To: Stefan Berger <stefanb@xxxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Mon, 11 Dec 2006 15:43:27 +0000
  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 11 Dec 2006 07:43:32 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AccdOxlpV/dnFIkuEdu9WAAX8io7RQ==
  • Thread-topic: [Xen-devel] [PATCH] [Firmware] TCG BIOS extensions for the Bochs BIOS

I would imagine this working by having generic real-mode/32-bit gateway routines in rombios, and then getting the hell out to 32-bit protected mode asap for new code. The advantages are that you get to code in C, compiled with a modern optimising compiler (gcc), and that you avoid the silly 64kB limitation. As you say, hvmloader would be responsible for poking the routines into high memory, marking them as E820_RESERVED, and then doing some jump-table poking in rombios (which might more generically, and grandiosely, be termed ‘linking’ of the BIOS and its extensions :-).

TBH I’m not happy to check in big gobs of assembly code, or even really bcc C/asm code. We should do the leg work to be able to use gcc. An hvmloader type of environment is what we should aim for --  another way of looking at this is removing hvmloader’s restriction of only running at bootstrap so that it can also provide ongoing run-time services.

 -- Keir

On 11/12/06 15:26, "Stefan Berger" <stefanb@xxxxxxxxxx> wrote:

Someone who wants to add new functionality to the Bochs BIOS might care about the amount of free space in that 64kb segment. Currently there's enough room left even with the TPM extensions.
Even if we move these extensions to some 32bit area, the hook into the 1Ah interrupt and all those other function calls surrounded by #if BX_TCGBIOS in rombios.c are needed as well as later on some code that switches into protected mode and jumps up into the 32 bit area. The BIOS code should at some point be compiled with those TPM extensions independent of whether a TPM is available in the VM or not. The extensions don't influence the BIOS if a TPM is not available.

How would you connect the two code areas and the functions? Would hvmloader write the 32 bit address somewhere into the Bochs BIOS and the to reach the 32 bit area one uses a jump table to call all those functions up there? I'd really rather leave the TPM extensions in the BIOS segment for now. The bulk of the code is located in its own file anyway. I will convert parts of the code to 'C', though.

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