[ipxe-devel] 64 bit bARS support.

[Alex Markuze]

Thanks for the prompt answer.
But looking at the download page and your answer it's unclear whether we can compile legacy iPXE (not UEFI) in 64 bit mode.

So the questions is : Can Legacy iPXE work with 64 bit BAR's?

Thanks.

-----Original Message-----
From: Michael Brown [mailto:mbrown at fensystems.co.uk] 
Sent: Friday, May 24, 2013 3:16 PM
To: Alex Markuze
Cc: ipxe-devel at lists.ipxe.org
Subject: Re: [ipxe-devel] 64 bit bARS support.

On 24/05/13 10:54, Alex Markuze wrote:
> I've noticed that the iPXE code has macros and comments regarding the 
> support of 64 bit BAR addresses.
>
> Has this code been ever validated? Does it work or does it still need 
> patching?

The code is working as far as I know.

The special handling for 64-bit BARs is twofold: firstly we need to detect BARs that are 64-bit capable and treat them as such (i.e. treat the next BAR as the high dword rather than being a separate BAR); secondly we need to fail to map 64-bit capable BARs if there's no way for the CPU to access them (i.e. if the BIOS has assigned an address above 4GB and we are running a 32-bit binary).

Most BIOSes should assign addresses below 4GB even for 64-bit capable BARs, to allow for access from within a 32-bit OS.

Under UEFI, the problem goes away since we (usually) run as a 64-bit binary.

Michael