From: H. Peter Anvin on
On 06/24/2010 12:01 PM, Josh Triplett wrote:
> On Thu, Jun 24, 2010 at 07:18:34AM -0700, H. Peter Anvin wrote:
>> On 06/24/2010 12:27 AM, Josh Triplett wrote:
>>> The following patch fixes GRUB; with this patch, I can reserve memory
>>> (such as with drivemap), boot 2.6.35-rc3 successfully, and it detects
>>> all of my RAM.
>> Congratulations! You have just committed the single most common BIOS
>> implementation bug. (Sorry for the sarcasm, but this seems to be a bug
>> that almost everyone who tries to implement BIOS makes at one point or
>> another... even the original IBM BIOS had it in at least one place.)
> And a rather large number of sample interrupt code found on the web,
> including the e820 hook from the version of gPXE/Etherboot that I used
> as an example. :) Given that I just tested against Linux, which very
> carefully works around that particular BIOS bug, I didn't run into any
> issue.
> So, how high does GRUB's bug ("stc ; iret"/"clc ; iret") rank on the
> list of common BIOS implementation bugs?

Less common, since that one is apparently more obvious to people (you
only have to think one step ahead instead of two steps ahead.)

There is a reason Linux works around this and similar bugs... it truly
is extremely common (and does cause real problems in real code.)


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