Messages in this thread | | | Date | Thu, 31 Dec 2015 12:30:42 -0800 | Subject | Re: [PATCHV5 3/3] x86, ras: Add __mcsafe_copy() function to recover from machine checks | From | Tony Luck <> |
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On Wed, Dec 30, 2015 at 3:32 PM, Tony Luck <tony.luck@gmail.com> wrote: > Fifth is just a hack because I clearly didn't understand what I was > doing in parts 2&3 because my new class shows up as '3' not '1'! > > Andy: Can you explain the assembler/linker arithmetic for the class?
Never mind ... figured it out.
The fixup entry in the extable is:
label - . + 0x2000000 - BIAS
The "label - ." part evaluates to a smallish negative value (because the .fixup section is bundled in towards the end of .text, and the ex_table section comes right after.
Then you add 0x20000000 to get a positive number, then *subtract* the BIAS. I'd picked BIAS = 0x40000000 thinking that would show up directly in class bits. But 0x1ffff000 - 0x40000000 is 0xdffff000 so bits 31 & 31 are both set, and this is class3
I switched to BIAS 0xC0000000 ... and now I get class 1 entries (bit31=0, bit30=1).
New patch series coming soon.
-Tony
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