Hi,
it's as if different parts of the code thought differently about
PcdDxeIplSwitchToLongMode.
Interpretation #1:
- PcdDxeIplSwitchToLongMode means that we have to *switch* from 32-bit
PEI to 64-bit DXE. Emphasis on "switch", that is, "PEI and DXE have
different bitness".
Interpretation #2:
- PcdDxeIplSwitchToLongMode means that DXE is 64-bit, independently of
PEI bitness.
PcdDxeIplSwitchToLongMode
PEI DXE Interp#1 Interp#2 result
32 32 0 0 OK
32 64 1 1 OK
64 64 0 1 oops
I checked the documentation in MdeModulePkg/MdeModulePkg.dec, and I have
no clue which interpretation it follows.
The picture is further complicated by "PcdDxeIplBuildPageTables" (added
in SVN r12016. It seems to allow one to say (by setting it to FALSE),
"64-bit PEI, 64-bit DXE, but please don't rebuild page tables".
Now, in OVMF, the 32/32 platform DSC file sets PcdDxeIplSwitchToLongMode
to FALSE. No difference between interp#1 and interp#2.
The 32/64 DSC file sets it to TRUE. Detto.
The 64/64 DSC file it to FALSE again, clearly following interp#1 -- "no
switching needed".
Maybe, we should set this PCD to TRUE (ie. follow Interp#2), and turn
off rebuilding the page tables by setting the newer
PcdDxeIplBuildPageTables to FALSE. I have no clue. (We don't use this
second PCD in OVMF, only EmulatorPkg and Nt32Pkg do -- they both set it
to FALSE.)
If OVMF interprets PcdDxeIplSwitchToLongMode differently (==interp#1)
from some other parts of the code (interp#2), well that has not been
causing problems until now, apparently.
But now I'm looking at the S3 suspend/resume code, and it is full of
comments that apparently *equate*
PcdDxeIplSwitchToLongMode==FALSE
with
DXE is 32-bit
Which corresponds to Interp#2.
I'm asking because I'm now reaching the assembly code in
"MdeModulePkg/Universal/Acpi/BootScriptExecutorDxe/X64/S3Asm.S" that
would jump to the (real mode) OSPM waking vector, and it reboots the
machine. I think that maybe the wrong routine is invoked, due to
confusion around PcdDxeIplSwitchToLongMode.
(The reboot happens when LRET pops RIP and CS from the stack. Apparently
the idea behind this exercise is to stay/continue in the same ASM file,
but change the CS. It doesn't work.)
Thanks!
Laszlo
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