Ray, The NOP is not a functional change, it's just for ease of debug.
Before, this file was padding with zeros in various places. When viewing this memory using a disassembler, two subsequent zero-bytes show up as an ADD instruction, which I found confusing. But worse, if the number of zero-bytes was odd, the disassembler might try to "consume" part of the next (real) instruction as an operand to the last hypothetical ADD. Since NOP is a 1-byte instruction, I used that instead, so it is easier to visually identify the real code versus the padding when viewing disassembly. -Deric -----Original Message----- From: Ni, Ray <ray...@intel.com> Sent: Monday, June 1, 2020 9:51 PM To: Cole, Deric <deric.c...@intel.com>; devel@edk2.groups.io Cc: Dong, Eric <eric.d...@intel.com>; Laszlo Ersek <ler...@redhat.com> Subject: RE: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector Deric, Can you explain why changing all padding 0x0 to 0x90 (nop) in your patch? Is it required to enable AP start up in pre-mem? Thanks, Ray > -----Original Message----- > From: Cole, Deric <deric.c...@intel.com> > Sent: Tuesday, June 2, 2020 6:32 AM > To: devel@edk2.groups.io > Cc: Cole, Deric <deric.c...@intel.com>; Dong, Eric > <eric.d...@intel.com>; Ni, Ray <ray...@intel.com>; Laszlo Ersek > <ler...@redhat.com> > Subject: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector > > REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2776 > > Add a vector at 0xFF000 (0xFFFFF000) that can be used by > Init-SIPI-SIPI to start an AP before memory is initialized. This > vector jumps into the same SEC entry point as the ordinary reset > vector, with a special value of "AP" in the DI register. The > platform-specific SEC code is expected to check for that value and > take a different path for APs, if this feature is supported by the platform. > > Cc: Eric Dong <eric.d...@intel.com> > Cc: Ray Ni <ray...@intel.com> > Cc: Laszlo Ersek <ler...@redhat.com> > Signed-off-by: Deric Cole <deric.c...@intel.com> > --- > UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb | 31 > ++++++++++++++++++++++++------- > 1 file changed, 24 insertions(+), 7 deletions(-) > > diff --git a/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb > b/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb > index f41b9669d0..1dfc4efe4c 100644 > --- a/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb > +++ b/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb > @@ -10,7 +10,7 @@ > ; Abstract: > > ; > > ; Reset Vector Data structure > > -; This structure is located at 0xFFFFFFC0 > > +; This structure is located at 0xFFFFF000 > > ; > > > ;--------------------------------------------------------------------- > --------- > > > > @@ -23,19 +23,36 @@ USE16 > ; > > > > ORG 0h > > + > > +; > > +; 0xFFFFF000 > > +; > > +; We enter here with CS:IP = 0xFF00:0x0000. Do a far-jump to change > +CS to > 0xF000 > > +; and IP to ApStartup. > > +; > > +ApVector: > > + mov di, "AP" > > + jmp 0xF000:0xF000+ApStartup > > + > > + TIMES 0xFC0-($-$$) nop > > + > > +; > > +; This should be at 0xFFFFFFC0 > > +; > > + > > ; > > ; Reserved > > ; > > ReservedData: DD 0eeeeeeeeh, 0eeeeeeeeh > > > > - TIMES 0x10-($-$$) DB 0 > > + TIMES 0xFD0-($-$$) nop > > ; > > -; This is located at 0xFFFFFFD0h > > +; This is located at 0xFFFFFFD0 > > ; > > mov di, "PA" > > jmp ApStartup > > > > - TIMES 0x20-($-$$) DB 0 > > + TIMES 0xFE0-($-$$) nop > > ; > > ; Pointer to the entry point of the PEI core > > ; It is located at 0xFFFFFFE0, and is fixed up by some build tool > > @@ -53,7 +70,7 @@ ASM_PFX(InterruptHandler): > jmp $ > > iret > > > > - TIMES 0x30-($-$$) DB 0 > > + TIMES 0xFF0-($-$$) nop > > ; > > ; For IA32, the reset vector must be at 0xFFFFFFF0, i.e., 4G-16 byte > > ; Execution starts here upon power-on/platform-reset. > > @@ -74,7 +91,7 @@ ApStartup: > DW -3 > > > > > > - TIMES 0x38-($-$$) DB 0 > > + TIMES 0xFF8-($-$$) nop > > ; > > ; Ap reset vector segment address is at 0xFFFFFFF8 > > ; This will be fixed up by some build tool, > > @@ -83,7 +100,7 @@ ApStartup: > ; > > ApSegAddress: dd 12345678h > > > > - TIMES 0x3c-($-$$) DB 0 > > + TIMES 0xFFC-($-$$) nop > > ; > > ; BFV Base is at 0xFFFFFFFC > > ; This will be fixed up by some build tool, > > -- > 2.26.2.windows.1 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#60604): https://edk2.groups.io/g/devel/message/60604 Mute This Topic: https://groups.io/mt/74621927/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
