Hello, Thanks for all the feedbacks and suggestions from everybody! I have sent V3 patch accordingly, please help to review again: https://edk2.groups.io/g/devel/message/101526
Thanks, Chasel > -----Original Message----- > From: Desimone, Nathaniel L <nathaniel.l.desim...@intel.com> > Sent: Tuesday, March 21, 2023 4:05 PM > To: Pedro Falcato <pedro.falc...@gmail.com>; devel@edk2.groups.io; Ni, Ray > <ray...@intel.com> > Cc: Chiu, Chasel <chasel.c...@intel.com>; Zeng, Star <star.z...@intel.com> > Subject: RE: [edk2-devel] [PATCH v2] IntelFsp2Pkg: Fix NASM X64 build > warnings. > > Reviewing this code in more detail... I think clearing the upper 32-bits is a > bug. > These functions are supposed to return pointers, and since this is X64 code > those > pointers could be anywhere in address space. The fact that the FSP is in XIP > NEM, > which on current Intel platforms just happens to be mapped <4GB does not > mean that this pointer will always be 4GB. Therefore, I believe the correct > course of action is to delete the AND/MOV instructions in question. > > Thanks, > Nate > > -----Original Message----- > From: Pedro Falcato <pedro.falc...@gmail.com> > Sent: Monday, March 20, 2023 12:31 AM > To: devel@edk2.groups.io; Ni, Ray <ray...@intel.com> > Cc: Chiu, Chasel <chasel.c...@intel.com>; Desimone, Nathaniel L > <nathaniel.l.desim...@intel.com>; Zeng, Star <star.z...@intel.com> > Subject: Re: [edk2-devel] [PATCH v2] IntelFsp2Pkg: Fix NASM X64 build > warnings. > > On Mon, Mar 20, 2023 at 6:03 AM Ni, Ray <ray...@intel.com> wrote: > > > > > ASM_PFX(FspInfoHeaderRelativeOff): > > > > > > DD 0x12345678 ; This value must be patched by the > > > build script > > > > > > - and rax, 0xffffffff > > > > > > + mov eax, eax ; equal to and rax, 0xFFFFFFFF > > > > Based on the discussion, we know "mov eax, eax" clears upper 32bits of RAX. > > But this code looks very confusing. Is there any other instruction that can > > do > the same thing? > > Hi Ray, > > Any instruction that writes to the lower 32-bits should zero the upper bits. > (Pardon my AT&T syntax, just reverse the operands for Intel syntax) > > and $0xffffffff,%eax gets you a 3 byte opcode (since imm8 is signed, you only > need 0xff as the immediate) and %eax, %eax gets you 2 bytes mov %eax, %eax > gets you 2 bytes > > even something silly like adding 0 to EAX should work. But in a pure > efficiency+size POV, the last 2 instructions should be optimal. > > -- > Pedro -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#101527): https://edk2.groups.io/g/devel/message/101527 Mute This Topic: https://groups.io/mt/97678369/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
