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 (#101400): https://edk2.groups.io/g/devel/message/101400 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] -=-=-=-=-=-=-=-=-=-=-=-
