On Mon, May 9, 2022 at 5:44 PM Qing Zhao <qing.z...@oracle.com> wrote: > > Another question: > > I think that this patch might need to be back ported to Gcc12 and GCC11. > > What’s your opinion on this?
It is not a regression, so following general rules, the patch should not be backported. OTOH, the patch creates functionally equivalent code, better in some security aspects. The functionality is also hidden behind some non-default flag, so I think if release managers (CC'd) are OK with the backport, I'd give it a technical approval. > If so, when can I backport it? Let's keep it in the mainline for a week or two, before backporting it to non-EoL branches. Uros. > > thanks. > > Qing > > > On May 7, 2022, at 4:06 AM, Uros Bizjak <ubiz...@gmail.com> wrote: > > > > On Fri, May 6, 2022 at 6:42 PM Qing Zhao <qing.z...@oracle.com> wrote: > >> > >> > >> > >>> On May 6, 2022, at 10:58 AM, Uros Bizjak <ubiz...@gmail.com> wrote: > >>> > >>> On Fri, May 6, 2022 at 4:29 PM Qing Zhao <qing.z...@oracle.com> wrote: > >>>> > >>>> Hi, > >>>> > >>>> As Kee’s requested in this PR: > >>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101891 > >>>> > >>>> ===== > >>>> > >>>> Currently -fzero-call-used-regs will use a pattern of: > >>>> > >>>> XOR regA,regA > >>>> MOV regA,regB > >>>> MOV regA,regC > >>>> ... > >>>> RET > >>>> > >>>> However, this introduces both a register ordering dependency (e.g. the > >>>> CPU cannot clear regB without clearing regA first), and while greatly > >>>> reduces available ROP gadgets, it does technically leave a set of "MOV" > >>>> ROP gadgets at the end of functions (e.g. "MOV regA,regC; RET"). > >>>> > >>>> Please switch to always using XOR: > >>>> > >>>> XOR regA,regA > >>>> XOR regB,regB > >>>> XOR regC,regC > >>>> ... > >>>> RET > >>>> > >>>> ======= > >>>> > >>>> This patch switch all MOV to XOR on i386. > >>>> > >>>> Bootstrapped and regresstion tested on x86_64-linux-gnu. > >>>> > >>>> Okay for gcc13? > >>>> > >>>> Thanks. > >>>> > >>>> Qing > >>>> > >>>> ========================================== > >>> > >>>> gcc/ChangeLog: > >>>> > >>>> * config/i386/i386.cc (zero_all_mm_registers): Use SET to zero instead > >>>> of MOV for zeroing scratch registers. > >>>> (ix86_zero_call_used_regs): Likewise. > >>>> > >>>> gcc/testsuite/ChangeLog: > >>>> > >>>> * gcc.target/i386/zero-scratch-regs-1.c: Add -fno-stack-protector > >>>> -fno-PIC. > >>>> * gcc.target/i386/zero-scratch-regs-10.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-13.c: Add -msse. > >>>> * gcc.target/i386/zero-scratch-regs-14.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-15.c: Add -fno-stack-protector > >>>> -fno-PIC. > >>>> * gcc.target/i386/zero-scratch-regs-16.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-17.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-18.c: Add -fno-stack-protector > >>>> -fno-PIC, adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-19.c: Add -fno-stack-protector > >>>> -fno-PIC. > >>>> * gcc.target/i386/zero-scratch-regs-2.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-20.c: Add -msse. > >>>> * gcc.target/i386/zero-scratch-regs-21.c: Add -fno-stack-protector > >>>> -fno-PIC, Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-22.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-23.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-26.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-27.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-28.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-3.c: Add -fno-stack-protector. > >>>> * gcc.target/i386/zero-scratch-regs-31.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-4.c: Add -fno-stack-protector > >>>> -fno-PIC. > >>>> * gcc.target/i386/zero-scratch-regs-5.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-6.c: Add -fno-stack-protector. > >>>> * gcc.target/i386/zero-scratch-regs-7.c: Likewise. > >>>> * gcc.target/i386/zero-scratch-regs-8.c: Adjust mov to xor. > >>>> * gcc.target/i386/zero-scratch-regs-9.c: Add -fno-stack-protector. > >>> > >>> Please use something like the attached (functionally equivalent) patch > >>> for the last hunk of your patch. > >> > >> Sure, I will update the code. > >>> > >>> Also, if possible, please use V2SImode as a generic MMX mode instead > >>> of V4HImode. > >> What’s the major purpose of this change? > > > > Although the generated code is the same, V2SI is used as a "generic" > > MMX move insn in the same way V2DI is used to describe generic SSE > > move instruction. > > > > Uros. >
