https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101891
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Qing Zhao <qinz...@gcc.gnu.org>: https://gcc.gnu.org/g:0b86943aca51175968e40bbb6f2662dfe3fbfe59 commit r13-213-g0b86943aca51175968e40bbb6f2662dfe3fbfe59 Author: Qing Zhao <qing.z...@oracle.com> Date: Mon May 9 15:34:34 2022 +0000 i386: Adjust -fzero-call-used-regs to always use XOR [PR101891] Currently on i386, -fzero-call-used-regs uses 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"). This patch will switch to always use XOR on i386: XOR regA,regA XOR regB,regB XOR regC,regC ... RET gcc/ChangeLog: PR target/101891 * config/i386/i386.cc (zero_call_used_regno_mode): use V2SImode as a generic MMX mode instead of V4HImode. (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.
