RE: [PATCH v2 07/11] arm64: mops: handle MOPS exceptions

Colton Lewis
2023-05-25T19:51:02Z

> + if (esr & ESR_ELx_MOPS_ISS_MEM_INST) {
> + /* SET* instruction */
> + if (option_a ^ wrong_option) {
> + /* Format is from Option A; forward set */
> + pt_regs_write_reg(regs, dstreg, dst + size);
> + pt_regs_write_reg(regs, sizereg, -size);
> + }
> + } else {
> + /* CPY* instruction */
> + if (!(option_a ^ wrong_option)) {
> + /* Format is from Option B */
> + if (regs->pstate & PSR_N_BIT) {
> + /* Backward copy */
> + pt_regs_write_reg(regs, dstreg, dst - size);
> + pt_regs_write_reg(regs, srcreg, src - size);
> + }
> + } else {
> + /* Format is from Option A */
> + if (size & BIT(63)) {
> + /* Forward copy */
> + pt_regs_write_reg(regs, dstreg, dst + size);
> + pt_regs_write_reg(regs, srcreg, src + size);
> + pt_regs_write_reg(regs, sizereg, -size);
> + }
> + }
> + }

I can see an argument for styling things closely to the ARM manual as
you have done here, but Linux style recommends against deep nesting. In
this case it is unneeded. I believe this can be written as a single
if-else chain and that makes it easier to distinguish the three options.

if ((esr & ESR_ELx_MOPS_ISS_MEM_INST) && (option_a ^ wrong_option)) {
/* Format is from Option A; forward set */
pt_regs_write_reg(regs, dstreg, dst + size);
pt_regs_write_reg(regs, sizereg, -size);
} else if ((option_a ^ wrong_option) && (size & BIT(63)) {
/* Forward copy */
pt_regs_write_reg(regs, dstreg, dst + size);
pt_regs_write_reg(regs, srcreg, src + size);
pt_regs_write_reg(regs, sizereg, -size);
} else if (regs-pstate & PSR_N_BIT) {
/* Backward copy */
pt_regs_write_reg(regs, dstreg, dst - size);
pt_regs_write_reg(regs, srcreg, src - size);
}