On 2011-09-26 19:22, Blue Swirl wrote: > On Mon, Sep 26, 2011 at 11:56 AM, Peter Maydell > <peter.mayd...@linaro.org> wrote: >> On 26 September 2011 12:43, Jan Kiszka <jan.kis...@siemens.com> wrote: >>> On 2011-09-26 13:33, Peter Maydell wrote: >>>> On 26 September 2011 11:51, Jan Kiszka <jan.kis...@siemens.com> wrote: >>>>> This increases the overhead of frequently executed helpers. We need to >>>>> move rule past QEMU_CFLAGS assignment to ensure that the required simple >>>>> assignment picks up all bits. The signal workaround is moved just for >>>>> the sake of consistency. >>>> >>>>> +# NOTE: Must be after the last QEMU_CFLAGS assignment >>>>> +op_helper.o user-exec.o: QEMU_CFLAGS := $(subst >>>>> -fstack-protector-all,,$(QEMU_CFLAGS)) $(HELPER_CFLAGS) >>>> >>>> Why also user-exec.o ? >>> >>> That's a good question. It doesn't look like it's deserving this. >>> >>>> Why not the other source files with helpers in? >>> >>> Name them and I add them. >> >> target-*/*helper.c ? >> >> But mostly I think what I'm trying to say is that this is making >> a tradeoff between safety and speed, so it ought to come with a >> rationale for why it is OK to remove the safety checks for these >> files. Given that rationale you can identify other files that are >> also safe/worthwhile to flip the flag for. > > I wouldn't remove -fstack-protector-all by default. Especially op code > interfaces with the guest.
I'd love to have some function attribute for this, because a stack protector for rather simple arithmetic operations or something like helper_cli/sti are pointlessly burned cycles. Maybe we can introduce op_helper_simple.c. > > For max performance version, I'd check if -fomit-frame-pointer and -O3 > makes sense. See also this article: > https://www.debian-administration.org/article/672/Optimizing_code_via_compiler_flags We already run without frame pointers, -O3 might be worth exploring in addition. Still, that won't take the protector overhead away. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux