On Mon, 2023-02-06 at 21:13 +0800, Jianmin Lv wrote: > > (1) Is the difference contributed by a bad code generation of GCC? If > > true, it's better to improve GCC before someone starts to build a distro > > for LA264 as it would benefit the user space as well. > > > AFAIK, GCC builds to produce unaligned-access-enabled target binary by > default (without -mstrict-align) for improving user space performance > (small size and runtime high performance), which is also based the fact > that the vast majority of LoongArch CPUs support unaligned-access. I mean: if someone starts to build a distro for a less-capable LoongArch processor, (s)he will need an entire user space compiled with -mstrict- align. So it would be better to start preparation now. And it's likely (s)he will either submit a GCC patch to make GCC enable/disable -mstrict-align based on the -march= (--with-arch at configure time) value, or hack GCC to enable -mstrict-align by default for the distro. So I think we'll also need: > +ifdef CONFIG_ARCH_STRICT_ALIGN may enable strict align by default. > # Don't emit unaligned accesses. > # Not all LoongArch cores support unaligned access, and as kernel we can't > # rely on others to provide emulation for these accesses. > KBUILD_CFLAGS += $(call cc-option,-mstrict-align) +else +# Distros designed for running on both kind of processors may disable +# strict align by default, but the user may want a no-strict-align +# kernel for his/her specific hardware. KBUILD_CFLAGS += $(call cc-option,-mno-strict-align) > +endif -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
