Messages in this thread | | | Subject | Re: [PATCH v4 0/4] LoongArch: Support new relocation types | From | Jinyang He <> | Date | Mon, 1 Aug 2022 18:08:45 +0800 |
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On 08/01/2022 05:55 PM, Xi Ruoyao wrote:
> On Mon, 2022-08-01 at 10:34 +0800, Huacai Chen wrote: >> Hi, all, >> >> On Mon, Aug 1, 2022 at 10:16 AM Youling Tang <tangyouling@loongson.cn> >> wrote: >>> Hi, Ruoyao >>> >>> On 07/30/2022 10:52 AM, Xi Ruoyao wrote: >>>> On Sat, 2022-07-30 at 10:24 +0800, Xi Ruoyao wrote: >>>>> On Sat, 2022-07-30 at 01:55 +0800, Xi Ruoyao wrote: >>>>>> On Fri, 2022-07-29 at 20:19 +0800, Youling Tang wrote: >>>>>> >>>>>>> On 07/29/2022 07:45 PM, Xi Ruoyao wrote: >>>>>>>> Hmm... The problem is the "addresses" of per-cpu symbols >>>>>>>> are >>>>>>>> faked: they >>>>>>>> are actually offsets from $r21. So we can't just load >>>>>>>> such an >>>>>>>> offset >>>>>>>> with PCALA addressing. >>>>>>>> >>>>>>>> It looks like we'll need to introduce an attribute for GCC >>>>>>>> to >>>>>>>> make >>>>>>>> an >>>>>>>> variable "must be addressed via GOT", and add the >>>>>>>> attribute into >>>>>>>> PER_CPU_ATTRIBUTES. >>>>>>> Yes, we need a GCC attribute to specify the per-cpu >>>>>>> variable. >>>>>> GCC patch adding "addr_global" attribute for LoongArch: >>>>>> https://gcc.gnu.org/pipermail/gcc-patches/2022-July/599064.html >>>>>> >>>>>> An experiment to use it: >>>>>> https://github.com/xry111/linux/commit/c1d5d70 >>>>> Correction: https://github.com/xry111/linux/commit/c1d5d708 >>>>> >>>>> It seems 7-bit SHA is not enough for kernel repo. >>>> If addr_global is rejected or not implemented (for example, >>>> building the >>>> kernel with GCC 12), *I expect* the following hack to work (I've >>>> not >>>> tested it because I'm AFK now). Using visibility in kernel seems >>>> strange, but I think it may make some sense because the modules >>>> are some >>>> sort of similar to an ELF shared object being dlopen()'ed, and our >>>> way >>>> to inject per-CPU symbols is analog to ELF interposition. >>>> >>>> arch/loongarch/include/asm/percpu.h: >>>> >>>> #if !__has_attribute(__addr_global__) && defined(MODULE) >>>> /* Magically remove "static" for per-CPU variables. */ >>>> # define ARCH_NEEDS_WEAK_PER_CPU >>>> /* Force GOT-relocation for per-CPU variables. */ >>>> # define PER_CPU_ATTRIBUTES >>>> __attribute__((__visibility__("default"))) >>>> #endif >>>> >>>> arch/loongarch/Makefile: >>>> >>>> # Hack for per-CPU variables, see PER_CPU_ATTRIBUTES in >>>> # include/asm/percpu.h >>>> if (call gcc-does-not-support-addr-global) >>>> KBUILD_CFLAGS_MODULE += -fPIC -fvisibility=hidden >>>> endif >>>> >>> Using the old toolchain (GCC 12) can successfully load the >>> nf_tables.ko >>> module after applying the above patch. >> I don't like such a hack..., can we consider using old relocation >> types when building by old toolchains? > > I don't like the hack too. I only developed it as an intellectual game. > > We need to consider multiple combinations: > > (1) Old GCC + old Binutils. We need -mla-local-with-abs for > KBUILD_CFLAGS_MODULE. > > (2) Old GCC + new Binutils. We need -mla-local-with-abs for > KBUILD_CFLAGS_MODULE, *and* adding the support for > R_LARCH_ABS{_HI20,_LO12,64_LO20,64_HI12} in the kernel module loader. > > (3) New GCC + old Binutils. As new GCC should support our new attribute > (I now intend to send V2 patch to gcc-patches using "movable" as the > attribute name), no special action is needed. > > Basically, we need: > > (1) Handle R_LARCH_ABS{_HI20,_LO12,64_LO20,64_HI12} in the kernel module > loader. > (2) Add -Wa,-mla-local-with-abs into KBUILD_CFLAGS_MODULE if GCC version > is <= 12.
Actually, I really hope kernel image is in the XKVRANGE, rather than being in XKPRANGE. So that we can limit kernel and modules be in 4GB range. I think it will make all work normally. :-(
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