Messages in this thread | | | From | Huacai Chen <> | Date | Mon, 1 Aug 2022 10:34:07 +0800 | Subject | Re: [PATCH v4 0/4] LoongArch: Support new relocation types |
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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?
Huacai > > Thanks, > Youling >
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