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    SubjectRe: [PATCH v4 0/4] LoongArch: Support new relocation types
    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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