Messages in this thread | | | From | Huacai Chen <> | Date | Sat, 30 Jul 2022 14:14:59 +0800 | Subject | Re: [PATCH v4 0/4] LoongArch: Support new relocation types |
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Hi, Ruoyao,
On Sat, Jul 30, 2022 at 10:53 AM Xi Ruoyao <xry111@xry111.site> 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. Sadly, I don't know what visibility is, does it have something to do with __visible in include/linux/compiler_attributes.h?
Huacai > > 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 > > -- > Xi Ruoyao <xry111@xry111.site> > School of Aerospace Science and Technology, Xidian University >
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