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@xxxxxxxxxxx>
wrote:
Hi, RuoyaoI don't like such a hack..., can we consider using old relocation
On 07/30/2022 10:52 AM, Xi Ruoyao wrote:
On Sat, 2022-07-30 at 10:24 +0800, Xi Ruoyao wrote:Using the old toolchain (GCC 12) can successfully load the
On Sat, 2022-07-30 at 01:55 +0800, Xi Ruoyao wrote:If addr_global is rejected or not implemented (for example,
On Fri, 2022-07-29 at 20:19 +0800, Youling Tang wrote:Correction: https://github.com/xry111/linux/commit/c1d5d708
On 07/29/2022 07:45 PM, Xi Ruoyao wrote:GCC patch adding "addr_global" attribute for LoongArch:
Hmm... The problem is the "addresses" of per-cpu symbolsYes, we need a GCC attribute to specify the per-cpu
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.
variable.
https://gcc.gnu.org/pipermail/gcc-patches/2022-July/599064.html
An experiment to use it:
https://github.com/xry111/linux/commit/c1d5d70
It seems 7-bit SHA is not enough for kernel repo.
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
nf_tables.ko
module after applying the above patch.
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. :-(