Messages in this thread | | | Date | Wed, 14 Mar 2018 10:07:49 -0700 (PDT) | Subject | Re: [PATCH 00/11] RISC-V: Resolve the issue of loadable module on 64-bit | From | Palmer Dabbelt <> |
| |
On Wed, 14 Mar 2018 04:54:14 PDT (-0700), shea@shealevy.com wrote: > Palmer Dabbelt <palmer@sifive.com> writes: > >> On Tue, 13 Mar 2018 18:34:19 PDT (-0700), zongbox@gmail.com wrote: >>> 2018-03-14 5:30 GMT+08:00 Shea Levy <shea@shealevy.com>: >>>> Hi Palmer, >>>> >>>> Palmer Dabbelt <palmer@sifive.com> writes: >>>> >>>>> On Tue, 13 Mar 2018 01:35:05 PDT (-0700), zong@andestech.com wrote: >>>>>> These patches resolve the some issues of loadable module. >>>>>> - symbol out of ranges >>>>>> - unknown relocation types >>>>>> >>>>>> The reference of external variable and function symbols >>>>>> cannot exceed 32-bit offset ranges in kernel module. >>>>>> The module only can work on the 32-bit OS or the 64-bit >>>>>> OS with sv32 virtual addressing. >>>>>> >>>>>> These patches will generate the .got, .got.plt and >>>>>> .plt sections during loading module, let it can refer >>>>>> to the symbol which locate more than 32-bit offset. >>>>>> These sections depend on the relocation types: >>>>>> - R_RISCV_GOT_HI20 >>>>>> - R_RISCV_CALL_PLT >>>>>> >>>>>> These patches also support more relocation types >>>>>> - R_RISCV_CALL >>>>>> - R_RISCV_HI20 >>>>>> - R_RISCV_LO12_I >>>>>> - R_RISCV_LO12_S >>>>>> - R_RISCV_RVC_BRANCH >>>>>> - R_RISCV_RVC_JUMP >>>>>> - R_RISCV_ALIGN >>>>>> - R_RISCV_ADD32 >>>>>> - R_RISCV_SUB32 >>>>>> >>>>>> Zong Li (11): >>>>>> RISC-V: Add sections of PLT and GOT for kernel module >>>>>> RISC-V: Add section of GOT.PLT for kernel module >>>>>> RISC-V: Support GOT_HI20/CALL_PLT relocation type in kernel module >>>>>> RISC-V: Support CALL relocation type in kernel module >>>>>> RISC-V: Support HI20/LO12_I/LO12_S relocation type in kernel module >>>>>> RISC-V: Support RVC_BRANCH/JUMP relocation type in kernel modulewq >>>>>> RISC-V: Support ALIGN relocation type in kernel module >>>>>> RISC-V: Support ADD32 relocation type in kernel module >>>>>> RISC-V: Support SUB32 relocation type in kernel module >>>>>> RISC-V: Enable module support in defconfig >>>>>> RISC-V: Add definition of relocation types >>>>>> >>>>>> arch/riscv/Kconfig | 5 ++ >>>>>> arch/riscv/Makefile | 3 + >>>>>> arch/riscv/configs/defconfig | 2 + >>>>>> arch/riscv/include/asm/module.h | 112 +++++++++++++++++++++++ >>>>>> arch/riscv/include/uapi/asm/elf.h | 24 +++++ >>>>>> arch/riscv/kernel/Makefile | 1 + >>>>>> arch/riscv/kernel/module-sections.c | 156 ++++++++++++++++++++++++++++++++ >>>>>> arch/riscv/kernel/module.c | 175 ++++++++++++++++++++++++++++++++++-- >>>>>> arch/riscv/kernel/module.lds | 8 ++ >>>>>> 9 files changed, 480 insertions(+), 6 deletions(-) >>>>>> create mode 100644 arch/riscv/include/asm/module.h >>>>>> create mode 100644 arch/riscv/kernel/module-sections.c >>>>>> create mode 100644 arch/riscv/kernel/module.lds >>>>> >>>>> This is the second set of patches that turn on modules, and it has the same >>>>> R_RISCV_ALIGN problem as the other one >>>>> >>>>> http://lists.infradead.org/pipermail/linux-riscv/2018-February/000081.html >>>>> >>>>> It looks like this one uses shared libraries for modules instead of static >>>>> objects. I think using shared objects is the right thing to do, as it'll allow >>>>> us to place modules anywhere in the address space by having multiple GOTs and >>>>> PLTs. >>>> >>>> Can you expand on this? It was my understanding that outside of the >>>> context of multiple address spaces sharing code the GOT and PLT were >>>> simply unnecessary overhead, what benefit would they bring here? >>>> >>>>> That's kind of complicated, though, so we can start with something >>>>> simpler like this. >>> >>> Hi, >>> >>> The kernel module is a object file, it is not be linked by linker, the >>> GOT and PLT >>> sections will not be generated through -fPIC option, but it will >>> generate the relative >>> relocation type. As Palmer mention before, If we have GOT and PLT sections, >>> we can put the module anywhere, even we support the KASLR in the kernel. >> >> Sorry, I guess I meant PIC objects not shared objects (I keep forgetting about >> PIE). We'll probably eventually add large code model targets, but they might >> end up just being functionally equilivant to PIE with multi-GOT and multi-PLT >> so it might not matter. >> >> Either way, this is the sanest way to do it for now. >> >>> For the ALIGN problem, the kernel module loader is difficult to remove >>> or migrate >>> the module's code like relax doing, so the remnant nop instructions harm the >>> performance, I agree the point that adding the mno-relax option and checking >>> the alignment in ALIGN type in module loader. >> >> Sounds good. I just merged the mno-relax stuff, it'll show up when I get >> around to generating a 7.3.0 backport branch. For now I think you should just >> fail on R_RISCV_ALIGN and attempt to pass -mno-relax to the compiler (via >> something like "$(call cc-option,-mno-relax)", like we do for >> "-mstrict-align"). I don't think it's worth handling R_RISCV_ALIGN in the >> kernel, as that's essentially the same as full relaxation support. >> > > Should we unconditionally fail on R_RISCV_ALIGN or only if the code > isn't already aligned?
Either way is OK for me. With '-mno-relax' there shouldn't be any R_RISCV_ALIGN relocations, so it shouldn't matter.
>> >>>>> That's kind of complicated, though, so we can start with something >>>>> simpler like this. >>> >>> So what is the suggestion for that. >> >> Well, I'm not really sure -- essentially the idea of proper multi-GOT and >> multi-PLT support would be to merge the GOTs and PLTs of modules together when >> they're within range of each other. We haven't even figured this out in >> userspace yet, so it's probably not worth attempting for kernel modules for a >> bit. >> >> If I understand your code correctly, you're currently generating one GOT and >> one PLT per loaded module. If that's the case, then this is correct, it's just >> possible to save some memory by merging these tables. It's probably not worth >> the complexity for kernel modules for a while.
| |