Palmer Dabbelt <pal...@sifive.com> writes: > On Wed, 14 Mar 2018 05:07:09 PDT (-0700), s...@shealevy.com wrote: >> Palmer Dabbelt <pal...@sifive.com> writes: >> >>> On Tue, 13 Mar 2018 14:30:53 PDT (-0700), s...@shealevy.com wrote: >>>> Hi Palmer, >>>> >>>> Palmer Dabbelt <pal...@sifive.com> writes: >>>> >>>>> On Tue, 13 Mar 2018 01:35:05 PDT (-0700), z...@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? >>> >>> We don't currently have any position-dependent RISC-V code models larger >>> than >>> "medany", in which all code and data must live within a single 32-bit >>> addressable range. The PLT and GOT sort of provide an out here, so the code >>> only needs to get to the table (which can then get anywhere via an >>> indirection >>> layer). >>> >>> This is relevant for Linux modules because it lets us load modules anywhere >>> in >>> the address space. It's also a bit of a headache, as it either requires a >>> GOT+PLT per module (which is big) or merging tables (which is hard). >> >> I see, thanks! We only get this benefit if we actually do the relevanat >> indirection in the table, right? And if we merge tables we still have to >> have all modules within 32 bits of the common table? Is this how some >> future "medlarge" code model will work, or is it more of a convenient >> way to reuse existing techniques until other code models are worked out? > > The idea is that you'd merge the tables only when it's possible to do that > correctly, which is the tricky part. > > It'd be called "largeany", the "med" part is what limits the code model to 32 > bit offsets. We might just call it "large", as the "any" is kind of > redundant.
Ah, right, that makes more sense :D. So would "mcmodel=large" also use PLTs/GOTs for long jumps?
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