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:

These patches also support more relocation types

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


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

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

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).

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