[0/7] Zbb string optimizations and call support in alternatives

Message

Heiko Stübner Nov. 10, 2022, 4:49 p.m. UTC

From: Heiko Stuebner <[e-mail]>

The Zbb extension can be used to make string functions run a lot
faster.

To allow There are essentially two problems to solve:
- making it possible for str* functions to replace what they do
  in a performant way

  This is done by inlining the core functions and then
  using alternatives to call the actual variant.

  This of course will need a more intelligent selection mechanism
  down the road when more variants may exist using different
  available extensions.

- actually allowing calls in alternatives
  Function calls use auipc + jalr to reach those 32bit relative
  addresses but when they're compiled the offset will be wrong
  as alternatives live in a different section. So when the patch
  gets applied the address will point to the wrong location.

  So similar to arm64 the target addresses need to be updated.

  This is probably also helpful for other things needing more
  complex code in alternatives.


In my half-scientific test-case of running the functions in question
on a 95 character string in a loop of 10000 iterations, the Zbb
variants shave off around 2/3 of the original runtime.


changes since rfc:
- make Zbb code actually work
- drop some unneeded patches
- a lot of cleanups


Heiko Stuebner (7):
  efi/riscv: libstub: mark when compiling libstub
  RISC-V: add auipc elements to parse_asm header
  RISC-V: add U-type imm parsing to parse_asm header
  RISC-V: add rd reg parsing to parse_asm header
  RISC-V: fix auipc-jalr addresses in patched alternatives
  RISC-V: add infrastructure to allow different str* implementations
  RISC-V: add zbb support to string functions

 arch/riscv/Kconfig                    |  23 ++++++
 arch/riscv/include/asm/errata_list.h  |   3 +-
 arch/riscv/include/asm/hwcap.h        |   1 +
 arch/riscv/include/asm/parse_asm.h    |  21 +++++
 arch/riscv/include/asm/string.h       |  83 ++++++++++++++++++++
 arch/riscv/kernel/cpu.c               |   1 +
 arch/riscv/kernel/cpufeature.c        |  97 ++++++++++++++++++++++-
 arch/riscv/kernel/image-vars.h        |   6 +-
 arch/riscv/lib/Makefile               |   6 ++
 arch/riscv/lib/strcmp.S               |  39 ++++++++++
 arch/riscv/lib/strcmp_zbb.S           |  91 ++++++++++++++++++++++
 arch/riscv/lib/strlen.S               |  29 +++++++
 arch/riscv/lib/strlen_zbb.S           |  98 ++++++++++++++++++++++++
 arch/riscv/lib/strncmp.S              |  41 ++++++++++
 arch/riscv/lib/strncmp_zbb.S          | 106 ++++++++++++++++++++++++++
 drivers/firmware/efi/libstub/Makefile |   2 +-
 16 files changed, 640 insertions(+), 7 deletions(-)
 create mode 100644 arch/riscv/lib/strcmp.S
 create mode 100644 arch/riscv/lib/strcmp_zbb.S
 create mode 100644 arch/riscv/lib/strlen.S
 create mode 100644 arch/riscv/lib/strlen_zbb.S
 create mode 100644 arch/riscv/lib/strncmp.S
 create mode 100644 arch/riscv/lib/strncmp_zbb.S