Re: [PATCH v2 0/8] Fixes for load/store misaligned and access faults

On Fri, Jun 5, 2026 at 7:15 PM Bo Gan <[email protected]> wrote:
>
> Re-visit the load/store misaligned and access fault handlers to fix
> issues related to coding patterns, floating-point state, and instruction
> decoding:
>
>  a. Vector misaligned load/store emulator is invoked improperly
>  b. vsstatus.FS is not set dirty when V=1
>  c. No checking of previous XLEN, resulting in wrong insn decoding
>  d. Load/Store base address is wrongly assumed to be trap address
>  e. High 32-bits of tinst needs to be checked against 0
>
> The pathset is validated on a modified QEMU[1] that exposed misaligned
> faults, and QEMU[2], which further disabled the insn transformation.
> [2] covers more insn decoding branches, including the particular ones
> which can trigger the wrong decoding (c)
>
> The patchset is also validated on Sifive P550 core (ESWIN EIC7700),
> which is RV64-only in M/(V)S/(V)U, no HW misaligned support, no vector,
> and mtinst always 0. Refer to [3] for the git repo/branch that has all
> 6 patches applied along with the test case that exercises all integer
> and floating-point load/store instructions.
>
> Test case used is available in PATCH 8.
>
> There's no change to the behavior of the vector misaligned load/store
> handler. However, I've found additional issues with them:
>
>  - `uint8_t mask[VLEN_MAX / 8]` in sbi_trap_v_ldst.c is 8KB, which
>    can overflow the default 4KB stack.
>  - tinst should be zero'ed out to not confuse previous mode when
>    redirecting faults, otherwise the vector insn can be mistaken
>    as a regular load/store.
>  - VS in previous mode must be set dirty for loads.
>
> These will be addressed in follow-up patches.
>
> [1] https://github.com/ganboing/qemu/tree/ganboing-misalign
> [2] https://github.com/ganboing/qemu/tree/ganboing-misalign-no-tinst
> [3] https://github.com/ganboing/opensbi/tree/fix-ldst-v2
> ---
> Changes in v2:
>  - Addressed Anup's comment for PATCH 5 in v1
>  - Validate load/store offset is 0 in misaligned faults w/ DEBUG build
>
> ---
> Bo Gan (8):
>   include: sbi: Add more mstatus and instruction encoding
>   include: sbi: Add sbi_regs_prev_xlen
>   include: sbi: Add GET_RDS_NUM/SET(_FP32/_FP64)_RDS macros
>   include: sbi: set FS dirty in vsstatus when V=1
>   lib: sbi: Do not override emulator callback for vector load/store
>   Makefile: define OPENSBI_DEBUG if DEBUG builds
>   lib: sbi: Rework load/store emulator instruction decoding
>   [NOT-FOR-UPSTREAM] Test program for misaligned load/store

Applied all patches except last one to the riscv/opensbi repo.

Thanks,
Anup

>
>  Makefile                     |   1 +
>  include/sbi/riscv_encoding.h |  21 +-
>  include/sbi/riscv_fp.h       |  30 ++-
>  include/sbi/sbi_platform.h   |  92 +++++--
>  include/sbi/sbi_trap.h       |  59 ++++
>  include/sbi/sbi_trap_ldst.h  |   4 +-
>  lib/sbi/sbi_trap_ldst.c      | 510 ++++++++++++++++++++++++-----------
>  lib/sbi/sbi_trap_v_ldst.c    |  25 +-
>  tests/ldst.S                 | 134 +++++++++
>  tests/ldst.h                 | 170 ++++++++++++
>  tests/test-misaligned-ldst.c | 154 +++++++++++
>  11 files changed, 994 insertions(+), 206 deletions(-)
>  create mode 100644 tests/ldst.S
>  create mode 100644 tests/ldst.h
>  create mode 100644 tests/test-misaligned-ldst.c
>
> --
> 2.34.1
>
>
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