Messages in this thread | | | Date | Mon, 2 Oct 2023 09:40:04 +0200 | Subject | Re: [PATCH 0/7] Add support to handle misaligned accesses in S-mode | From | Clément Léger <> |
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On 30/09/2023 11:23, Conor Dooley wrote: > On Tue, Sep 26, 2023 at 05:03:09PM +0200, Clément Léger wrote: >> Since commit 61cadb9 ("Provide new description of misaligned load/store >> behavior compatible with privileged architecture.") in the RISC-V ISA >> manual, it is stated that misaligned load/store might not be supported. >> However, the RISC-V kernel uABI describes that misaligned accesses are >> supported. In order to support that, this series adds support for S-mode >> handling of misaligned accesses as well support for prctl(PR_UNALIGN). >> >> Handling misaligned access in kernel allows for a finer grain control >> of the misaligned accesses behavior, and thanks to the prctl call, can >> allow disabling misaligned access emulation to generate SIGBUS. User >> space can then optimize its software by removing such access based on >> SIGBUS generation. >> >> Currently, this series is useful for people that uses a SBI that does >> not handled misaligned traps. In a near future, this series will make >> use a SBI extension [1] allowing to request delegation of the >> misaligned load/store traps to the S-mode software. This extension has >> been submitted for review to the riscv tech-prs group. An OpenSBI >> implementation for this spec is available at [2]. >> >> This series can be tested using the spike simulator [3] and an openSBI >> version [4] which allows to always delegate misaligned load/store to >> S-mode. > > Some patches in this series do not build for any configs, some are > broken for clang builds and others are broken for nommu. Please try to> build test this more thoroughly before you submit the next version.
Hi Conor,
Thanks for the feedback, I'll check that.
> > Also, AIUI, this series should be marked RFC since the SBI extension > this relies on has not been frozen.
This series does not actually uses the SBI extension but provides a way to detect if misaligned accesses are not handled by hardware nor by the SBI. It has been reported by Ron & Daniel they they have a minimal SBI implementation that does not handle misaligned accesses and that they would like to make use of the PR_SET_UNALIGN feature. This is what this series addresses (and thus does not depend on the mentioned SBI extension).
Thanks,
Clément
> > Cheers, > Conor.
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