Messages in this thread | | | Date | Mon, 2 Oct 2023 11:49:59 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH 0/7] Add support to handle misaligned accesses in S-mode |
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On Mon, Oct 02, 2023 at 09:40:04AM +0200, Clément Léger wrote: > > > 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).
Ah, I must have misread then. Apologies. [unhandled content-type:application/pgp-signature] | |