Re: [PATCH bpf-next 0/2] bpf, riscv: Add support for signed arena loads

On 2026/8/17 15:24, Chen Pei wrote:
> Hi,
> 
> Signed loads from arena memory are currently unsupported on riscv64:
> bpf_jit_supports_insn() rejects BPF_MEMSX loads when in_arena is set,
> so the verifier fails such programs with "sign extending loads from
> arena are not supported yet". The x86 and arm64 JITs gained support
> for them in v6.18 (a91ae3c89311, eab2a71f3a6a). Since compilers are
> free to generate signed loads into arena memory (e.g. GCC-14 was
> reported to do so), otherwise valid BPF programs fail to load on
> riscv64.
> 
> This series adds BPF_PROBE_MEM32SX support to the RV64 JIT and
> enables the corresponding selftests on riscv64:
> 
> 1 implements signed arena loads in the RV64 JIT. The verifier
>    already converts MEMSX loads from PTR_TO_ARENA to
>    BPF_PROBE_MEM32SX once bpf_jit_supports_insn() allows them, so
>    the JIT reuses the existing arena handling: the arena base
>    (RV_REG_ARENA) is added to the source register and the load is
>    emitted with sign extension (lb/lh/lw). BPF_PROBE_MEM32SX is also
>    added to the add_exception_handler() mode gate so faulting loads
>    register an exception table entry that clears the destination
>    register and resumes execution.
> 
> 2 enables the arena LDSX tests on riscv64: JIT disassembly
>    assertions are added to arena_ldsx_disasm, and
>    arena_ldsx_exception/s8/s16/s32 are now run on riscv64.
> 
> The series was verified on riscv64 with QEMU (-M virt -cpu max): all
> five arena_ldsx tests pass, including the exception path (load from
> unallocated arena memory returns 0) and the sign-extension values
> (s8/s16/s32 tests return -1 as expected).
> 
> Note: the __jited assertions in patch 2 were derived from the JIT
> register allocation (R0->a5, R1->a0, R8->s3, R9->s4, arena base in
> s7) and the emit_ldx() code paths; happy to adjust them if a
> disassembler output detail differs.

Test meets happy.

For this series:

Tested-by: Pu Lehui <[email protected]>

> 
> Thanks,
> Pei
> 
> Chen Pei (2):
>    bpf, riscv: Add support for signed arena loads
>    selftests/bpf: Enable arena LDSX tests for riscv64
> 
>   arch/riscv/net/bpf_jit_comp64.c                 | 15 +++++++++------
>   .../testing/selftests/bpf/progs/verifier_ldsx.c | 17 +++++++++++++++++
>   2 files changed, 26 insertions(+), 6 deletions(-)
> 

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