> bpf, riscv: Add BPF stack arguments support for RV64 JIT
>
> Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms
> and kfuncs can receive more than 5 arguments via the stack
> (BPF_REG_PARAMS / r11).
>
> For BPF-to-BPF calls the caller writes outgoing arguments at the
> bottom of its frame (SP-relative). The callee reads them with
> FP-relative loads. Its FP is set to the caller SP in the prologue,
> so the offsets match.
>
> The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at
> SP+0. Before each kfunc call, load arguments 6-8 from the outgoing
> area into A5-A7 and copy any remaining arguments down so argument 9
> lands at SP+0.
>
> A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not
> live before a call, TCC is backed up on the stack, and A7 is unused
> by the JIT.
>
> Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS
> iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and
> corrupts callee-saved registers.
>
> Signed-off-by: Feng Jiang <[email protected]>
This looks like a bug fix for stack argument support. The commit message
describes how the sign-extension loop was limited to prevent corruption
of callee-saved registers S1-S5 when idx >= 5. This fixes an issue
introduced by commit 443574b03387 ("riscv, bpf: Fix kfunc parameters
incompatibility between bpf and riscv abi"), which added the
sign-extension loop without limiting it to MAX_BPF_FUNC_REG_ARGS.
Should this include:
Fixes: 443574b03387 ("riscv, bpf: Fix kfunc parameters incompatibility
between bpf and riscv abi")
---
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See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31677823910
