Re: [PATCH v2 2/4] LoongArch: BPF: Move arena register slot below TCC context

[Tiezhu Yang]

On 2026/7/6 下午12:29, bot+bpf-ci@xxxxxxxxxx wrote:
> > LoongArch: BPF: Move arena register slot below TCC context
> >
> > Currently, the stack layout places the optional arena register slot above
> > the tail call counter context. When arena_vm_start is dynamically enabled,
> > it shifts the relative offset of the tcc_ptr slot within the stack frame,
> > causing hardcoded tracking macros to mismatch and potentially leading to
> > memory misalignment or corruption.
> > To fix this, move the arena register save and restore sequences below the
> > tail call counter context slots in both build_prologue() and epilogue. It
> > needs to update __build_epilogue() to insert a proper offset decrement to
> > safely skip the unneeded tcc_ptr reading block while accurately aligning
> > with the relocated arena slot at the very bottom.
> > With this patch, the tcc_ptr slot is always positioned at a fixed distance
> > directly underneath the base callee-saved registers that is independent of
> > whether the arena features are on.
> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
>
> This looks like a fix for a memory misalignment or corruption bug affecting
> arena BPF programs.  Should it carry a Fixes: tag?
>
> The buggy stack layout, where the arena register save/restore and the extra
> stack reservation sit above the tail call counter context, appears to have
> been introduced by:
>
>    Fixes: ef54c517a937 ("LoongArch: BPF: Implement PROBE_MEM32 pseudo instructions")

OK, will add it in v3.

Thanks,
Tiezhu