[PATCH] arm64: bpf: fix buffer pointer
yang.shi at linaro.org
Wed Nov 18 14:59:17 PST 2015
On 11/18/2015 1:41 PM, Z Lim wrote:
> On Wed, Nov 18, 2015 at 1:07 PM, Shi, Yang <yang.shi at linaro.org> wrote:
>> On 11/18/2015 12:56 AM, Zi Shen Lim wrote:
>>> emit_a64_mov_i64(r3, size, ctx);
>>> - emit(A64_ADD_I(1, r4, fp, MAX_BPF_STACK), ctx);
>>> + emit(A64_SUB_I(1, r4, fp, STACK_SIZE), ctx);
>> Should not it sub MAX_BPF_STACK?
> No, if it's at (BPF_FP - MAX_BPF_STACK), we'll be writing into the BPF
> stack area, which should only be used by the BPF program.
>> If you sub STACK_SIZE here, the buffer pointer will point to bottom of the
>> reserved area.
> Yes, that's the idea. The buffer is allocated in here. Right now we're
> using this "reserved" space for this buffer only.
OK, I see. The buffer grows from low to high.
Thanks for the elaboration.
Acked-by: Yang Shi <yang.shi at linaro.org>
>> You stack layout change also shows this:
>> + * +-----+ <= (BPF_FP - MAX_BPF_STACK)
>> + * |RSVD | JIT scratchpad
>> + * current A64_SP => +-----+ <= (BPF_FP - STACK_SIZE)
> Yes, this diagram reflects the code and intention.
> Thanks for reviewing, we definitely need more of these :)
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