Re: [PATCH bpf-next 4/4] riscv, bpf: Mixing bpf2bpf and tailcalls

Conor Dooley
2023-09-19T10:05:14Z

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On Tue, Sep 19, 2023 at 11:57:11AM +0800, Pu Lehui wrote:
> From: Pu Lehui <pulehui@huawei.com>
>
> In the current RV64 JIT, if we just don't initialize the TCC in subprog,
> the TCC can be propagated from the parent process to the subprocess, but
> the TCC of the parent process cannot be restored when the subprocess
> exits. Since the RV64 TCC is initialized before saving the callee saved
> registers into the stack, we cannot use the callee saved register to
> pass the TCC, otherwise the original value of the callee saved register
> will be destroyed. So we implemented mixing bpf2bpf and tailcalls
> similar to x86_64, i.e. using a non-callee saved register to transfer
> the TCC between functions, and saving that register to the stack to
> protect the TCC value. At the same time, we also consider the scenario
> of mixing trampoline.
>
> Tests test_bpf.ko and test_verifier have passed, as well as the relative
> testcases of test_progs*.
>
> Signed-off-by: Pu Lehui <pulehui@huawei.com>

Breaks the build:
../arch/riscv/net/bpf_jit_comp64.c:846:14: error: use of undeclared identifier 'BPF_TRAMP_F_TAIL_CALL_CTX'

Thanks,
Conor.

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