Le 02/04/2024 à 12:58, Hari Bathini a écrit :
> With PCREL addressing, there is no kernel TOC. So, it is not setup in
> prologue when PCREL addressing is used. But the number of instructions
> to skip on a tail call was not adjusted accordingly. That resulted in
> not so obvious failures while using tailcalls. 'tailcalls' selftest
> crashed the system with the below call trace:
>
> bpf_test_run+0xe8/0x3cc (unreliable)
> bpf_prog_test_run_skb+0x348/0x778
> __sys_bpf+0xb04/0x2b00
> sys_bpf+0x28/0x38
> system_call_exception+0x168/0x340
> system_call_vectored_common+0x15c/0x2ec
>
> Fixes: 7e3a68be42e1 ("powerpc/64: vmlinux support building with PCREL addresing")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> ---
>
> * Changes in v3:
> - New patch to fix tailcall issues with PCREL addressing.
>
>
> arch/powerpc/net/bpf_jit_comp64.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 79f23974a320..7f62ac4b4e65 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -285,8 +285,10 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
> int b2p_index = bpf_to_ppc(BPF_REG_3);
> int bpf_tailcall_prologue_size = 8;
>
> +#ifndef CONFIG_PPC_KERNEL_PCREL
Any reason for not using IS_ENABLED(CONFIG_PPC_KERNEL_PCREL) ?
> if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
> bpf_tailcall_prologue_size += 4; /* skip past the toc load */
> +#endif
>
> /*
> * if (index >= array->map.max_entries)
