Re: [PATCH] bpftool: fix control flow graph segfault during edge creation

[Quentin Monnet]

On 08/01/2025 22:09, Christoph Werle wrote:
> If the last instruction of a control flow graph building block is a
> BPF_CALL, an incorrect edge with e->dst set to NULL is created and
> results in a segfault during graph output.
> 
> Ensure that BPF_CALL as last instruction of a building block is handled
> correctly and only generates a single edge unlike actual BPF_JUMP*
> instructions.
> 
> Signed-off-by: Christoph Werle <christoph.werle@xxxxxxxxxx>


Fixes: 0824611f9b38 ("tools: bpftool: partition basic-block for each function in the CFG")


> ---
>  tools/bpf/bpftool/cfg.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/bpf/bpftool/cfg.c b/tools/bpf/bpftool/cfg.c
> index eec437cca2ea..e3785f9a697d 100644
> --- a/tools/bpf/bpftool/cfg.c
> +++ b/tools/bpf/bpftool/cfg.c
> @@ -302,6 +302,7 @@ static bool func_add_bb_edges(struct func_node *func)
>  
>  		insn = bb->tail;
>  		if (!is_jmp_insn(insn->code) ||
> +		    BPF_OP(insn->code) == BPF_CALL ||
>  		    BPF_OP(insn->code) == BPF_EXIT) {
>  			e->dst = bb_next(bb);
>  			e->flags |= EDGE_FLAG_FALLTHROUGH;


Thanks for this! It looks OK, would you have a minimal reproducer by any
chance?

Quentin