Re: [PATCH] tracing/probes: Allow use of BTF names to dereference pointers

[Steven Rostedt]

On Tue, 29 Jul 2025 11:33:35 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> Anonymous structures are also handled:
> 
>   # echo 'e:xmit net.net_dev_xmit +net_device.name(+sk_buff.dev($skbaddr)):string' >> dynamic_events
> 
> Where "+net_device.name(+sk_buff.dev($skbaddr))" is equivalent to:
> 
>   (*(struct net_device *)((*(struct sk_buff *)($skbaddr))->dev)->name)

The above in wrong. It is equivalent to:

  (*(struct net_device *)((*(struct sk_buff *)($skbaddr)).dev).name)

I purposely tried to not use "->" but then failed to do so :-p

> 
> And nested structures can be found by adding more members to the arg:
> 
>   # echo 'f:read filemap_readahead.isra.0 file=+0(+dentry.d_name.name(+file.f_path.dentry($arg2))):string' >> dynamic_events
> 
> The above is equivalent to:
> 
>   *((*(struct dentry *)(*(struct file *)$arg2)->f_path.dentry)->d_name.name)

And this is supposed to be:

   *((*(struct dentry *)(*(struct file *)$arg2).f_path.dentry).d_name.name)

-- Steve