Re: [PATCHv3 bpf-next 1/3] bpf: Add support for bpf_get_func_ip helper for uprobe program

[Yonghong Song <yonghong.song@linux.dev>]

On 8/7/23 1:59 AM, Jiri Olsa wrote:
> Adding support for bpf_get_func_ip helper for uprobe program to return
> probed address for both uprobe and return uprobe.
> 
> We discussed this in [1] and agreed that uprobe can have special use
> of bpf_get_func_ip helper that differs from kprobe.
> 
> The kprobe bpf_get_func_ip returns:
>    - address of the function if probe is attach on function entry
>      for both kprobe and return kprobe
>    - 0 if the probe is not attach on function entry
> 
> The uprobe bpf_get_func_ip returns:
>    - address of the probe for both uprobe and return uprobe
> 
> The reason for this semantic change is that kernel can't really tell
> if the probe user space address is function entry.
> 
> The uprobe program is actually kprobe type program attached as uprobe.
> One of the consequences of this design is that uprobes do not have its
> own set of helpers, but share them with kprobes.
> 
> As we need different functionality for bpf_get_func_ip helper for uprobe,
> I'm adding the bool value to the bpf_trace_run_ctx, so the helper can
> detect that it's executed in uprobe context and call specific code.
> 
> The is_uprobe bool is set as true in bpf_prog_run_array_sleepable, which
> is currently used only for executing bpf programs in uprobe.
> 
> Renaming bpf_prog_run_array_sleepable to bpf_prog_run_array_uprobe
> to address that it's only used for uprobes and that it sets the
> run_ctx.is_uprobe as suggested by Yafang Shao.
> 
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Tested-by: Alan Maguire <alan.maguire@oracle.com>
> [1] https://lore.kernel.org/bpf/CAEf4BzZ=xLVkG5eurEuvLU79wAMtwho7ReR+XJAgwhFF4M-7Cg@mail.gmail.com/
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Acked-by: Yonghong Song <yonghong.song@linux.dev>