Re: [PATCH v3 2/3] tracing/probes: Fix BTF kflag check for anonymous struct member access

[Steven Rostedt <rostedt@goodmis.org>]

On Tue,  1 Sep 2026 23:21:49 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> btf_find_struct_member() traverses into nested anonymous structures and
> unions to find a struct member. However, get_bitoffset_of_field() in
> trace_probe.c checked btf_type_kflag(type) using the outer parent type
> instead of the actual anonymous structure/union that directly contains
> the found member.
> 
> If the parent structure and anonymous structure have mismatched kflags
> (e.g., the parent has kflag=0 while the anonymous structure has kflag=1
> because it contains bitfields), the bitfield size encoded in the upper
> 8 bits of member->offset is erroneously treated as part of the byte/bit
> offset, corrupting the resolved offset and failing to set last_bitsize.
> Similarly, btf_find_struct_member() pushed anonymous member offsets
> onto anon_stack without masking BTF_MEMBER_BIT_OFFSET() when kflag is set.
> 
> To fix this problem, update btf_find_struct_member() to return actual
> containing structure/union type via member_type, use appropriate
> __btf_member_bit_offset() to get bit offset, and use member_type for
> btf_type_kflag() in get_bitoffset_of_field().
> 
> Fixes: c440adfbe302 ("tracing/probes: Support BTF based data structure field access")
> Cc: stable@vger.kernel.org
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/all/20260822095110.0772E1F000E9@smtp.kernel.org/
> Assisted-by: Antigravity:gemini-3.7-flash
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve