From: Andrew Morton <akpm@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org
Subject: Re: [PATCH v3] ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak functions
Date: Thu, 26 May 2022 10:05:30 -0700 [thread overview]
Message-ID: <20220526100530.6ef0a17084f6abab77d8b2ba@linux-foundation.org> (raw)
In-Reply-To: <20220526103810.026560dd@gandalf.local.home>
On Thu, 26 May 2022 10:38:10 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> If an unused weak function was traced, it's call to fentry will still
> exist, which gets added into the __mcount_loc table. Ftrace will use
> kallsyms to retrieve the name for each location in __mcount_loc to display
> it in the available_filter_functions and used to enable functions via the
> name matching in set_ftrace_filter/notrace. Enabling these functions do
> nothing but enable an unused call to ftrace_caller. If a traced weak
> function is overridden, the symbol of the function would be used for it,
> which will either created duplicate names, or if the previous function was
> not traced, it would be incorrectly listed in available_filter_functions
> as a function that can be traced.
This might be dependent on binutils version. In some situations the
unused __weak function might be dropped altogether. This change
(https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1)
tripped up recordmcount
(https://lore.kernel.org/all/20220518181828.645877-1-naveen.n.rao@linux.vnet.ibm.com/T/#u).
The kexec fix will be to just give up on using __weak.
next prev parent reply other threads:[~2022-05-26 17:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-26 14:38 [PATCH v3] ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak functions Steven Rostedt
2022-05-26 14:44 ` Steven Rostedt
2022-05-26 17:05 ` Andrew Morton [this message]
2022-05-26 18:02 ` Steven Rostedt
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