linux-kernel - Re: [PATCH v2 0/5] kallsyms: Emit symbol for holes in text and fix weak function issue

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Message-ID: <20250121124851.2205a8b2@gandalf.local.home>
Date: Tue, 21 Jan 2025 12:48:51 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Zheng Yejian <zhengyejian1@...wei.com>
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Subject: Re: [PATCH v2 0/5] kallsyms: Emit symbol for holes in text and fix
 weak function issue


Sorry for the late reply. Forgot about this as I was focused on other end-of-year issues.

On Sat, 14 Dec 2024 16:37:59 +0800
Zheng Yejian <zhengyejian1@...wei.com> wrote:

> The direct cause of this issue is the wrong fentry being founded by ftrace_location(),
> following the approach of "FTRACE_MCOUNT_MAX_OFFSET", narrowing down the search range
> and re-finding may also solve this problem, demo patch like below (not
> fully tested):
> 
>      diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>      index 9b17efb1a87d..7d34320ca9d1 100644
>      --- a/kernel/trace/ftrace.c
>      +++ b/kernel/trace/ftrace.c
>      @@ -1678,8 +1678,11 @@ unsigned long ftrace_location(unsigned long ip)
>                              goto out;
>      
>                      /* map sym+0 to __fentry__ */
>      -               if (!offset)
>      +               if (!offset) {
>                              loc = ftrace_location_range(ip, ip + size - 1);
>      +                       while (loc > ip && loc - ip > FTRACE_MCOUNT_MAX_OFFSET)
>      +                               loc = ftrace_location_range(ip, loc - 1);
>      +               }
>              }
> 
> Steve, Peter, what do you think?

Hmm, removing the weak functions from the __mcount_loc location should also
solve this, as the ftrace_location_range() will not return a weak function
if it's not part of the __mcount_loc table.

That is, would this patchset work?

  https://lore.kernel.org/all/20250102232609.529842248@goodmis.org/

-- Steve