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: <7960f4a0-e45e-7cfd-fa36-97732139d238@huawei.com>
Date: Fri, 7 Feb 2025 11:16:21 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: Steven Rostedt <rostedt@...dmis.org>
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Subject: Re: [PATCH v2 0/5] kallsyms: Emit symbol for holes in text and fix
 weak function issue

On 2025/1/22 01:48, Steven Rostedt wrote:
> 
> 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/

I only pick patch15 and patch16 into v6.14-rc1, since most of patches in that patches
have already merged, and the issue seems gone, thanks!

> 
> -- Steve

-- 
Thanks,
Zheng Yejian