linux-kernel - Re: [PATCH] arm:traps: Don't print stack or raw PC/LR values in backtraces

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Message-ID: <ac712544-e479-26aa-226b-1859517ea60e@huawei.com>
Date:   Mon, 12 Oct 2020 10:23:58 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "Sebastian Andrzej Siewior" <bigeasy@...utronix.de>
CC:     <dima@...sta.com>, <will@...nel.org>, <jpoimboe@...hat.com>,
        <akpm@...ux-foundation.org>, <christian.brauner@...ntu.com>,
        <viro@...iv.linux.org.uk>, <ldufour@...ux.ibm.com>,
        <amanieu@...il.com>, <walken@...gle.com>,
        <ben.dooks@...ethink.co.uk>, <tglx@...utronix.de>,
        <mingo@...nel.org>, <vincent.whitchurch@...s.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wangle6@...wei.com>,
        <luohaizheng@...wei.com>
Subject: Re: [PATCH] arm:traps: Don't print stack or raw PC/LR values in
 backtraces

On 2020/10/12 5:32, Russell King - ARM Linux admin wrote:
> On Fri, Oct 09, 2020 at 10:18:20AM +0200, Sebastian Andrzej Siewior wrote:
>> On 2020-10-09 09:08:50 [+0100], Russell King - ARM Linux admin wrote:
>>> I am really not happy about this - it hurts at least my ability to
>>> debug the kernel when people post oopses to the mailing list. If
>>> people wish to make the kernel harder to debug, and are prepared
>>> to be told "your kernel is undebuggable" then this patch is fine.
>>
>> I haven't look at the patch but don't they keep/add the representation:
>>    PC: symbol+offset/size
>>    LR: symbol+offset/size
>>
>> ? This is needed at very least as a replacement for the missing address.
> 
> I don't have a problem getting rid of the hex numbers in [< >]
> although then I will need to convert the symbol back to an address
> using the vmlinux to then calculate its address to then find the
> appropriate place in the objdump output - because objdump does
> _not_ use the symbol+offset annotation.  Yes, I really do look up
> the numeric addresses in the objdump output to then read the
> disassembly.
> 
> $ objdump -d vmlinux | less
> 
> and then search for the address is the fastest and most convenient
> way for me rather than having to deal with some random script.
> 
> Maybe I'm just antequated about how I do my debugging, but this
> seems to me to be the most efficient and fastest way.
> 
The loading address of the kernel module is not fixed, so symbol+offset 
is more useful than a hexadecimal address when the call stack contains 
kernel module symbols.
Delete the PC/LR address and retain the sysbol+offset. The kernel can 
still be debugged.

Thanks
Xiaoming Ni