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

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Date:   Fri, 9 Oct 2020 16:58:42 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Russell King - ARM Linux admin" <linux@...linux.org.uk>
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 2020/10/9 16:18, 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

In the reset scenario, dump_mem is retained:

@@ -125,6 +118,9 @@ static void dump_mem(const char *lvl, const char 
*str, unsigned long bottom,
         mm_segment_t fs;
         int i;

+ /* Do not print virtual addresses in non-reset scenarios */
+ if (!panic_on_oops)
+         return;


>> 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.

Yes, only %08lx was deleted, but %ps is still retained.

-	printk("%s[<%08lx>] (%ps) from [<%08lx>] (%pS)\n",
-		loglvl, where, (void *)where, from, (void *)from);
+	printk("%s (%ps) from (%pS)\n",
+		loglvl, (void *)where, (void *)from);

Thanks
Xiaoming Ni