* Marek Majkowski <ma...@cloudflare.com> wrote:
> "%pB" is intended for return addresses, and actually resolves the
> address - 1. So it should only be used for backtraces. Plain
> instruction addresses should use "%pS", which resolves the given
> address.
>
> show_regs was using "%pB" to resolve the RIP symbol. This resolved the
> wrong symbol if the first instruction after a symbol created the
> OOPS/BUG. For example:
>
> 0000000000000049 <before>:
> 49: 90 nop
> 4a: 90 nop
> 4b: 90 nop
> 4c: 90 nop
> 000000000000004d <suicide>:
> 4d: ff 14 25 00 00 00 00 callq *0x0
> 54: c3 retq
>
> Will produce a message saying it's "before" that crashed, not "suicide".
>
> This problem only happens when the crash occurs in the first instruction
> after a symbol. Therefore it's unlikely to occur on kernels with frame
> pointers (CONFIG_FRAME_POINTER=y).
>
> Signed-off-by: Marek Majkowski <ma...@cloudflare.com>
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index deb6421..4c90013 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -27,6 +27,12 @@ static int die_counter;
>
> void printk_address(unsigned long address, int reliable)
> {
> + pr_cont(" [<%p>] %s%pS\n",
> + (void *)address, reliable ? "" : "? ", (void *)address);
> +}
> +
> +static void printk_trace_address(unsigned long address, int reliable)
> +{
> pr_cont(" [<%p>] %s%pB\n",
> (void *)address, reliable ? "" : "? ", (void *)address);
> }
> @@ -151,7 +157,7 @@ static void print_trace_address(void *data, unsigned long
> addr, int reliable)
> {
> touch_nmi_watchdog();
> printk(data);
> - printk_address(addr, reliable);
> + printk_trace_address(addr, reliable);
> }
>
> static const struct stacktrace_ops print_trace_ops = {
There's a recent commit from Jiri Slaby that I think tries to address the
same problem:
8d4c812a3e5f x86/dumpstack: Fix printk_address for direct addresses
You can find it in the -tip tree:
git remote add tip git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
Thanks,
Ingo
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