Re: Out of order unwind entry warning

[Helge Deller <deller@gmx.de>]

On 10/28/2009 12:19 AM, John David Anglin wrote:
>>
>> I started to look into the problem why we get the
>>> WARNING: Out of order unwind entry!
>> warning messages at kernel bootup in dmesg.
>>
>> It's related to a binutils/linker bug, that ld does not correctly
>> removes unlink information for unused weak symbols, which have been
>> replaced by their non-weak ones.
>>
>> In my kernel I could track it down to 2 symbols:
>> - arch_mod_section_prepend()  from kernel/module.c, and
>> - save_stack_trace_tsk().
>>
>> Here is the extract of the readelf output on vmlinux:
>> ...
>> <inb>: [0x1011fbd4-0x1011fc48]
>>           Entry_GR=1 Save_SP Save_RP Total_frame_size=8
>> <arch_mod_section_prepend>: [0x1011fc4c-0x1011fc74]
>>           Entry_GR=1 Save_SP Total_frame_size=8
>> <arch_mod_section_prepend>: [0x1011fc4c-0x10167cf4]
>>           Entry_GR=1 Save_SP Total_frame_size=8
>> <module_arch_cleanup>: [0x1011fc78-0x1011fcb8]
>>           Entry_GR=2 Save_SP Save_RP Total_frame_size=8
>> ...
>
> It might be useful to know the actual location arch_mod_section_prepend
> and whether it follows inb in its .o.  From my understanding of things,
> it shouldn't be necessary to remove the unwind info for unused weak
> symbols if they aren't garbage collected.  A simple testcase would
> be helpful.

arch_mod_section_prepend() is here:
* arch/parisc/kernel/module.c  - non-weak function
* kernel/module.c - weak function

inb() is not defined in arch/parisc/kernel/module.c.
But during kernel build, all object files in arch/parisc/kernel/*.o are
linked together into arch/parisc/kernel/built-in.o:

Running readelf: "hppa-linux-readelf -u arch/parisc/kernel/built-in.o" gives:
...
<inb>: [0x0-0xe8]
         Entry_GR=1 Save_SP Save_RP Total_frame_size=8
<arch_mod_section_prepend>: [0x0-0x50]
         Entry_GR=1 Save_SP Total_frame_size=8
<module_arch_cleanup>: [0x0-0x80]
         Entry_GR=2 Save_SP Save_RP Total_frame_size=8

So, yes, the non-weak arch_mod_section_prepend() function follows the inb()
function in the object file (and in the final vmlinux file as well).

>> <arch_mod_section_prepend>: [0x1011fc4c-0x1011fc74]
>>           Entry_GR=1 Save_SP Total_frame_size=8
>> <arch_mod_section_prepend>: [0x1011fc4c-0x10167cf4]
>>           Entry_GR=1 Save_SP Total_frame_size=8

The first entry is the non-weak one.
The second entry is the remaining part of the weak (dropped) function.
It seems only the start address was changed to the start address of the non-weak
function, while the end address has been kept unchanged.
[0x1011fc4c-0x10167cf4] would mean, that the weak function would be 295KB in size...?

Helge