Backtrace in uClibC

Thomas De Schampheleire patrickdepinguin+uclibc at gmail.com
Mon May 2 14:14:53 UTC 2011


Hi Carmelo,

I tested backtrace on a powerpc system (P4080 family) with
uClibc-0.9.31, and the test program mentioned in the backtrace man
page [1].

The good news is that it seems to work correctly. The raw pointers
returned by backtrace() are correct and complete.
Note that, although the source code of libubacktrace mentions the need
for compiling with '-fexception', it is sufficient to add
'-funwind-tables'. The latter has the advantage of not changing
dynamic behavior (i.e. enabling exception code). I think it would be
good to modify the comment.

Unfortunately, backtrace_symbols() is not yet ok. According to the
expected output of the example I took from [1], static functions
simply have no symbolic resolution in the glibc version; only a
pointer is shown.

However, with the current uClibc / libgcc implementation, a symbolic
name *is* shown for static functions, but it is wrong. Referring to
the example code, the entry referring to myfunc2 is printed as
'myfunc'. If you change the code and make myfunc static and myfunc2
global, then all entries referring to myfunc are printed as 'myfunc2'.
This is problematic in my opinion.

I haven't looked into detail into backtrace_symbols yet. I also don't
know whether the error is in libgcc or libubacktrace. Any thoughts are
appreciated.

Best regards,
Thomas

[1] http://www.kernel.org/doc/man-pages/online/pages/man3/backtrace.3.html


On Tue, Apr 26, 2011 at 2:14 PM, Carmelo AMOROSO <carmelo.amoroso at st.com> wrote:
> On 4/25/2011 10:02 AM, Tony Wu wrote:
>> Hi, Carmelo,
>>
>> If commit 7b5b79f is for generic libubacktrace implementation, then, I
>> think TARGET_sh dependency for UCLIBC_HAS_BACKTRACE should be removed
>> in extra/Configs/Config.in.
>>
>> Tony
>
> You're right. Pushed in master.
>
> Thanks,
> Carmelo
>
>>
>> On Fri, Apr 22, 2011 at 7:06 PM, Carmelo AMOROSO <carmelo.amoroso at st.com> wrote:
>>> On 4/6/2011 8:47 AM, Thomas De Schampheleire wrote:
>>>> Hi Carmelo,
>>>>
>>>> On Tue, Apr 5, 2011 at 7:18 AM, Carmelo AMOROSO <carmelo.amoroso at st.com> wrote:
>>>>> Hello,
>>>>> I'm finally back to work on uClibc. I'm preparing some patches to make
>>>>> backtrace available for all archs, asking you guys to test on your
>>>>> platforms.
>>>>
>>>> I should be able to test it on powerpc.
>>>>
>>>> Looking forward to your patches...
>>>> Thomas
>>>>
>>>
>>> Pushed in master right now. Please let us to know.
>>>
>>> Thanks,
>>> Carmelo
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>
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