Re: undefined reference to __gxx_personality_v0

[Richard Henderson <rth at twiddle dot net>]

On 2012-06-18 09:47, Chris Metcalf wrote:
> On 6/18/2012 12:38 PM, Richard Henderson wrote:
>> On 2012-06-18 00:55, Andreas Jaeger wrote:
>>> are you suggesting that GCC 4.7 (the compiler I use) is doing a better 
>>> job at optimization than GCC 4.4 (Roland's and Chris' version)?
>>>
>>> Btw. the test case was introduced in May 2011 and I never saw it 
>>> failing,
>>
>> I have no idea what the actual subject is; there didn't seem to be a
>> proper referant in roland's original post.  I merely answered the 
>> question of what dw2_force_const_mem does.
> 
> I started this thread here:
> 
> http://sourceware.org/ml/libc-alpha/2012-06/msg00430.html

Ah, right.  I've now done some actual digging into the sources and
have reproduced the problem.

So, I had mis-remembered what dw2_force_const_mem was for.  In this
case, the putting the dynamic relocation for the personality function
in a section other than the unwind info.

You can see this still in current gcc via any test case that needs
to run an exception handling cleanup.  E.g. -fPIC

	struct S { S(); ~S(); };
	void bar();
	void foo() { S s; bar(); }

Now, there's nothing about in_lib that ought to be generating a 
cleanup, however in gcc 4.4 we did not yet have an optimization
that would elide the personality routine when it was unneeded.
That was done in gcc 4.5 as a part of supporting multiple 
simultaneous personalites during LTO.


r~