gcc-11 C++ Regression on Cygwin

Jonathan Yong 10walls@gmail.com
Sun May 2 18:44:48 GMT 2021


On 5/2/21 7:10 AM, Liu Hao via Gcc-help wrote:
> 在 2021-05-02 08:02, James McKelvey 写道:
>> My code works fine on Cygwin using C++ 10.2.0. But it fails when I 
>> build with the latest gcc-11 snapshot,gcc-11-20210426, with undefined 
>> references at link time. It fails under -O3 and -O0, with 
>> differenterrors. It failed under earlier snapshots as well.
>>
>>
> 
> We have been aware of this issue since a while ago. I had some 
> discussion with Jonathan Yong (who is notably the Cygwin port 
> maintainer), but there was no conclusion:
> 
> 
> ```
> Apr 01 22:15:51 <lh_mouse>    what's the error?
> Apr 01 22:17:40 <jon_y>    strange I am not able to reproduce it now
> Apr 01 22:17:50 <jon_y>    oh I think I know what the problem was
> Apr 01 22:18:06 <jon_y>    gcc11 was producing broken powf() from the crt
> Apr 01 22:18:23 <jon_y>    for some reason it generated undefined 
> internal compiler symbols
> Apr 01 22:18:28 <jon_y>    like U LC5
> Apr 01 22:18:41 <jon_y>    switching back to gcc-10 fixed it
> Apr 01 22:19:03 <lh_mouse>    that is defined in 'powf.c' I think.
> Apr 01 22:19:13 <jon_y>    and because I did not rebuild 
the crt right 
> after, it must be the reason why the compiler tries to generate its own
> Apr 01 22:19:28 <jon_y>    I mean, there's an inline version in math.h
> Apr 01 22:19:38 <jon_y>    and then another copy in 
> libstdc++-v3/src/c++98/math_stubs_float.cc
> Apr 01 22:19:54 <jon_y>    powf itself is defined
> Apr 01 22:20:04 <jon_y>    but the U LC5 is causing an undefined symbol 
> error
> Apr 01 22:20:19 <jon_y>    I have no idea where this LC5 
should be 
> coming from
> Apr 01 22:20:29 <jon_y>    it only appears in the assembly, not even in 
> the preprocessed file
> Apr 01 22:20:35 <lh_mouse>    so linking failed and configure thought 
> `powf` wasn't available?
> Apr 01 22:21:33 <jon_y>    yes
> Apr 01 22:21:50 <jon_y>    the solution was to revert back to gcc10, 
> rebuild the crt and try again
> 
> ```
> 
> 

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99872 This should already 
be fixed.
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