Re: Possible g++ bug

[hjl at lucon dot org (H.J. Lu)]

> 
> 
> On 17-Apr-99 H.J. Lu wrote:
> >> 
> >> 
> >> 
> >>   H.J.,
> >> 
> >>        I don't have sufficient authority on any
> >>   alphaev56-unknown-linux-gnu system to be able
> >>   to swear this this bug is not due to the local
> >>   environment.  I would be grateful if you would
> >>   make a test for me.
> >> 
> >>   Break the text below into two files, say BugTest.cc
> >>   and BugTestLib.cc
> >> 
> >>   g++ -o BugTest -O0 BugTest.cc BugTestLib.cc
> >> 
> >>   Everything is fine on ix86 and powerpc (32 bits),
> >>   but with egcs-1.1.2, binutils-2.9.1.0.23 and
> >>   libc-2.0.7pre6, on our Linux-Alpha's  => memory leak.
> >>   Current egcs-CVS-mainline does the same thing.
> >> 
> > 
> > Could you please tell me which one you think has
> > memory leak, the compiler or the resulting binary?
> 
>   The resulting binary.
>   ====================
> 
> //---------------------------------------------------------------
> //  BugTestLib.cpp:
> #include <string>
> 
> std::string upcase(const std::string& s)
> {
>    std::string s2(s);
> 
>    for(unsigned int ii = 0; ii < s2.length(); ii++)
>       s2[ii] = toupper(s2[ii]);
> 
>    return s2;
> }
> //---------------------------------------------------------------
> 
>   The s2 handle is not being cleaned up after s2 is processed
>   by the calling routine.
> 
>   The has been some debate about the legality of the code.
>   The opinion of our local "language lawers" is that while
>   returning a pointer would be illegal, we need to return
>   a string.  That should be okay.
> 
>   Still, the difference between Alpha and (ix86 & powerpc)
>   execution is very evident.  When the compiler is able to
>   see both code segments, the is no problem on Alpha either.
> 
>   Thank you for your time.
> 
> 

Hi,

It turned to be an ELF/alpha linker bug. It is in both binutils
2.9.1.0.23 and the gas snapshot 990410. The problem is when there are
2 identical weak symbols in 2 .o files, the ELF/alpha linker doesn't
get rid of one of them. You wind up with 2 symbols referenced from 2 .o
files, instead of one symbol shared by 2 .o files. The ELF/x86 linker
is ok. I hope some will fix the ELF/alpha linker since that bug affects
most if not all C++ codes.

Ian, Richard, I thought the ELF weak symbol handling was not CPU
dependent. I guess I was wrong.

Thanks.


H.J.
----
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