[llvm-commits] [llvm] r96569 - in /llvm/trunk: Makefile Makefile.config.in Makefile.rules autoconf/configure.ac configure test/Makefile test/Unit/lit.cfg test/Unit/lit.site.cfg.in tools/llvm-shlib/ unittests/Makefile.unittest

Tue Feb 23 05:27:58 PST 2010

On 2010-02-18 23:56, Xerxes Ranby wrote:
> Jeffrey Yasskin wrote:
>   
>> On Thu, Feb 18, 2010 at 2:53 AM, Xerxes Rånby <xerxes at zafena.se> wrote:
>>   
>>     
>>> Jeffrey Yasskin wrote:
>>>     
>>>       
>>>> Author: jyasskin
>>>> Date: Wed Feb 17 22:43:02 2010
>>>> New Revision: 96569
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=96569&view=rev
>>>> Log:
>>>> Roll back the shared library, r96559.  It broke two darwins and arm, mysteriously.
>>>>
>>>>
>>>>       
>>>>         
>>> Hi
>>> The failure on arm:
>>>
>>> llvm[1]: Linking Debug Shared Library LLVM2.7svn.so
>>> /wd/buildbot/llvm-arm-linux/llvm/Debug/lib/libLLVMSystem.a(Atomic.o): In function `llvm::sys::AtomicAdd(unsigned int volatile*, unsigned int)':
>>> /wd/buildbot/llvm-arm-linux/llvm/lib/System/Atomic.cpp:86: undefined reference to `__sync_add_and_fetch_4'
>>> /wd/buildbot/llvm-arm-linux/llvm/Debug/lib/libLLVMSystem.a(Atomic.o): In function `llvm::sys::AtomicIncrement(unsigned int volatile*)':
>>> /wd/buildbot/llvm-arm-linux/llvm/lib/System/Atomic.cpp:60: undefined reference to `__sync_add_and_fetch_4'
>>> /wd/buildbot/llvm-arm-linux/llvm/Debug/lib/libLLVMSystem.a(Atomic.o): In function `llvm::sys::AtomicDecrement(unsigned int volatile*)':
>>> /wd/buildbot/llvm-arm-linux/llvm/lib/System/Atomic.cpp:73: undefined reference to `__sync_sub_and_fetch_4'
>>> /wd/buildbot/llvm-arm-linux/llvm/Debug/lib/libLLVMSystem.a(Atomic.o): In function `llvm::sys::CompareAndSwap(unsigned int volatile*, unsigned int, unsigned int)':
>>> /wd/buildbot/llvm-arm-linux/llvm/lib/System/Atomic.cpp:47: undefined reference to `__sync_val_compare_and_swap_4'
>>> collect2: ld returned 1 exit status
>>>
>>> I have seen something similar about one year ago when we tried to make
>>> libCompileDriver a shared library:
>>> http://markmail.org/message/cblcpfmsfab65vue
>>>
>>> The issue are that the symbol __sync_add_and_fetch_4 and friends do
>>> exists in libstdc++ but only in the static version.
>>>
>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40133
>>> Quoted Mikael Pettersson from
>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40133#c8
>>> "
>>> 1. g++ links shared libraries with -shared-libgcc, which apparently is
>>> important whenever exceptions are possible.
>>> 2. -shared-libgcc by definition excludes the static libgcc from the link
>>> command.
>>> 3. Since the __sync__ procedures are only present in the static libgcc,
>>> it follows that they cannot be used by -shared-libgcc objects like
>>> libstdc++.so.
>>> "
>>>
>>> A workaround might be to specify -lgcc to force linking in the static
>>> libstdc++ that contains the missing symbols.
>>>
>>> Good news are that it looks like this bug should have been resolved in
>>> gcc trunk.
>>> I will do some tests with r96559 applied on arm to see if this can be
>>> workaround by
>>>
>>> a: make the linking work by specifying -lgcc during linking.
>>> or
>>> b: upgrade gcc and libstdc++ on the buildbot to a newer version.
>>>
>>> Cheers
>>> Xerxes
>>>     
>>>       
>> Thanks for the explanation of the problem! To work around it, I'm
>> going to remove -Wl,--no-undefined from the ARM build. I think the
>> shared library should still find the __sync primitives defined in the
>> main executable, and we'll get assurance that the library is complete
>> from builds on non-ARM platforms.
>>   
>>     
> Test results of workarounds +r96559 on llvm trunk using gcc 4.3.3 on 
> ubuntu arm linux
>
> with removed  --no-undefined from tools/llvm-shlib/Makefile
> the shared library links!
> -rwxr-xr-x 1 xerxes xerxes 21640706 2010-02-18 23:50 
> ../../Release/lib/libLLVM2.7svn.so
> All examples fail to link
> llvm[1]: Linking Release executable BrainF (without symbols)
> /usr/bin/ld: /media/disk/llvm-configure/Release/examples/BrainF: hidden 
> symbol `__sync_val_compare_and_swap_4' in 
> /usr/lib/gcc/arm-linux-gnueabi/4.3.3/libgcc.a(linux-atomic.o) is 
> referenced by DSO
>
> with -lgcc
> LLVMLibsOptions += -lgcc
> the shared library links!
> -rwxr-xr-x 1 xerxes xerxes 21658573 2010-02-18 23:46 
> ../../Release/lib/libLLVM2.7svn.so
> BrainF Fibonacci    Kaleidoscope-Ch2  Kaleidoscope-Ch4  
> Kaleidoscope-Ch6  ModuleMaker
> HowToUseJIT  Kaleidoscope-Ch3  Kaleidoscope-Ch5  Kaleidoscope-Ch7  
> ParallelJIT
> links and run
> ExceptionDemo fails to link
> llvm[1]: ======= Finished Linking Release Executable ParallelJIT 
> (without symbols)
> make[1]: Leaving directory `/media/disk/llvm-configure/examples/ParallelJIT'
> make[1]: Entering directory 
> `/media/disk/llvm-configure/examples/ExceptionDemo'
> llvm[1]: Compiling ExceptionDemo.cpp for Release build
> llvm[1]: Linking Release executable ExceptionDemo (without symbols)
> /media/disk/llvm-configure/examples/ExceptionDemo/Release/ExceptionDemo.o: 
> In function `ourPersonality':
> ExceptionDemo.cpp:(.text+0x60c): undefined reference to `_Unwind_GetIP'
> ExceptionDemo.cpp:(.text+0x7f8): undefined reference to `_Unwind_SetGR'
> ExceptionDemo.cpp:(.text+0x818): undefined reference to `_Unwind_SetGR'
> ExceptionDemo.cpp:(.text+0x828): undefined reference to `_Unwind_SetIP'
> ExceptionDemo.cpp:(.text+0x870): undefined reference to `_Unwind_SetGR'
> collect2: ld returned 1 exit status
> make[1]: *** [/media/disk/llvm-configure/Release/examples/ExceptionDemo] 
> Error 1
> make[1]: Leaving directory 
> `/media/disk/llvm-configure/examples/ExceptionDemo'
> make: *** [ExceptionDemo/.makeall] Error 2
>
> So linking in the static -lgcc makes at least the shared library usable 
> on ARM and only adds 18kb to the shared library size,
> still it needs to be solved how to dynamically link LLVM clients binarys 
> that make use of exceptions.
>   

The example ExceptionDemo got added to llvm two weeks ago and are not
built to work using ARM exception ABI.
Static compilation fails as well as shared compilation so there are
nothing in your changeset that broke this.
The reason why the llvm-arm-linux buildbot dont complain are that
building of llvm examples are disabled on the arm buildbot.
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20100222/096690.html

Cheers
Xerxes

> I will keep you updated if this are all fixed when using a newer gcc and 
> libstdc++ on ARM.
>
> Cheers
> Xerxes
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