[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

[Xerxes Rånby]

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