[llvm-dev] Building clang in llvm-3.7 on Linux with RT support enabled

[Alex Wang via llvm-dev]

As far as I know the makefile in there isn't the makefile that gets executed during the cmake build -- cmake generates its own build files from CMakeLists.txt and runs those instead. Having the compiler-rt source in projects/compiler-rt should be enough to have its functionality built into clang when building with cmake.

-Alex

> On Sep 29, 2015, at 11:43 AM, David Lobron via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi All,
> 
> I need to build clang/llvm from source on an Ubuntu Linux system, in order to build the gnustep Objective-C environment.  I was able to build clang using cmake without a problem (following the instructions at clang.llvm.org/get_started.html), but when I tried to build gnustep, I found that clang failed to compile an autoconf-generated program.  The compile error in the configure log was:
> 
> configure:14781: checking for _Block_copy
> configure:14837: clang -o conftest -m64 -march=opteron -mno-3dnow -ggdb -O2 -Wall  -I/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Headers -I/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Headers -I/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Headers  -fgnu-runtime -x objective-c -m64  -L/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Libraries conftest.c -lrt -ldl  -lpthread -rdynamic -m64 -fgnu-runtime -L/home/dlobron/GNUstep/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Libraries -lobjc -lm     >&5
> /tmp/conftest-a47ae0.o: In function `main':
> /home/dlobron/build/clangport/akamai/gnustep-base/gnustep-base-1.24.8/conftest.c:140: undefined reference to `_Block_copy'
> 
> The line in the auto-generated conftest.c that caused the failure is:
> 
> return _Block_copy ();
> 
> I repeated the above command from the command line, and verified that I get the same error.  
> 
> I did some searching of docs and comments, and I it sounds like I need the realtime project to be built.  I did download the llvm/projects/compiler-rt source, but the Makefile in llvm/projects filters it out:
> 
> # Don't build compiler-rt, it isn't designed to be built directly.
> DIRS := $(filter-out compiler-rt,$(DIRS))
> 
> The main source dir of llvm has an LLVM_BUILD_EXTERNAL_COMPILER_RT option, but I wasn't sure if I that would put RT support into clang (which I'd like) or rather, irf it would build a separate RT compiler.
> 
> Can you guys advise me how to build clang on Linux so that _Block_copy will be useable?
> 
> Thank you,
> 
> David
> 
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