we here use -Werror=unused-but-set-variable gcc compiler option while building our code. Apparently the people using gcc4.5 can build it "even though" there are variables which are set but not used afterwards. But I using gcc4.6 cannot build the code. Is that particular gcc option not implemented in gcc4.5?
thanks in advance
The GCC 4.6 warnings are improved w.r.t. to those produced by GCC 4.5. But you could just use -Wunused-but-set-variable to get warnings, not errors, and more importantly correct your source code (perhaps by removing that useless variable).
Related
I have a cc_library (tbb) that requires the compiler flag -mwaitpkg on some compilers (Clang) to compile successfully. At the same time, there are older versions of GCC (4.9) that do not know this flag, and therefore the compilation via GCC 4.9 leads to an error:
gcc: error: unrecognized command line option '-mwaitpkg'
In a more advanced Bazel setup, I guess one would work around this using hermetic toolchains. This way every toolchain could provide its own set of compiler flags. Nevertheless, I do not want to enforce any specific toolchain and I am not sure if this is the right way to go (move copts to toolchain?).
Also introducing a config would be a way to solve this problem. E.g. bazel build --config=waitpkg //.... But this would require that a user is aware of this config and also knows the details of using waitpkg.
What is a proper "Bazel-way" to handle different compiler flags for different compilers?
The flag '-mwaitpkg' is supported by GCC version 9.3, Clang* 12, and newer versions of those tools.
If you build Bazel with earlier versions of GCC, you should remove the flag otherwise it gives compilation errors.
I am trying to configure the last version of clang (6.0) to use the arm-none-eabi linker instead of the ld.lld but clang is always ignoring everything and keep asking for the ld.lld one. I am trying to build for cortex-m3 (lpx1769 board). How do I force clang to use the linker I want.
-fuse-ld=ld is also not working, so does clang no longer allow the use of any other linker?
So the answer was to use the flag:
-fuse-ld=path/to/linker-to-be-used
Remember that if you passing this flag to clang it will cause a warning that clang will not use this flag (only the linker stage will do). Thus if you compiling with -Werror, the warning will be turned into an error.
Moreover, because you are cross-compiling probably you will need to let the linker know where to find the target-specific libraries needed using the -L option. See this for more info:
https://clang.llvm.org/docs/CrossCompilation.html
I have built clang 3.6 from source and followed the rather straightforward instruction on the page and installed ninja, which I confirmed can build clang-format.
My question is quite simply how to pass some flags so I can get debug symbols because I do not want to do my work (modifying clang-format) using disassembly throughout.
This can be through the standard build (which uses CMake) or ninja.
I've faced similar issue recently (I wanted to debug clang's code itself). Turned out that you need to explicitly specify -DCMAKE_BUILD_TYPE=Debug when you run CMake to generate Ninja or standard makefiles.
BTW, be careful: with this Debug option ld "ate" about 4G of my RAM to link clang binary...
Using MinGW and CMake I've compiled LLVM, Clang and Compiler-RT both via SVN or using the released source code (3.2).
I've modified InitHeaderSearch.cpp (in tools/clang/lib/frontend) to find GCC 4.7.2 headers.
I've set the compile options to Release and disabled assertions.
Clang seems to work properly, but it takes 4-5 seconds to start: even typing "clang --version" in the console does this. Compiling a projects takes a lot of time.
What am I missing? I've used rubenvb's old MinGW+Clang build (GCC 4.6), and it didn't have this problem. Is there any compilation flag I need to use?
This issue is discussed here http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-April/020651.html
AFAIK problem is caused by large relocation table and inefficient MinGW implementation (http://sourceforge.net/p/mingw/bugs/1747/).
Adding -static flag to linker flags should resolve this issue. You should invoke cmake with
-DCMAKE_EXE_LINKER_FLAGS=-static -DCMAKE_MODULE_LINKER_FLAGS=-static
I have build a g++ v4.4 from source by using the archives provided by gcc.gnu.org.
But the resulting g++ cannot compile some of our projects c++ files. I am receiving a message simply saying: assembler error. It turned out that the assembler chokes on some extremely long symbol names, e.g. symbols names with a length of more then 2k.
Am I missing something to get it to work?
I would very appreciate an advice on how to get this working!
Environment: Debian-Lenny 64bit
EDIT: The mentioned c++ files are compiling fine with g++ versions v4.2 and v4.3. So I don't think it is a bug in the assembler (from binutils v2.18). Just to be sure I have also tried with binutils v2.20 - but I got the identical error message.
EDIT: I need g++ v4.4.x for the purpose of comparing the output of different g++ versions (and there is no g++ v4.4 in the official lenny repositories)
If your analysis is correct, it seems the proper course of action would be to file a bug for binutils. Or gcc, if it turns out the long symbol names are due to a bug in gcc's name mangling.
Of course, a (preferably reduced) testcase will help the developers fix your problem. Heck, it could have helped SO readers to verify your problems.
You're going to have to compile the corresponding gas instead of depending on what lenny has in his refrigerator (/usr/bin).
Why don't a) upgrade or b) use the backports archive or c) rebuild from current Debian sources on your box? I happily run testing with g++ 4.2, 4.3 and 4.4.
Worst case, you could install a new Debian release in a virtual environment such as a chroot, a Xen or Kvm instance, or inside VirtualBox.