Weird flags when building LLVM project with Make using the Clang Compiler - c

Question

I recently built LLVM into the following path: C:\LLVM\llvm-new-build. I then added this path to my Environmental Variables/Path, C:\LLVM\llvm-new-build\Debug\bin. I'm trying to build my LLVM project, but I'm getting some weird output from Clang:
clang `llvm-config --cflags` -Wall -Iincludes/ src/*.c -c src/*.c
clang.exe: error: unknown argument: '-wd4146'
clang.exe: error: unknown argument: '-wd4180'
clang.exe: error: unknown argument: '-wd4244'
clang.exe: error: unknown argument: '-wd4258'
clang.exe: error: unknown argument: '-wd4267'
clang.exe: error: unknown argument: '-wd4291'
clang.exe: error: unknown argument: '-wd4345'
clang.exe: error: unknown argument: '-wd4351'
clang.exe: error: unknown argument: '-wd4355'
clang.exe: error: unknown argument: '-wd4456'
clang.exe: error: unknown argument: '-wd4457'
clang.exe: error: unknown argument: '-wd4458'
clang.exe: error: unknown argument: '-wd4459'
clang.exe: error: unknown argument: '-wd4503'
clang.exe: error: unknown argument: '-wd4624'
clang.exe: error: unknown argument: '-wd4722'
clang.exe: error: unknown argument: '-wd4800'
clang.exe: error: unknown argument: '-w14062'
clang.exe: error: unknown argument: '-we4238'
clang.exe: error: no such file or directory: 'C:/Program Files (x86)/Git/DWIN32'
clang.exe: error: no such file or directory: 'C:/Program Files (x86)/Git/D_WINDO
WS'
clang.exe: error: no such file or directory: 'C:/Program Files (x86)/Git/W3'
clang.exe: error: no such file or directory: 'C:/Program Files (x86)/Git/MP'
Makefile:22: recipe for target 'all' failed
make: *** [all] Error 1
It says there are no arguments like -wd4146 etc, but I haven't passed those to the clang compiler, and a quick google search shows know helpful answers on what these mean. This is what my build file looks like:
LCC = clang
LCXX = clang++
LLVM_CC_FLAGS=`llvm-config --cflags`
LLVM_LINK_FLAGS=`llvm-config --libs --cflags --ldflags core analysis executionengine jit interpreter native`
C_FLAGS = -Wall -Iincludes/
CXX_FLAGS = -Wall -Wextra -Wno-self-assign
SOURCES = src/*.c
all: ${SOURCES}
${LCC} ${LLVM_CC_FLAGS} ${C_FLAGS} ${SOURCES} -c ${SOURCES}
${LCXX} ${LLVM_LINK_FLAGS} *.o ${LLVM_FLAGS} -o j4
-rm *.o
The output from llvm-config --cflags
-IC:/LLVM/llvm/include -IC:/LLVM/llvm-new-build/include /DWIN32 /D_WINDOWS /W3
/MP -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEP
RECATE -D_CRT_NONSTDC_NO_WARNINGS -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WA
RNINGS -wd4146 -wd4180 -wd4244 -wd4258 -wd4267 -wd4291 -wd4345 -wd4351 -wd4355 -
wd4456 -wd4457 -wd4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4800 -w14062 -we4238 -
D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

Answer 1

This question really has several layers, so I'm going to try to break this down into three parts: a discussion of what is happening inside the backticks, the unknown argument errors, and the no such file or directory errors.
What is llvm-config?
llvm-config is a tool for the LLVM infrastructure that gets configuration information needed to compile programs that need LLVM. So in response to the comment at 1, llvm-config actually is intended for use with clang when clang is used to compile an LLVM project.
The --cflags option gives C compiler flags including LLVM headers, which you saw in the output to llvm-config --cflags. You said
"It says there are no arguments like -wd4146 etc, but I haven't passed those to the clang compiler"
But by putting it in backticks, your shell took the output from llvm-config --cflags and pasted it into your original command. So you did include those arguments, you just didn't realize it!
I will also note that the output from llvm-config is highly dependent on your build system and the version of LLVM. For example, when installed on Ubuntu Linux 14.05, LLVM 3.5 with GNU Make and Ninja generators, the output from llvm-config --cflags is:
-I/.../llvm-3.5.0/llvm/include -I/.../llvm-3.5.0/build/include -fPIC -Wall -W -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -pedantic -Wno-long-long -Wno-comment -ffunction-sections -fdata-sections -g -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
It noticeably doesn't include any of your offending options like -wd4146 or -wd4180 nor any reference to Windows or preprocessor arguments.
What are those weird options like /DWIN32, /D_WINDOWS, /W3, and /MP?
/D defines a preprocessing symbol for a source file, in this case WIN32 and _WINDOWS. 2
/W3 directs MSVC to display level 1, level 2 and level 3 (production quality) warnings. 3
/MP causes MSVC to create multiple instances of itself and attempt to build the project in parallel. 4
The problem is that they're passed to the compiler's arguments prefixed with a forward slash (notice that all other options were passed with a hyphen). As a result, your build is attempting to handle those as file names, as indicated by the resulting errors, for example:
clang.exe: error: no such file or directory: 'C:/Program Files (x86)/Git/DWIN32'
Why it's looking in C:/Program Files (x86)/... is up to some aspect of your LLVM installation and/or your operating system. I'm going to guess it's the last location in your execution path or it is your present working directory.
What are those weird options like -wd4146 and -wd4180?
Those are options to disable certain warnings emitted for MSVC. For example, C4146 is "unary minus operator applied to unsigned type, result still unsigned" and C4180 is "qualifier applied to function type has no meaning; ignored"
Here's an example of doing the exact same thing, but from inside a GNU Make file instead of from the command line (look at the block beginning if (MSVC))
So why isn't my project building?
I can't answer this authoritatively without inspecting your LLVM build. However,
Unknown argument: You've discovered an incompatibility between your version of llvm-config and clang. You noted that you added C:\LLVM\llvm-new-build\Debug\bin to your path, but that doesn't assure that the binary actually executed for each of llvm-config and clang came from the same location. If you had previously installed a canonical, pre-built binary of clang for generic compilation usage, its location will be earlier in your path than C:\LLVM\llvm-new-build\Debug\bin. It's unlikely that llvm-config was included in your pre-built binaries. The reason this matters is that if there's a mismatch between versions, the required include flags generated by llvm-config might not match the required include flags needed by clang. You can verify that execution path shadowing is not happening using which on Unix-like machines and where.exe on Windows machines after Windows Server 2003. We expect that they will both reflect that the execution path is in fact C:\LLVM\llvm-new-build\Debug\bin. If not, there's your problem. I believe that this is what created the issues with options like -wd4146 and -wd4180, etc.
No such file or directory: When you built LLVM, cmake detected you were building on Windows, and produced Visual Studio generator files. Meanwhile, your project appears to use some sort of GNU Make-like build system. See here for more discussion of selecting generators at installation. I believe that the mix between MSVC and another GNU Make-like build system is what created the issues with options like /DWIN32, /D_WINDOWS, /W3, and /MP.