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Compilation failure with clang 6 or 7 #350

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joelagnel opened this issue Jan 15, 2019 · 4 comments
Closed

Compilation failure with clang 6 or 7 #350

joelagnel opened this issue Jan 15, 2019 · 4 comments
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bug Something isn't working build Issues or PRs related to bpftrace building

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@joelagnel
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Hi, I am attempting to build inside a debian chroot on Android.

I get the following build errors when compiling bpftrace with clang:

error: invalid argument '-std=c++14' not allowed with 'C'
make[2]: *** [resources/CMakeFiles/resources.dir/build.make:63: resources/CMakeFiles/resources.dir/headers.c.o] Error 1

My cmake command looks like

mkdir build; cd build; cmake -DCMAKE_BUILD_TYPE=DEBUG -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_C_COMPILER=clang-7 -DCMAKE_CXX_COMPILER=clang++-7 ..

BCC itself builds and works fine with the same clang. Its bpftrace failing to build.

This seems similar to: #159 . Any thoughts @brendangregg ?
@mmarchini mmarchini added bug Something isn't working build Issues or PRs related to bpftrace building labels Jan 15, 2019
@mmarchini
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Not related to #159 because here compiler is complaining that we are using -std=c++14 when building a .c file (more specifically, the resources/headers.c file generated by resources/CMakeList.txt). GCC only warn about this and ignores the parameter.

I'll send a PR to fix this shortly.

mmarchini added a commit to mmarchini/bpftrace that referenced this issue Jan 15, 2019
@mmarchini
resources: generate c++ file instead of c file
faf33ea 
If we use clang to build bpftrace instead of GCC, it will complain about
trying to use the `-std-c++14` flag to comile headers.c. If we force
cmake to skip this flag on `.c` files, clang is not able to link
libresources.a correctly.

This patch changes the resources workflow to generate a .cpp file
instead, and to have a `src/headers.h` with all headers we currently
use. With this approach we get a safer linkage because the same
definition for the header strings is being used in clang_parser.cpp and
in headers.cpp.

Fixes: bpftrace#350
This was referenced Jan 15, 2019
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mmarchini added a commit to mmarchini/bpftrace that referenced this issue Jan 16, 2019
@mmarchini
resources: generate c++ file instead of c file
9ede6c6 
If we use clang to build bpftrace instead of GCC, it will complain about
trying to use the `-std-c++14` flag to comile headers.c. If we force
cmake to skip this flag on `.c` files, clang is not able to link
libresources.a correctly.

This patch changes the resources workflow to generate a .cpp file
instead, and to have a `src/headers.h` with all headers we currently
use. With this approach we get a safer linkage because the same
definition for the header strings is being used in clang_parser.cpp and
in headers.cpp.

Fixes: bpftrace#350
@joelagnel
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Thanks a lot @mmarchini , I verified that this fixes the build.

mmarchini added a commit that referenced this issue Jan 16, 2019
@mmarchini
resources: generate c++ file instead of c file
5e1350b 
If we use clang to build bpftrace instead of GCC, it will complain about
trying to use the `-std-c++14` flag to comile headers.c. If we force
cmake to skip this flag on `.c` files, clang is not able to link
libresources.a correctly.

This patch changes the resources workflow to generate a .cpp file
instead, and to have a `src/headers.h` with all headers we currently
use. With this approach we get a safer linkage because the same
definition for the header strings is being used in clang_parser.cpp and
in headers.cpp.

Fixes: #350
@asutherland
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I think this may have been regressed by 69cbd85 which introduced a simple_struct.c. I just tried to build from a fresh checkout and got the following error while running make:

error: invalid argument '-std=c++14' not allowed with 'C'
tests/CMakeFiles/simple_struct.dir/build.make:62: recipe for target 'tests/CMakeFiles/simple_struct.dir/testprogs/simple_struct.c.o' failed
tests/CMakeFiles/simple_struct.dir/build.make:61: *** [tests/CMakeFiles/simple_struct.dir/testprogs/simple_struct.c.o] Error 1

(I am building using clang-7 at the implied direction of https://github.com/iovisor/bpftrace/blob/master/INSTALL.md#building-bpftrace-1).

I was able to workaround the problem by altering the root CMakeLists.txt like so:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d9e5f5c..f416bda 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -96,9 +96,6 @@ include_directories(SYSTEM ${CLANG_INCLUDE_DIRS})
 add_subdirectory(src/arch)
 add_subdirectory(src/ast)
 add_subdirectory(src)
-if (BUILD_TESTING)
-  add_subdirectory(tests)
-endif()
 add_subdirectory(resources)
 add_subdirectory(tools)
 add_subdirectory(man)

@mmarchini
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Interesting, thanks for reporting this @asutherland, I'll take a look.

You can also work around this issue by passing -DBUILD_TESTING=OFF to cmake (instead of changing CMakeLists.txt).

@mmarchini mmarchini mentioned this issue Sep 12, 2019
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@joelagnel @asutherland @mmarchini