Configure option --with-cxx-main=/usr/bin/clang++ not working #93744

MaxwellDupre · 2022-06-12T11:16:56Z

Configure option --with-cxx-main=/usr/bin/clang++ not working

My environment

CPython versions tested on:
Latest 3.12.0.a0 tried on other but CC=/usr/bin/clang not working on those, so pointless to try
Operating system and architecture:
fedora 5.17.13-300.fc36.x86_64

Configure options
--with-cxx-main=/usr/bin/clang++ CC=/usr/bin/clang
runs and gives at end:
configure: creating Modules/Setup.local
configure: creating Makefile
configure:

Then:
make
/usr/bin/clang++ -c -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden -I./Include/internal -I. -I./Include -DPy_BUILD_CORE -o Programs/python.o ./Programs/python.c
clang-14: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
error: invalid argument '-std=c11' not allowed with 'C++'
make: *** [Makefile:1373: Programs/python.o] Error 1

See Discuss report

Tried configure with --with-cxx-main=/usr/bin/g++ CC=/usr/bin/gcc
then
make
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: command-line option ‘-std=c11’ is valid for C/ObjC but not for C++

Shows source files being compiled and linked and actually builds python executable, so this works.

The text was updated successfully, but these errors were encountered:

kumaraditya303 · 2022-06-19T09:20:06Z

If you do CC=clang ./configure it works fine. This is not a Python bug, you can ask this on discourse Users category.

MaxwellDupre · 2022-06-21T09:20:03Z

This is a bug: explain why its not!

I have raised a question on discourse and it was not answered!

I am not complaining about CC=clang ./configure - this works for me BUT the option
--with-cxx-main=/usr/bin/clang++ CC=/usr/bin/clang
does not!!!

tiran · 2022-06-21T09:46:21Z

I can reproduce the problem and confirm that it's a bug in our configure script.

$ CC=clang ../../configure --with-cxx-main=clang++ -C
$ make -j1
clang++ -c -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I../../Include/internal -IObjects -IInclude -IPython -I. -I../../Include    -DPy_BUILD_CORE -o Programs/python.o ../../Programs/python.c
clang-14: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
error: invalid argument '-std=c11' not allowed with 'C++'
make: *** [Makefile:1376: Programs/python.o] Error 1

erlend-aasland · 2022-06-21T09:49:51Z

This is a bug: explain why its not!

Please remain calm and use a polite tone.

I have raised a question on discourse and it was not answered!

25 minutes ago. There is no guarenteed response time; we are all volunteers, trying to improve CPython in our free time. Once again, please use a polite tone.

kumaraditya303 · 2022-06-21T09:58:43Z

The discuss report ¹ you linked has been answered by a core dev and the author claimed that by syncing with 3.12 it works and then you are saying that it has not been answered. Please remain calm so that our autoconf experts will take a look. Thanks

https://discuss.python.org/t/compiling-python-with-clang/16323/4 ↩

tiran · 2022-06-21T10:26:06Z

GCC's C++ compiler just warns about -stdc=c11 option. Do we support building with Clang's C++ compiler?

g++ -c -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Werror=implicit-function-declaration -fvisibility=hidden  -I../../Include/internal -IObjects -IInclude -IPython -I. -I../../Include    -DPy_BUILD_CORE -o Programs/python.o ../../Programs/python.c
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++
cc1plus: warning: command-line option ‘-std=c11’ is valid for C/ObjC but not for C++

erlend-aasland · 2022-06-21T10:28:10Z

Do we support building with Clang's C++ compiler?

AFAICS, no C++ is mentioned in PEP 11. However, @vstinner has recently pushed some changes to make the code base friendlier to C++ compilers.

encukou · 2022-06-21T11:09:31Z

AFAIK Victor's work is on public headers, not Python itself. While you can use the C-API with C++, Python itself is written in C.

Supporting ./configure with C++ seems rather pointless to me, is there a use case where you can't use the C compiler?

erlend-aasland · 2022-06-21T11:11:10Z

AFAIK Victor's work is on public headers, not Python itself [...]

Yes, correct. That's a related issue, but not directly relevant for this issue.

erlend-aasland · 2022-06-21T11:13:43Z

See also the docs for the --with-cxx-main option: https://docs.python.org/3/using/configure.html

tiran · 2022-06-21T11:15:03Z

--with-cxx-main is a feature that was introduced in 9501219 (1999). Is still useful?

erlend-aasland · 2022-06-21T11:17:18Z

Here's my 2 cents:

PEP 11 does not say anything about C++ compilers. The current option is broken with ~~at least one C++ compiler~~ two C++ compilers.
I say we drop it.

encukou · 2022-06-21T11:45:32Z

I guess the use case might have been ensuring that we can use a C++ compiler/linker with libpython? testcppext does that now.

Anyway, if we do drop it, 3.12a0 is the perfect time.

vstinner · 2022-06-21T12:56:29Z

See also the docs for the --with-cxx-main option: https://docs.python.org/3/using/configure.html

I never used it. I don't see the point of building the whole Python in C... but only the main() function with C++.

Nowadays, most Linux distributions distribute a shared libpython library, so it's trivial to build your own main() function implemented in C++ which calls Py_BytesMain().

Each time I tried --with-cxx-main, I only got errors and I failed to understand its purpose.

I suggest to remove this configure option.

vstinner · 2022-06-21T12:57:51Z

PEP 11 does not say anything about C++ compilers.

It would be nice to update PEP 11 to require the Python C API to be usable in C++, at least with C++11.

Since Python 3.11, compatibility with C++11 is now tested. I recently added a test on C++03.

vstinner · 2022-06-21T13:04:09Z

On Fedora 36, I failed to build Python 3.10 with ./configure --with-cxx-main=g++ CC=gcc. g++ fails to build Programs/_testembed.c.

So I don't think that this issue is about fixing Python. It's like a "new feature". IMO configure --with-cxx-main=... option was broken for many years.

Examples of g++ errors:

Include/internal/pycore_atomic.h is incompatible C++:

./Include/internal/pycore_atomic.h:38:32: error: 'memory_order_relaxed' was not declared in this scope
   38 |     _Py_memory_order_relaxed = memory_order_relaxed,

putenv() error:

./Programs/_testembed.c:168:12: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
  168 |     putenv("PYTHONMALLOC=");

Many errors related to Py_BUILD_ASSERT_EXPR() used by Py_ARRAY_LENGTH():

In file included from ./Include/Python.h:51,
                 from ./Programs/_testembed.c:8:
./Include/pymacro.h:61:30: error: '__builtin_types_compatible_p' was not declared in this scope
   61 |      + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./Include/pymacro.h:40:27: note: in definition of macro 'Py_BUILD_ASSERT_EXPR'
   40 |     (sizeof(char [1 - 2*!(cond)]) - 1)
      |                           ^~~~
./Programs/_testembed.c:319:13: note: in expansion of macro 'Py_ARRAY_LENGTH'
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |             ^~~~~~~~~~~~~~~
./Include/pymacro.h:40:13: error: expected primary-expression before 'char'
   40 |     (sizeof(char [1 - 2*!(cond)]) - 1)
      |             ^~~~
./Include/pymacro.h:61:8: note: in expansion of macro 'Py_BUILD_ASSERT_EXPR'
   61 |      + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
      |        ^~~~~~~~~~~~~~~~~~~~
./Programs/_testembed.c:319:13: note: in expansion of macro 'Py_ARRAY_LENGTH'
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |             ^~~~~~~~~~~~~~~
./Include/pymacro.h:40:13: error: expected ')' before 'char'
   40 |     (sizeof(char [1 - 2*!(cond)]) - 1)
      |            ~^~~~
./Include/pymacro.h:61:8: note: in expansion of macro 'Py_BUILD_ASSERT_EXPR'
   61 |      + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
      |        ^~~~~~~~~~~~~~~~~~~~
./Programs/_testembed.c:319:13: note: in expansion of macro 'Py_ARRAY_LENGTH'
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |             ^~~~~~~~~~~~~~~
./Programs/_testembed.c:319:41: error: expected ')' before ';' token
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |                                         ^
      |                                         )
./Include/pymacro.h:40:5: note: to match this '('
   40 |     (sizeof(char [1 - 2*!(cond)]) - 1)
      |     ^
./Include/pymacro.h:61:8: note: in expansion of macro 'Py_BUILD_ASSERT_EXPR'
   61 |      + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
      |        ^~~~~~~~~~~~~~~~~~~~
./Programs/_testembed.c:319:13: note: in expansion of macro 'Py_ARRAY_LENGTH'
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |             ^~~~~~~~~~~~~~~
./Programs/_testembed.c:319:41: error: expected ')' before ';' token
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |                                         ^
      |                                         )
./Include/pymacro.h:60:5: note: to match this '('
   60 |     (sizeof(array) / sizeof((array)[0]) \
      |     ^
./Programs/_testembed.c:319:13: note: in expansion of macro 'Py_ARRAY_LENGTH'
  319 |     Py_Main(Py_ARRAY_LENGTH(argv), argv);
      |             ^~~~~~~~~~~~~~~

erlend-aasland · 2022-06-21T13:06:48Z

I guess we could remove it under this ticket. Let's go 🚀

Remove "configure --with-cxx-main" option: it didn't work for many years. Remove the following configure and Makefile variables: CXX, LDCXXSHARED, MAINCC. * MAINCC was added by issue pythongh-42471: commit 0f48d98. Previously, --with-cxx-main was named --with-cxx. * LDCXXSHARED was added by issue pythongh-42093: commit 0000295. * CXX variable was used by MAINCC and LDCXXSHARED variables.

vstinner · 2022-06-21T14:33:28Z

I wrote a large PR removing more than just --with-cxx-main: PR #94063.

Remove the "configure --with-cxx-main" build option: it didn't work for many years. Remove the MAINCC variable from configure and Makefile. The MAINCC variable was added by the issue pythongh-42471: commit 0f48d98. Previously, --with-cxx-main was named --with-cxx. Keep CXX and LDCXXSHARED variables, even if they are no longer used by Python build system.

Remove the "configure --with-cxx-main" build option: it didn't work for many years. Remove the MAINCC variable from configure and Makefile. The MAINCC variable was added by the issue gh-42471: commit 0f48d98. Previously, --with-cxx-main was named --with-cxx. Keep CXX and LDCXXSHARED variables, even if they are no longer used by Python build system.

vstinner · 2022-08-05T11:28:04Z

Fixed by 398ed84 which removes the configure option.

It's easy to embed Python in a C++ application: https://docs.python.org/dev/extending/embedding.html

erlend-aasland · 2022-08-05T13:46:51Z

Thanks for the fix, Victor 😃 Closing this as fixed 🚀

MaxwellDupre added the type-bug An unexpected behavior, bug, or error label Jun 12, 2022

kumaraditya303 closed this as not planned Won't fix, can't repro, duplicate, stale Jun 19, 2022

tiran reopened this Jun 21, 2022

erlend-aasland added the build The build process and cross-build label Jun 21, 2022

bedevere-bot mentioned this issue Aug 4, 2022

gh-93744: Remove configure --with-cxx-main option #95651

Merged

erlend-aasland closed this as completed Aug 5, 2022

Configure option --with-cxx-main=/usr/bin/clang++ not working #93744

Configure option --with-cxx-main=/usr/bin/clang++ not working #93744

MaxwellDupre commented Jun 12, 2022

kumaraditya303 commented Jun 19, 2022

MaxwellDupre commented Jun 21, 2022

tiran commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

kumaraditya303 commented Jun 21, 2022 •

edited

tiran commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022 •

edited

encukou commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022 •

edited

tiran commented Jun 21, 2022 •

edited

erlend-aasland commented Jun 21, 2022 •

edited

encukou commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Aug 5, 2022

erlend-aasland commented Aug 5, 2022

Configure option --with-cxx-main=/usr/bin/clang++ not working #93744

Configure option --with-cxx-main=/usr/bin/clang++ not working #93744

Comments

MaxwellDupre commented Jun 12, 2022

kumaraditya303 commented Jun 19, 2022

MaxwellDupre commented Jun 21, 2022

tiran commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

kumaraditya303 commented Jun 21, 2022 • edited

Footnotes

tiran commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022 • edited

encukou commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022 • edited

tiran commented Jun 21, 2022 • edited

erlend-aasland commented Jun 21, 2022 • edited

encukou commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Jun 21, 2022

erlend-aasland commented Jun 21, 2022

vstinner commented Jun 21, 2022

vstinner commented Aug 5, 2022

erlend-aasland commented Aug 5, 2022

kumaraditya303 commented Jun 21, 2022 •

edited

erlend-aasland commented Jun 21, 2022 •

edited

erlend-aasland commented Jun 21, 2022 •

edited

tiran commented Jun 21, 2022 •

edited

erlend-aasland commented Jun 21, 2022 •

edited