DECLSPEC_IMPORT make all curl_cv_func_recv_test Failed when building in windows

[Ron2014]

When I built curl in my project, I found all the recv_test/send_test failed.
But I can build successfully in curl-curl-7-67-0.git.
So I message something in OtherTests.cmake and CheckCSourceCompiles.cmake to check what's the different between these two project. And I found this:

-- Performing Test curl_cv_func_recv_test
====== CMAKE_BINARY_DIR = E:/TestCode/curl-curl-7_67_0/build
====== CMAKE_FILES_DIRECTORY = /CMakeFiles
====== CMAKE_REQUIRED_DEFINITIONS =  -D_WINSOCKAPI_= -DSECURITY_WIN32
====== CHECK_C_SOURCE_COMPILES_ADD_LINK_OPTIONS =
====== CHECK_C_SOURCE_COMPILES_ADD_LIBRARIES = LINK_LIBRARIES;ws2_32
====== MACRO_CHECK_FUNCTION_DEFINITIONS = -Dcurl_cv_func_recv_test
====== CHECK_C_SOURCE_COMPILES_ADD_INCLUDES = -DINCLUDE_DIRECTORIES:STRING=E:/TestCode/curl-curl-7_67_0/include
====== COMPILE_DEFINITIONS =
====== CMAKE_FLAGS =
====== _FAIL_REGEX =
====== OUTPUT = Change Dir: E:/TestCode/curl-curl-7_67_0/build/CMakeFiles/CMakeTmp

Run Build Command(s):D:/Program Files (x86)/Microsoft Visual Studio/2017/Community/MSBuild/15.0/Bin/MSBuild.exe cmTC_8df82.vcxproj /p:Configuration=Debug /p:Platform=Win32 /p:VisualStudioVersion=15.0 /v:m && Microsoft (R) Build Engine version 15.9.21+g9802d43bc3 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  Microsoft (R) C/C++ Optimizing Compiler Version 19.16.27034 for x86
  Copyright (C) Microsoft Corporation.  All rights reserved.

  cl /c /I"E:\TestCode\curl-curl-7_67_0\include" /Zi /W3 /WX- /diagnostics:classic /Od /Ob0 /Oy- /D WIN32 /D _WINDOWS /D curl_cv_func_recv_test /D _WINSOCKAPI_= /D SECURITY_WIN32 /D "CMAKE_INTDIR=\"Debug\"" /D _MBCS /Gm- /RTC1 /MDd /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /Fo"cmTC_8df82.dir\Debug\\" /Fd"cmTC_8df82.dir\Debug\cmTC_8df82.pdb" /Gd /TC /analyze- /errorReport:queue "E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\src.c"
  src.c

E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\src.c(10): warning C4273: 'recv': inconsistent dll linkage [E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\cmTC_8df82.vcxproj]
  D:\Windows Kits\10\Include\10.0.17763.0\um\winsock2.h(2002): note: see previous definition of 'recv'
  cmTC_8df82.vcxproj -> E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\Debug\cmTC_8df82.lib


-- Performing Test curl_cv_func_recv_test - Success
-- Tested: int recv(SOCKET, char *, int, int)

in curl-curl-7-67-0.git, recv can be tested successfully but with an warning, and in my project, treat warning as error, so all recv test failed.

To fix this waning, I check the WinSock2.h and found that function recv/send have WINSOCK_API_LINKAGE description like this:

#if INCL_WINSOCK_API_PROTOTYPES
WINSOCK_API_LINKAGE
int
WSAAPI
recv(
    _In_ SOCKET s,
    _Out_writes_bytes_to_(len, return) __out_data_source(NETWORK) char FAR * buf,
    _In_ int len,
    _In_ int flags
    );
#endif /* INCL_WINSOCK_API_PROTOTYPES */

and then I found WINSOCK_API_LINKAGE == DECLSPEC_IMPORT == __declspec (dllimport)

BUT, we don't need anything in front of the function recv/send, RIGHT?

so I change OtherTests.cmake to:

macro(add_header_include check header)
  if(${check})
    set(_source_epilogue "${_source_epilogue}\n#define DECLSPEC_IMPORT\n#include <${header}>")
  endif()
endmacro()

build again and no warning. SO I recommend this change.

Did anybody deal with the same problem?

[jay]

I don't have that problem. This computer has an old version of Visual Studio but I used a recent cmake, cmake-3.15.5-win64-x64.msi. Try from scratch.

mkdir X:\j\curl\cmake\cmake
cd /d X:\j\curl\cmake\cmake
set PATH=X:\j\curl\cmake\cmake\src\Debug;X:\j\curl\cmake\cmake\lib\Debug;X:\j\curl\cmake\openssl\bin;%PATH%
cmake ..\..\curl -G "Visual Studio 10" -DCMAKE_USE_OPENSSL=ON -DOPENSSL_ROOT_DIR=X:\j\curl\cmake\openssl -DBUILD_TESTING=OFF -DCURL_ZLIB=OFF -DENABLE_THREADED_RESOLVER=ON -DCMAKE_INSTALL_PREFIX:PATH=X:\j\curl\cmake\curl-install-dir

-- Performing Test curl_cv_recv
-- Performing Test curl_cv_recv - Success
-- Performing Test curl_cv_func_recv_test
-- Performing Test curl_cv_func_recv_test - Success
-- Tested: int recv(SOCKET, char *, int, int)
-- Performing Test curl_cv_send
-- Performing Test curl_cv_send - Success
-- Performing Test curl_cv_func_send_test
-- Performing Test curl_cv_func_send_test - Success
-- Tested: int send(SOCKET, const char *, int, int)

[Ron2014]

I don't have that problem. This computer has an old version of Visual Studio but I used a recent cmake, cmake-3.15.5-win64-x64.msi. Try from scratch.

mkdir X:\j\curl\cmake\cmake
cd /d X:\j\curl\cmake\cmake
set PATH=X:\j\curl\cmake\cmake\src\Debug;X:\j\curl\cmake\cmake\lib\Debug;X:\j\curl\cmake\openssl\bin;%PATH%
cmake ..\..\curl -G "Visual Studio 10" -DCMAKE_USE_OPENSSL=ON -DOPENSSL_ROOT_DIR=X:\j\curl\cmake\openssl -DBUILD_TESTING=OFF -DCURL_ZLIB=OFF -DENABLE_THREADED_RESOLVER=ON -DCMAKE_INSTALL_PREFIX:PATH=X:\j\curl\cmake\curl-install-dir

-- Performing Test curl_cv_recv
-- Performing Test curl_cv_recv - Success
-- Performing Test curl_cv_func_recv_test
-- Performing Test curl_cv_func_recv_test - Success
-- Tested: int recv(SOCKET, char *, int, int)
-- Performing Test curl_cv_send
-- Performing Test curl_cv_send - Success
-- Performing Test curl_cv_func_send_test
-- Performing Test curl_cv_func_send_test - Success
-- Tested: int send(SOCKET, const char *, int, int)

Let me explain it.

I treat warning as error in my project. That the key. Which means I use /WX in MSVC like this:

set(CMAKE_C_FLAGS "/MP /WX /TC /errorReport:queue /DWIN32")

What made me test recv failed is the warning C4273. Generally, the warning isn't printed.

Why I can get this warning printed, like this-----

====== OUTPUT = Change Dir: E:/TestCode/curl-curl-7_67_0/build/CMakeFiles/CMakeTmp

Run Build Command(s):D:/Program Files (x86)/Microsoft Visual Studio/2017/Community/MSBuild/15.0/Bin/MSBuild.exe cmTC_8df82.vcxproj /p:Configuration=Debug /p:Platform=Win32 /p:VisualStudioVersion=15.0 /v:m && Microsoft (R) Build Engine version 15.9.21+g9802d43bc3 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  Microsoft (R) C/C++ Optimizing Compiler Version 19.16.27034 for x86
  Copyright (C) Microsoft Corporation.  All rights reserved.

  cl /c /I"E:\TestCode\curl-curl-7_67_0\include" /Zi /W3 /WX- /diagnostics:classic /Od /Ob0 /Oy- /D WIN32 /D _WINDOWS /D curl_cv_func_recv_test /D _WINSOCKAPI_= /D SECURITY_WIN32 /D "CMAKE_INTDIR=\"Debug\"" /D _MBCS /Gm- /RTC1 /MDd /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /Fo"cmTC_8df82.dir\Debug\\" /Fd"cmTC_8df82.dir\Debug\cmTC_8df82.pdb" /Gd /TC /analyze- /errorReport:queue "E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\src.c"
  src.c

E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\src.c(10): warning C4273: 'recv': inconsistent dll linkage [E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\cmTC_8df82.vcxproj]
  D:\Windows Kits\10\Include\10.0.17763.0\um\winsock2.h(2002): note: see previous definition of 'recv'
  cmTC_8df82.vcxproj -> E:\TestCode\curl-curl-7_67_0\build\CMakeFiles\CMakeTmp\Debug\cmTC_8df82.lib

Because I used Everything to find the file CheckCSourceCompiles.cmake in my cmake installation path which defined macro check_c_source_compiles you used in OtherTests.cmake. like include(CheckCSourceCompiles).

I added a message here and see the content of ${OUTPUT} have a warning C4273.

In Brief,

1. Add /WX complie flag for your MSVC project and you will test fail.
2. message the OUTPUT in file CheckCSourceCompiles.cmake in the CMake installation path and you will see the warning which made you test fail.

Pls try it.

PS.
Why you test successfully??
I don't see the /WX flag, maybe when we use cmake . command, it use /WX- as default, which means don't treat warnings as errors.

[jay]

I've retested with -DCURL_WERROR=ON (which adds /WX) and there was no change. I am not too familiar with cmake and so I don't know if what you are doing is correct. Hopefully someone else that follows this project and knows about cmake can help.

[Ron2014]

I've retested with -DCURL_WERROR=ON (which adds /WX) and there was no change. I am not too familiar with cmake and so I don't know if what you are doing is correct. Hopefully someone else that follows this project and knows about cmake can help.

Pay attention to the lineno of code in CMakeLists.txt

/WX is set after include(OtherTests.cmake), so the flag doesn't work for the recv/send test.

1130: include(CMake/OtherTests.cmake)
...
1154: if(CURL_WERROR)
1155:      if(MSVC_VERSION)
1156:          set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
...

So test with -DCURL_WERROR=ON is not a proper way, write set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX") at the first line of CMakeLists.txt and you will get the fails I got.

This is what happend in my work. I use cURL source code as subproject for my MSVC solution. In the main project, I set /WX in the CMakeLists.txt of root directory, which will be passed through add_subdirectory(curl) and finally it works for the recv/send test.

For the familiar with cmake, recommend official tutorial. What I told above and used in my project CMakeLists.txt files all come from the first five steps.

[jay]

Ok I can reproduce that here. I have no idea if that's allowed or expected. Someone that works with libcurl's cmake build system will have to review this.

[bradking]

@Ron2014 please see an alternative fix in #5232. We should match the linkage to make sure the test binary can actually link to the symbol.