Windows re_syntax_options

[jmkristian]

When building regex for Windows, don't repeatedly define the global variable re_syntax_options.

[jmkristian]

When I tried building without this change, the output from make -j4 contained numerous lines like:

/usr/lib/gcc/x86_64-w64-mingw32/10/../../../../x86_64-w64-mingw32/bin/ld: CMakeFiles/direwolf.dir/ax25_link.c.o:ax25_link.c:(.bss+0x0): multiple definition of `re_syntax_options'; CMakeFiles/direwolf.dir/direwolf.c.o:direwolf.c:(.bss+0x0): first defined here
/usr/lib/gcc/x86_64-w64-mingw32/10/../../../../x86_64-w64-mingw32/bin/ld: CMakeFiles/direwolf.dir/ax25_pad.c.o:ax25_pad.c:(.bss+0x4): multiple definition of `re_syntax_options'; CMakeFiles/direwolf.dir/direwolf.c.o:direwolf.c:(.bss+0x0): first defined here
/usr/lib/gcc/x86_64-w64-mingw32/10/../../../../x86_64-w64-mingw32/bin/ld: CMakeFiles/atest.dir/decode_aprs.c.o:decode_aprs.c:(.bss+0x0): multiple definition of `re_syntax_options'; CMakeFiles/atest.dir/ax25_pad.c.o:ax25_pad.c:(.bss+0x4): first defined here

I used Windows 8.1 Pro. I didn't install the Cygwin packages libboost_regex or perl-Regexp-Common. The output from cmake -DUNITTEST=1 .. contained:

-- The C compiler identification is GNU 10.2.0
-- The CXX compiler identification is GNU 10.2.0
-- Dire Wolf Version: 1.7.0-7fa91dd
-- Build type set to: Release
CMake system: CYGWIN
-- Target architecture: x86_64
-- Could NOT find HAMLIB (missing: HAMLIB_LIBRARY HAMLIB_INCLUDE_DIR)

[stltracker]

An alternative fix to this problem is to add -fcommon to CMAKE_C_FLAGS:

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -203,9 +203,9 @@ if (C_CLANG OR C_GCC)
#
###set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wvla -ffast-math -ftree-vectorize -D_XOPEN_SOURCE=600 -D_DEFAULT_SOURCE ${EXTRA_FLAGS}")
if(FREEBSD)
- set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wvla -ffast-math -ftree-vectorize -D_DEFAULT_SOURCE ${EXTRA_FLAGS}")
+ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wvla -ffast-math -ftree-vectorize -fcommon -D_DEFAULT_SOURCE ${EXTRA_FLAGS}")
else()
- set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wvla -ffast-math -ftree-vectorize -D_GNU_SOURCE ${EXTRA_FLAGS}")
+ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wvla -ffast-math -ftree-vectorize -fcommon -D_GNU_SOURCE ${EXTRA_FLAGS}")
endif()
#
#

[wb2osz]

This is due to a change in gcc behavior:

https://gcc.gnu.org/gcc-10/changes.html

GCC now defaults to -fno-common. As a result, global variable accesses are more efficient on various targets. In C, global variables with multiple tentative definitions now result in linker errors. With -fcommon such definitions are silently merged during linking.

[wb2osz]

This has been added to the 'dev' development branch.
Thanks for identifying and fixing the problem.