[CMake] Assembly language support using gcc or gas

[Glenn Coombs]

Previously with cmake 2.8.4 we were using these lines to compile an assembly
language file in our project:

if(UNIX)
    enable_language(ASM)

# see if we are building 32-bit or 64-bit executables
    file(WRITE ${CMAKE_BINARY_DIR}/check_32or64bit.cpp "int main(int argc,
char *argv[]) { return 8 * sizeof(char *); }\n")

    try_run(
        run_result
        compile_result
        ${CMAKE_BINARY_DIR}
${CMAKE_BINARY_DIR}/check_32or64bit.cpp
        )

    if (${run_result} EQUAL 32)
        list(APPEND sources "src/sysc/qt/md/i386.s")
        if(APPLE)
            set(ASM_SYS_FLAGS "-arch i386")
        else()
            set(ASM_SYS_FLAGS "-32")
        endif()
    else()
        list(APPEND sources "src/sysc/qt/md/iX86_64.s")
        if(APPLE)
            set(ASM_SYS_FLAGS "-arch x86_64")
        else()
            set(ASM_SYS_FLAGS "-64")
        endif()
    endif()

    set(CMAKE_ASM${ASM_DIALECT}_COMPILE_OBJECT
"<CMAKE_ASM${ASM_DIALECT}_COMPILER> ${ASM_SYS_FLAGS} -o <OBJECT> <SOURCE>")
endif()

And this resulted in the appropriate 32-bit or 64-bit assembler file being
compiled like so:

    /usr/bin/as  -32 -o <path snipped>/i386.s.o      <path-snipped>/i386.s
    /usr/bin/as  -64 -o <path snipped>/iX86_64.s.o <path-snipped>/iX86_64.s

Now with cmake 2.8.5 it fails when compiling that assembler file as it uses
/usr/bin/gcc rather than /usr/bin/as and gcc wants -m32 and -c instead of
-32.  When I tried commenting out the line that overrides the default
setting of CMAKE_ASM${ASM_DIALECT}_COMPILE_OBJECT it fails differently:

/usr/bin/gcc  -DEXTERNAL_BUS_WIDTH=128 -DLINUX -DHIDEBUG -O3 -DNDEBUG
-I/user/grc/msvdx-cvsfiles/sim/msvdx-cmake-2.8.5/systemC/src
-I/user/grc/msvdx-cvsfiles/sim/msvdx-cmake-2.8.5/systemC/src/sysc/kernel
-DNOMINMAX -DUSE_SIM_NAMESPACE -o
CMakeFiles/systemc.dir/src/sysc/qt/md/i386.s.o -c
/user/grc/msvdx-cvsfiles/sim/msvdx-cmake-2.8.5/systemC/src/sysc/qt/md/i386.s

i386.s:69: Error: suffix or operands invalid for `push'

This line works if I add the -m32 option using set(CMAKE_ASM_FLAGS "-m32")
but should all the preprocessor defines (-DXXX) and include directory
arguments (-IXXX) be present ?  I was thinking they were only for C/C++
files, no ?

And what is the recommended way to compile an assembly language file that
will work on both 2.8.4 and 2.8.5 ?

--
Glenn
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