[CMake] add_custom_command using CMAKE_CXX_FLAGS

[John Smith]

Alexander Neundorf wrote:
> On Monday 24 August 2009, John Smith wrote:
>> [...] I have tried doing that. [...] 
> 
> So you have also hit that bug ?
> http://public.kitware.com/Bug/view.php?id=8392
> 

Interesting, did not know of it.

IMHO, I believe that the C compiler (or C compiler driver) should be 
invoked on the assembly sources, with the exact definitions and C 
compiler flags that are set at that point in the processing of the 
source tree. The reason for that is definitions may be involved in 
pre-processing the source file as conditionals guarding include 
directives, etc. and flags may alter the code generation, e.g., -m32 may 
be used to generate x86 code.

If CMake has the concept of a settable "default" language/compiler per 
project then perhaps that default compiler -- be it C or C++ -- might be 
the perfect choice for building the project's assembly files. The C 
compiler would use the compile definitions and C flags, whereas the C++ 
compiler would use the same definitions but CXX flags. I.e., not 
hard-coding the C compiler in might be a better choice. Of course, I 
might be wrong, and I invite others to state their opinions on this.

gcc -- per the man page -- does not preprocess .s files but it does so 
for .S files, when invoked for compilation. With this behavior, I 
believe gcc is unique.

Other compilers which I believe know automagically what to do with .s 
assembly sources are:

1. HP aCC at http://tinyurl.com/nhr97k :

Assembly language source files (.s files)
Files with names ending in .s are assumed to be assembly source files. 
The compiler invokes the assembler through cc to produce .o files from 
these.

2. IBM VisualAge for C++ at http://tinyurl.com/l2lqt4 :

Assembler files
Assembler files must have a .s suffix, for example, file_name.s, unless 
you compile with the -qsourcetype=assembler option. Assembler files are 
assembled to create an object file.

3. Sun's Sun Studio at http://tinyurl.com/ma6etm :

The syntax of the cc command is:
% cc [options] filenames [libraries]...
[...]
Use the C compiler to compile and link any combination of the following:
[...] o Assembler source files, with .s suffixes

4. Intel C++ at http://tinyurl.com/6lxedl :

The Intel® C++ Compiler recognizes input files with the extensions 
listed in the following table:

[...]
file.s   |   Assembly file    |     Passed to assembler

> Can you please try the attached patch ?

Sure thing, I will.

Thanks!