[cmake-developers] How to deal with assembler files

[Alexander Neundorf]

Hi,

current support for assembler has the shortcoming that in all cases the 
assembler is called directly (e.g. as, gas, masm, nasm, etc.).
This works as long as the assembler files don't have preprocessor directives 
in them.
But if that's the case, the assembler files should be actually processed by 
the C (or C++ ?) compiler.

Currently you can do
enable_language(ASM)
This should be the somehow generic one.
-> enable the ASM language, which is either "as" or "gas", *.s, *.S, *.asm

enable_language(ASM-ATT)
-> also "as" or "gas", assembler files should be AT&T syntax

enable_language(ASM_MASM)
-> ml.exe or ml64.exe, *.asm, using masm syntax

(ASM_NASM will come soon)

These special versions for assembler are necessary since within one project 
there can be files which need to be processed e.g. with gas, while others 
need to be processed with nasm, so it must be possible to differentiate 
between different assembler files within one project.

Still, there is the preprocessing bug.

So here's my idea how to modify the behaviour:

1)
enable_language(ASM)
will in general use the C compiler for the assembler files. It seems most C 
compilers can do that. This will make these files being preprocessed, and it 
will be the "default" syntax for the toolchain.

When a different asm syntax is needed, this can still be enabled via ASM_ATT, 
ASM_NASM, etc.

2) Only issue: what to do when the C compiler is not able to process assembler 
files ?
It seems e.g. when using the IAR toolchain, the assembler *must* be called for 
asm files, not the C compiler. So here just using the C compiler for ASM 
would fail. But having to enable e.g. "ASM_IAR" should not be necessary, 
since for this toolchain there is probably no other assembler which could be 
used.
How about this: when C and/or C++ are enabled, they can set a hint what to use 
for ASM. E.g. for IAR-C.cmake could "set(CMAKE_ASM_SUGGESTED_COMPILER 
iasmarm)", which could then be preferred by CMakeDetermineASMCompiler.cmake.
It could also directly preset CMAKE_ASM_COMPILER or CMAKE_ASM_COMPILER_INIT.

Does that sound reasonable ?

Alex