ARMCLANG: Producing dependency file from an assembly file

Information in this knowledgebase article applies to:

• ARMCLANG v6.x compiler toolchain

SYMPTOM

I'm compiling a C file with ARMCLANG compiler with compiler options as follows to produce a dependency file, which works fine

armclang (other flags...) -MP -MMD -MF filename.d -c -o file.o file.c

However, it doesn't produce a dependency file, if I compile an assembly file like this:

armclang (other flags...) -MP -MMD -MF filename.d -c -o file.o file.s

The warning I got from ARMCLANG compiler is:

armclang.exe: warning: argument unused during compilation: '-MP' [-Wunused-command-line-argument]

CAUSE

The ARMCLANG compiler treats the file extension as a hint as to what form of compilation it should perform.

The file extensions *.s and *.S are treated differently by ARMCLANG. A file with *.s (lower case) is an assembly language file and a file with *.S (upper case) is an assembly language file which should be run through the C preprocessor first.

None of the C preprocessor options, such as -Mxx, will be performed on these files, because ARMCLANG does not invoke the C preprocessor for *.s files, by default. This is why the compiler warning above is given.

RESOLUTION

To create the dependency file, choose one of the following options:

• Pass the parameter '-x assembler-with-cpp' to ARMCLANG compiler, which forces the above behavior in spite of the filename. See below:

  armclang (other flags...) -x assembler-with-cpp -MP -MMD -MF filename.d -c -o file.o file.s
  

• Change your file extension to *.S (upper case).

MORE INFORMATION

• Refer to Summary of armclang command-line options

Last Reviewed: Friday, May 22, 2020