6.5The Target Environment

The command line options for the assembler, linker, and compiler follow. The assembler is instructed to allow the additional MC68020 opcodes and addressing modes. The compiler is also told to use maximum optimization and not to use a frame pointer if none is required. The linker is instructed not to use standard libraries (remember that we did not build standard libraries for our environments), to use the target addresses specified above for the .TEXT and .DATA sections, and to create a map file. The map file should be checked after the build is completed.

21# compiler and linker flags.

22#

Our source files are the assembler start-up file crt0.S and all files *.cc, assuming that no other files with extension .cc are stored in the directory where the ROM image is made.

30# Source files

31#

32SRC_S := $(wildcard *.S)

33SRC_CC := $(wildcard *.cc)

For each .cc file, the compiler creates a .d file later on, using the -MM option. Rather than making a .cc file dependent of all header (.hh) files, which would lead to re-compiling all .cc files when any header file is changed, this ??? -MM option ??? only causes those .cc files to be compiled that include changed .hh files, which speeds up compilation.

36# Dependency files

37#

38DEP_CC := $(SRC_CC:.cc=.d)

39DEP_S := $(SRC_S:.S=.d)

The object files to be created by the assembler or the compiler:

42# Object files

43#

44OBJ_S := $(SRC_S:.S=.o)

45OBJ_CC := $(SRC_CC:.cc=.o)

The files that are created by the build process and that may thus be deleted without harm:

All object files are placed in a library called libos.a. Consequently, only the code that is actually required is included in the ROM image. If code size becomes an issue, then one can break down the source files into smaller source files, containing for instance only one function each. Linking is usually performed at file level, so that for files containing both used and unused functions, the unused functions are included in the final result as well. Splitting larger source files into smaller ones can thus reduce the final code size.

86libos.a:$(OBJ)

87$(AR) -sr libos.a $?

The final ROM image, Target, is made by converting the corresponding binary file, Target.bin, into Srecord format. Most EPROM programmers accept both binary and Srecord files. However, Srecord files are more convenient to read or to send by mail, and they also contain checksums.

The file Target.text contains the .TEXT section of the linker’s output Target.td in binary format. It is created by instructing the objcopy to remove the .DATA segment and to store the result in binary format.

92Target.text:Target.td

93$(OBJCOPY) -R .data -O binary $< $@

The file Target.data contains the .DATA section of the linker’s output Target.td in binary format. It is created by instructing the objcopy to remove the .TEXT segment and to store the result in binary format.

95Target.data:Target.td

96$(OBJCOPY) -R .text -O binary $< $@

For the target configuration we have chosen (aout format), a 32 byte header created is created if the .TEXT segment is linked to address 0. This header must be removed, e.g. by a small utility skip_aout which is described below. The file Target.bin is created by removing this header from Target.text and appending

Target.data:

98Target.bin:Target.text Target.data

99cat Target.text | skip_aout | cat - Target.data > $@

The map file Target.sym is created by the nm utility with the linker’s output. The nm is instructed to create a format easier to read by humans then the default output by the option --demangle. From this output, several useless symbols are