UEE072HM Embedded Control Systems

Breaking down the compilation process Compilation is made up of a number of phases –Preprocessing –Compilation Can be a number of passes –Optimisation –Link/loading

The compilation process cc –flags myfile.c thisfile.o PreprocessingCompilationOptimisation*Link/loading #includes.h header files #defines Text Assembler or Object format Relocatable Object file Executable Binary Object files Library file Start-up code *optional

Preprocessing ccp is the C preprocessor –Really a text editor – text input and output –Uses in #include file ( /usr/include in UNIX) –Related to libraries & systems calls through prototypes and struct definitions –Deals with macros and constants –Can get output Cc –E file.c

Compilation This is often called c1 or cl –Can be 1 or 2 passes –Creates either intermediate object format or assembler file –Can contain the optimisation phase turned on/off by a command line flag –Several/separate files can be compiled to object files cc –c file.c creates file.o

Optimisation Can be a separate phase or part of main C compiler Is optional – quite often turned off for cross development

Assembly If the compiler produces assembler code then this can be sent to the assembler It is worth noting –That the assembly code can be non-standard –Debugging may have to be done at assembly level –Can hand optimise –Helpful for understanding ALP/HLL linkage

Link Loading Normally the program ld, gld, l1 Can link together various object and library file Controlled by a linker language Produces map and symbol table output Very important for cross development

Program Segments Code Data BSS Stack Heap char strng=“hello”; int count, this, that; main() { int i, j, k; char *sp; …….. for (i=0;i != 100;i++) …… sp= (char*) malloc(sizeof(i));

Executable formats There are a number of different exectuable formats –A.out is the traditional UNIX format –Elf – executable and linking format –COFF – common object format –Plus lots of others

Variable initialisation Some is done by the compiler –.data instructions Some by the linker And some by the operating system

Elf format p_type p_offset p_vaddr p_filesz p_memsz p_flags p_type p_offset p_vaddr p_filesz p_memsz p_flags CODE DATA ‘E’ ‘L’ ‘F’ 0x e_indent e_entry e_phoff e_phentsize e_phnum PT_LOAD 0 0x PF_R, PF_X PT_LOAD x8059BB PF_R, PF_W Physical Header Physical Header