Writeln in assembler

scvalex (Alexandru Scvortov) — Mon, 10 Sep 2007 12:14:54 GMT

NASM code for writing the integer in eax to stdout.



segment .bss

        writeTemp       resb    10



segment .text

_writeln:                               

        MOV     ebx,    eax             ; Number is already in eax

        MOV     ecx,    10

        XOR     edi,    edi

L0:

        CMP     eax,    0

        JE      L1

        ADD     edi,    1

        XOR     edx,    edx

        IDIV    ecx

        JMP     L0

L1:

        ADD     edi,    writeTemp       ; Length of the number is in edi

        MOV     esi,    edi

        MOV byte        [edi],  10      ; Add a newline

        SUB     edi,    1

        XOR     eax,    eax

L2:                             

        CMP     ebx,    0

        JE      L3

        MOV     eax,    ebx

        XOR     edx,    edx

        IDIV    ecx

        ADD     dl,     48

        MOV     [edi],  dl

        SUB     edi,    1

        MOV     ebx,    eax

        JMP     L2                      ; Number has been written to writeTemp from tail to head

L3:                             

        MOV     eax,    4

        MOV     ebx,    1

        MOV     ecx,    writeTemp

        MOV     edx,    esi

        SUB     edx,    writeTemp

        ADD     edx,    1

        INT     80h

Automated GNU Makefile

scvalex (Alexandru Scvortov) — Wed, 02 May 2007 17:43:36 GMT

A simple automated GNU Makefile to build and link c/c++/asm projects. All the variables that need to be tweaked are located at the begining:
PROGNAME: the name of the executable to be built
CC: the C compiler
CPP: the C++ compiler
ASM: the assambler
LD: the linker

This searches for all *.c, *.cpp and *.s files and compiles them into objects. It then links all the files into a single executable.

The strip rule is used to strip all unwanted symbols from the resulting executable. This usually results in a significant (think 40%) size optimisation.



$(VERBOSE).SILENT:



PROGNAME = prog



CC = gcc

CC += -c

CPP = g++

CPP += -c

ASM = nasm

ASM += -f elf -d ELF_TYPE

LD = g++



OBJFILES = $(patsubst %.c,%.o,$(wildcard *.c))

OBJFILES += $(patsubst %.s,%.o,$(wildcard *.s))

OBJFILES += $(patsubst %.cpp,%.o,$(wildcard *.cpp))



all: $(PROGNAME)



clean:

	@echo "Cleaning object files"

	@echo "    rm -f     *.o"

	rm -f *.o

	@echo "Cleaning backups"

	@echo "    rm -f     *~"

	rm -f *~

	@echo "Removing programme"

	@echo "    rm -f     "$(PROGNAME)

	rm -f $(PROGNAME)



%.o: %.s

	@echo "Assambling "$@

	@echo "    ASM       "$<

	$(ASM) $<



%.o: %.c

	@echo "Compiling "$@

	@echo "    CC        "$<

	$(CC) $<



%.o: %.cpp

	@echo "Compiling "$@

	@echo "    CPP       "$<

	$(CPP) $<



$(PROGNAME): $(OBJFILES)

	@echo "Linking "$@

	@echo "    LD        -o "$(PROGNAME)"        "$(OBJFILES)

	$(LD) -o $(PROGNAME) $(OBJFILES)



strip: $(PROGNAME)

	@echo "Stripping "$(PROGNAME)

	echo -n "Size of "$(PROGNAME)" before strip is "

	ls -sh $(PROGNAME) | cut -d' ' -f1

	@echo "    strip     "$(PROGNAME)

	strip $(PROGNAME)

	echo -n "Size of "$(PROGNAME)" after strip is "

	ls -sh $(PROGNAME) | cut -d' ' -f1



nothing:

	@echo "Nothing to do; quitting  :("

	@echo "HINT: Try make all"

DZone Snippets: asm code

Writeln in assembler

Automated GNU Makefile