I have been following you efforts for a long time now and am very impressed with the level of commitment the members have towards answering people's questions and solving their problems. I would like to join in!
This is my first post here and I am sorry to be posting a question and not an answer. Unfortunately it is my desire to get this issue resolved that has promted me to join and not a Don Quixote form of chivalry.
I am writing an operating system, obviously, and have got to a fairly advanced position. I have managed to boot from a disk boot block and switch in to protected mode and jump to a C kernel. The operating system is currently only single tasking, I am waiting to make the move to a multi tasking system once I have mastered the basics and managed to get all the hardware working well. Currently the operating system has hires VESA graphics linear buffer, NE2000 ethernet support, FPU, serial port, parrallel port and low level PCI drivers. I am moving towards USB and virtual memory support.
The operating system is moving to a point now where every thing is working and development has really sped up due to the nice input/output routines I have developed for getting information out of the machine. Unfortunately I have had the persistant problem with strings for some time now and it is really retarding the rate at which my development is progressing.
I am here to ask you guys/girls if anyone can help me resolve this issue. I have been trying to solve the issue now for months and have burnt many a weekend trying to find the cause of the issue, no luck yet it seems.
THE SYMPTOM:
The code below is trimmed down the the bare essentials:
Code: Select all
static char msg_time[] = "[Time] \n\r"; //1.string declared as global static char array
char msg_console[] = "[CON] init\n\r"; //2.string declared as global char array
void kernel_init()
{
char msg_kernel[] = "[Kernel] init\n\r"; //3.string declared as local char array
static char msg_irq[] = "[IRQ] init\n\r"; //4.string declared as local char array
console_printf(msg_irq); //5.string does not display (pointer is 0 in kernel at rt)
console_printf(msg_time); //6.string does not display (pointer is 0 in kernel at rt)console_printf(msg_console); //7.string displays (pointer is a valid value obviously)
console_printf("hello\n\r"); //8.string does not display (pointer is 0 in kernel at rt)
console_printf(msg_kernel); //9.string displays (pointer is a valid value obviously)
}- 1,4 both appear in a .data section in the assembled code and are in the binary output too.
- 2,3 both appear in code but not inside a .data section and are in the binary output too.
- 7 also appears in the asm and object but does not display.
Code: Select all
.section .data
_msg_time:
.ascii "[Time] \12\15\0"
.globl _msg_shell
_msg_shell:
.ascii "[CON] init\12\15\0"
.section .text
.globl _main
...
LC0:
.ascii "hello\12\15\0"
_msg_kernel:
.ascii "[Kernel] init\0"
.globl _kernel_init
_kernel_init:THE FACTS:
Let me begin by describing my development platform:
Windows XP sp2.
DJGPP GCC 4.1.1.
NASM 0.98.08.
DJGPP GNU Ld 2.19.
GNU Make 3.81.
BOCHS 2.4.1.
Below is the linker script I use to link the kernel objects:
Code: Select all
OUTPUT_FORMAT(coff-go32)
OUTPUT_ARCH(i386)
STARTUP(bld/boot/loader32.o)
INPUT
(
bld/kernel/sys/kernel.o
bld/kernel/sys/system.o
bld/kernel/sys/isr.o
bld/kernel/sys/isr_asm.o
bld/kernel/sys/irq.o
bld/kernel/sys/irq_asm.o
bld/kernel/sys/video.o
bld/kernel/sys/string.o
bld/kernel/sys/time.o
bld/kernel/sys/kb.o
bld/kernel/sys/shell.o
bld/kernel/sys/console.o
bld/kernel/mem/gdt.o
bld/kernel/mem/gdt_asm.o
bld/kernel/mem/idt.o
bld/kernel/mem/idt_asm.o
bld/kernel/mem/vmemory.o
bld/kernel/mem/paging.o
bld/kernel/fpu/fpu.o
bld/kernel/fpu/fpu_asm.o
bld/kernel/pci/pci.o
bld/kernel/pci/pci_asm.o
bld/kernel/net/ne2000.o
bld/kernel/gfx/gfx.o
bld/kernel/gfx/gfx_asm.o
bld/kernel/test/test.o
bld/lib/lang/compiler.o
bld/lib/math/math.o
bld/lib/math/math_asm.o
bld/lib/math/trig.o
bld/lib/math/vector.o
bld/lib/math/matrix.o
)
SECTIONS
{
.text : {
code = .;
*(.text)
*(.rodata)
*(.rdata)
. = ALIGN(4096);
}
.data :
{
data = .;
*(.data)
. = ALIGN(4096);
}
.bss :
{
bss = .;
*(.bss)
*(.comment)
*(COMMON)
. = ALIGN(4096);
}
end = .;
}Code: Select all
OUTPUT_FORMAT(binary)
ENTRY(start)
OUTPUT_ARCH(i386)
STARTUP(bld/boot/loader16.o)
INPUT
(
bld/kernel/kernel.o
)
phys = 0x00000000;
SECTIONS
{
.text phys : AT(phys) {
code = .;
*(.text)
*(.rodata)
*(.rdata)
. = ALIGN(4096);
}
.data : AT(phys + (data - code))
{
data = .;
*(.data)
. = ALIGN(4096);
}
.bss : AT(phys + (bss - code))
{
bss = .;
*(.bss)
*(.comment)
*(COMMON)
. = ALIGN(4096);
}
end = .;
}Code: Select all
#The make used is GNU Make 3.81
#The compiler used to compile this operating system is DJGPP GCC 4.1.1
COMPLIER=G:\sjs\environment\c\compiler\djgpp\4.1.1\bin\gcc.exe
OBJDUMP=G:\sjs\environment\c\tools\objdump.exe
OBJCOPY=G:\sjs\environment\c\tools\objcopy.exe
STRINGS=G:\sjs\environment\c\tools\strings.exe
#These compiler flags report all compiler errors, reduces the strength of the C syntax to C89,
#omits the frame pointer, puts in no built in functions or any of the standard library function librariess.
#omit-frame-pointer = a pointer which can be used to point to sub sections of the stack frame
#note: use the -S to output to assembler
COMPILER_FLAGS=cnf/djgpp.options -> -ffreestanding -minline-all-stringops -fno-merge-debug-strings -fno-inline -O0 -fno-builtin -nostdinc -mcld -Wall -Wextra -Wwrite-strings -Woverlength-strings -fno-strict-aliasing -fno-builtin -fno-stack-protector -fomit-frame-pointer -fstrength-reduce -I./inc
COMPILE_TO_ASSEMBLY=-S
#The assembler used is NASM 0.98.08
ASSEMBLER=G:\sjs\environment\c\tools\nasm.exe
DISASSEMBLER=G:\sjs\environment\c\tools\ndisasmw.exe
#The make used is GNU Make 3.81
LINKER=G:\sjs\environment\c\tools\ld.exe
LINKER_FLAGS=-nostdlib
# LINKER_FLAGS=-nostdlib --warn-common
#The utility which is used to generate the FAT12 image is fat_imgen 2.0.0
FAT12_IMAGE_GENERATOR=G:\sjs\environment\c\tools\fat_imgen.exe
#The emulator used is BOCHS 2.4.1
EMULATOR=G:\sjs\environment\c\emulator\bochs\2.4.1\bochs.exe
#Floppy disk writer RAWRITE
WRITER_DIR=G:\sjs\work\eclipse-cpp-workspace\eclipse-c-project-base\dst
WRITER=G:\sjs\work\eclipse-cpp-workspace\eclipse-c-project-base\dst\rawrite.exe
assemble:
@echo Assembling Kernel Sources
@${ASSEMBLER} -f bin ${SOURCE}$(BOOT)boot.asm -o ${BUILD}$(BOOT)boot.bin
@${ASSEMBLER} -f aout ${SOURCE}$(BOOT)loader16.asm -o ${BUILD}$(BOOT)loader16.o
@${ASSEMBLER} -f coff ${SOURCE}$(BOOT)loader32.asm -o ${BUILD}$(BOOT)loader32.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(SYS)irq.asm -o ${BUILD}$(KERNEL)$(SYS)irq_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(SYS)isr.asm -o ${BUILD}$(KERNEL)$(SYS)isr_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(FPU)fpu.asm -o ${BUILD}$(KERNEL)$(FPU)fpu_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(MEM)gdt.asm -o ${BUILD}$(KERNEL)$(MEM)gdt_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(MEM)idt.asm -o ${BUILD}$(KERNEL)$(MEM)idt_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(PCI)pci.asm -o ${BUILD}$(KERNEL)$(PCI)pci_asm.o
@${ASSEMBLER} -f coff ${SOURCE}$(KERNEL)$(GFX)gfx.asm -o ${BUILD}$(KERNEL)$(GFX)gfx_asm.o
@${ASSEMBLER} -f coff ${SOURCE}${LIB}math/math.asm -o ${BUILD}${LIB}math/math_asm.o
compile: assemble
@echo Compiling Kernel Sources
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(TEST)test.o -c ${SOURCE}$(KERNEL)$(TEST)test.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)system.o -c ${SOURCE}$(KERNEL)$(SYS)system.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)kernel.o -c ${SOURCE}$(KERNEL)$(SYS)kernel.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)video.o -c ${SOURCE}$(KERNEL)$(SYS)video.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)string.o -c ${SOURCE}$(KERNEL)$(SYS)string.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)isr.o -c ${SOURCE}$(KERNEL)$(SYS)isr.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)irq.o -c ${SOURCE}$(KERNEL)$(SYS)irq.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)time.o -c ${SOURCE}$(KERNEL)$(SYS)time.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)kb.o -c ${SOURCE}$(KERNEL)$(SYS)kb.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)shell.o -c ${SOURCE}$(KERNEL)$(SYS)shell.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(SYS)console.o -c ${SOURCE}$(KERNEL)$(SYS)console.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(MEM)gdt.o -c ${SOURCE}$(KERNEL)$(MEM)gdt.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(MEM)idt.o -c ${SOURCE}$(KERNEL)$(MEM)idt.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(MEM)vmemory.o -c ${SOURCE}$(KERNEL)$(MEM)vmemory.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(MEM)paging.o -c ${SOURCE}$(KERNEL)$(MEM)paging.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(FPU)fpu.o -c ${SOURCE}$(KERNEL)$(FPU)fpu.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(PCI)pci.o -c ${SOURCE}$(KERNEL)$(PCI)pci.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(NET)ne2000.o -c ${SOURCE}$(KERNEL)$(NET)ne2000.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}$(KERNEL)$(GFX)gfx.o -c ${SOURCE}$(KERNEL)$(GFX)gfx.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}${LIB}${MATH}math.o -c ${SOURCE}${LIB}${MATH}math.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}${LIB}${MATH}trig.o -c ${SOURCE}${LIB}${MATH}trig.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}${LIB}${MATH}vector.o -c ${SOURCE}${LIB}${MATH}vector.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}${LIB}${MATH}matrix.o -c ${SOURCE}${LIB}${MATH}matrix.c
@${COMPLIER} @${COMPILER_FLAGS} -o ${BUILD}${LIB}${LANG}compiler.o -c ${SOURCE}${LIB}${LANG}compiler.c
link: assemble compile
@echo Linking Kernel Object Code Files Outputing a Flat Binary
@${LINKER} $(LINKER_FLAGS) -r -Map ${DOCUMENTS}kernel.o.map -nodefaultlibs -nostdlib -V -m i386go32 -T ./cnf/link.ld -o ${BUILD}$(KERNEL)kernel.o
@${LINKER} $(LINKER_FLAGS) -Map ${DOCUMENTS}kernel.bin.map -nodefaultlibs -nostdlib -V -m i386go32 -T ./cnf/link2.ld -o ${BUILD}$(KERNEL)kernel.bin
@rem ${OBJCOPY} -Ibinary -i386 -Obinary -Bi386 ${BUILD}$(KERNEL)kernel.o ${BUILD}$(KERNEL)kernel.bin
create_fat12_image: link
@echo Writing FAT12 Image
@${FAT12_IMAGE_GENERATOR} -c -f ${BUILD}fat12.img -F
@${FAT12_IMAGE_GENERATOR} -m -f ${BUILD}fat12.img -i ${BUILD}$(KERNEL)kernel.bin
@${FAT12_IMAGE_GENERATOR} -m -f ${BUILD}fat12.img -s ${BUILD}$(BOOT)boot.bin
make_distribution: create_fat12_image
@echo Renaming Image
@copy /b "bld\fat12.img" "dst\os.img"
emulate: make_distribution
@echo Running in Emulator
@${EMULATOR} -q -f ${CONFIGURATION}bochconfig.bxrc
@echo Done!
format_disk:
@echo Formating disk in drive A:
@format A:
@echo Done!
make_disk: make_distribution
@echo Writing to Disk
@cd $(WRITER_DIR)
@$(WRITER) -f dst\os.img -d A -n
@echo Done!Can anyone spot why the pointers to the statically defined or annonymously define strings are reported as 0x0000000 when I am in the kernel, causing them to not display after a call to my printf(string,vargs)?
I have diligently searched every post on earth regarding this issue and have not found a statisfactory reason why this might be happening. Some of the suggestion which I have found and have not yeilded a result are:
-.rodata section not defined in linker script, in the .text, .data or stand alone section.
-using the a.out format from NASM and linking this with coff emitted by DJGPP.
-incorrectly defined gdt data segment selector values.
Some possiblities which i am looking into:
-the second linker script links a 16bit aout assembler boot routine with the kernel 32bit coff relocateable object, could the ponters to the strings get mucked up here?
-do i need a second stage boot loader to avoid liking the 16bit bootloader code with the 32bit kernel object? How else could I avoid linking the 16bit code with the 32 bit code.
-The strings which are in the .data section get comipled in to the final kernel binary image and get loaded at 0x0000000 in the code segent of the memory (4gig linear address space), would there be an issue with the .data stuff getting loading into the code segment (can see there would be if i am only reading from the data).
Other than that I am out of ideas. If any one has any please feel free to reply to my post. I will endevour to answer some questions of the newbies. If you require any information other than what I have posted please ask, for example output from objdump.exe, strings.exe etc.
This issue is really hampering my efforts as I cannot declare a statement like printf("something %i\n\r",i); I have to first declare char msg_something[] = "something %i\n\r"; and then do printf(msg_something,i); (i'm tired already, just imaging writing a compiler like that!!!, you are right, its not going to happen unless i can printf("something")).
Any help with this problem would be GREATLY appreciated
[EDIT: Code tags added by Brendan]
