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"ifstream" not working in kernel, even when I use g++

Posted: Sun Aug 01, 2021 7:04 pm
by amandude
I am trying to read/write to a .txt file using "fstream" to store permanent data, even if the system reboots.
The problem is that when I go to compile, it says:

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kernel.cpp:(.text+0x52): undefined reference to `std::basic_ifstream<char, std::char_traits<char> >::basic_ifstream()'
ld: kernel.cpp:(.text+0x6d): undefined reference to `std::basic_ifstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode)'
make: *** [Makefile:47: link] Error 1
I tried using g++ instead of gcc, but it still did not work.

Does anyone know how to fix this?

PS: I am following off of this tutorial: ... ead/kernel

Here is the code:


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GNUEFI = ../gnu-efi
LDS = kernel.ld
CC = g++
ASMC = nasm
LD = ld

CFLAGS = -ffreestanding -fshort-wchar -mno-red-zone -fno-exceptions
LDFLAGS = -T $(LDS) -static -Bsymbolic -nostdlib

SRCDIR := src
OBJDIR := lib
BOOTEFI := $(GNUEFI)/x86_64/bootloader/main.efi

rwildcard=$(foreach d,$(wildcard $(1:=/*)),$(call rwildcard,$d,$2) $(filter $(subst *,%,$2),$d))

SRC = $(call rwildcard,$(SRCDIR),*.cpp)  
ASMSRC = $(call rwildcard,$(SRCDIR),*.asm)  
OBJS = $(patsubst $(SRCDIR)/%.cpp, $(OBJDIR)/%.o, $(SRC))
OBJS += $(patsubst $(SRCDIR)/%.asm, $(OBJDIR)/%_asm.o, $(ASMSRC))
DIRS = $(wildcard $(SRCDIR)/*)

kernel: $(OBJS) link

$(OBJDIR)/interrupts/interrupts.o: $(SRCDIR)/interrupts/interrupts.cpp
	@ echo !==== COMPILING $^
	@ mkdir -p $(@D)
	$(CC) -mno-red-zone -mgeneral-regs-only -ffreestanding -c $^ -o $@

$(OBJDIR)/%.o: $(SRCDIR)/%.cpp
	@ echo !==== COMPILING $^
	@ mkdir -p $(@D)
	$(CC) $(CFLAGS) -c $^ -o $@
$(OBJDIR)/%_asm.o: $(SRCDIR)/%.asm
	@ echo !==== COMPILING $^
	@ mkdir -p $(@D)
	$(ASMC) $(ASMFLAGS) $^ -f elf64 -o $@
	@ echo !==== LINKING
	$(LD) $(LDFLAGS) -o $(BUILDDIR)/kernel.elf $(OBJS)

	@mkdir $(BUILDDIR)
	@mkdir $(SRCDIR)
	@mkdir $(OBJDIR)

	dd if=/dev/zero of=$(BUILDDIR)/$(OSNAME).img bs=512 count=93750
	mformat -i $(BUILDDIR)/$(OSNAME).img -f 1440 ::
	mmd -i $(BUILDDIR)/$(OSNAME).img ::/EFI
	mmd -i $(BUILDDIR)/$(OSNAME).img ::/EFI/BOOT
	mcopy -i $(BUILDDIR)/$(OSNAME).img $(BOOTEFI) ::/EFI/BOOT
	mcopy -i $(BUILDDIR)/$(OSNAME).img startup.nsh ::
	mcopy -i $(BUILDDIR)/$(OSNAME).img $(BUILDDIR)/kernel.elf ::
	mcopy -i $(BUILDDIR)/$(OSNAME).img $(BUILDDIR)/zap-light16.psf ::

	qemu-system-x86_64 -drive file=$(BUILDDIR)/$(OSNAME).img -m 256M -cpu qemu64 -drive if=pflash,format=raw,unit=0,file="$(OVMFDIR)/OVMF_CODE-pure-efi.fd",readonly=on -drive if=pflash,format=raw,unit=1,file="$(OVMFDIR)/OVMF_VARS-pure-efi.fd" -net none


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#include <fstream>
#include <stdint.h>
using namespace std;

#include "kernelUtil.h"
#include "eif.h"
#include "userinput/keyboard.h"
#include "prepare_os/prepare-os.h"
#include "prepare_os/frame_handler.h"
#include "ahci/ahci.h"

extern "C" void _start(BootInfo* bootInfo){

    KernelInfo kernelInfo = InitializeKernel(bootInfo);


    IntInfo defaultInfo = GetDefaultIntfSettings();

    // this is just to make the interface (basically just plotting pixels)


    // Here is where I do the file opening

    ifstream myFile;

    // I am just testing this out to see if it compiles,  "info/username.txt");

        asm ("hlt");
Thanks for your help! :D

Re: "ifstream" not working in kernel, even when I use g++

Posted: Sun Aug 01, 2021 9:51 pm
by Octocontrabass
"ifstream" is part of the C++ standard library. You need to port the C++ standard library to your OS before you can use anything in it.

It's also a good idea to use a cross-compiler. (I personally would also get rid of GNU-EFI and use plain UEFI headers with a cross-compiler, but that's just me.)

Don't trust OS development tutorials. They're full of bugs.