After editing compiler options, kernel is 10x size.

[austanss]

For my 100th commit to my GitHub repo, I am revamping my Makefile, re-ordering my source directory, and optimizing my code.
Also, I was planned on using a cross-compiler. (The cross-compiler has built libgcc with -mno-red-zone).

You can find my old Makefile, which compiled my kernel to about 175KiB (with debug symbols) in my microCORE link in signature.
This is my new Makefile:

Code: Select all

SRCDIR 	= src
BINDIR  = bin
OBJDIR  = bin/obj

CXXSRC 	= $(call rwildcard,$(SRCDIR),*.cxx)
ASMSRC 	= $(call rwildcard,$(SRCDIR),*.asm)
LDS		= microCORE.lds

OBJS 	= $(patsubst $(SRCDIR)/%.cxx, $(OBJDIR)/%.cxx.o, $(CXXSRC))
OBJS 	+= $(patsubst $(SRCDIR)/%.asm, $(OBJDIR)/%.asm.o, $(ASMSRC))

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

CXXC 	= x86_64-elf-gcc
ASMC 	= nasm

CFLAGS 	= -ffreestanding -I$(SRCDIR) -std=gnu++17 -gdwarf -O0 -mno-red-zone -msse2 -fno-threadsafe-statics
LFLAGS  = -ffreestanding -nostdlib -mno-red-zone -lgcc -T $(LDS)
AFLAGS	= -f elf64 -g -F dwarf 

.DEFAULT-GOAL = all

$(OBJDIR)/%.cxx.o: $(SRCDIR)/%.cxx
	@ echo "=={+-}===>>> COMPILING $^"
	@ mkdir -p $(@D)
	@ $(CXXC) $(CFLAGS) -c $^ -o $@

$(OBJDIR)/%.asm.o: $(SRCDIR)/%.asm
	@ echo "=={+-}===>>> ASSEMBLING $^"
	@ mkdir -p $(@D)
	@ $(ASMC) $(AFLAGS) $^ -o $@

kernel: $(OBJS)
	@ echo "=={+-}===>>> LINKING bin/microCORE.kernel"
	@ $(CXXC) $(LFLAGS) $(OBJS) -o $(BINDIR)/microCORE.kernel

all: kernel

clean:
	@ rm -rf bin

Whereas before my kernel compiled to about 175KiB with debug symbols, now my kernel is 1.1MB without debug symbols, and 1.2MB with.
I ensured that I wasn't linking duplicate objects.

This is important because my kernel is supposed to be small and performant, not bloated.
Also, if I'm taking up 10x the space with 1x the code, that is a waste of memory.

Does anyone know why this is occurring?

EDIT: I realized that the linker script is also important here:

Code: Select all

ENTRY(kernel_entry)

SECTIONS
{
	. = 1M;

	_kernel_start = .;
	
	.stivalehdr : 
	{
        KEEP(*(.stivalehdr))
    }

	.text :
	{
		*(.text .text.*)
	}

	.rodata :
	{
		*(.rodata .rodata.*)
	}

	.data :
	{
		*(.data.rel.ro.local*) *(.data.rel.ro .data.rel.ro.*) *(.data.*)
	}

	.bss :
	{
		*(.bss .bss.*);
	}

	. = ALIGN(4K);

	.userspace :
	{
		*(.userspace);
	}
	
	_kernel_end = .;
}

This is an edited version, the original version that did not raise issues is in my GitHub.

[nexos]

Are you passing -z max-page-size=0x1000 to the linker? If not, you should.

[austanss]

Are you passing -z max-page-size=0x1000 to the linker? If not, you should.

Thanks! That fixed the issue! I wasn't using that parameter before, I don't know why it works now.

With all the editing I did, I cut down the size of my kernel 50KiB! That's great!

[nexos]

That's because by default, the linker aligns sections on a 4MB boundary. This means sections must be expanded to meet this requirement.