GDB Qemu debugging symbols

[therll]

My kernel compiles correctly in debug mode using

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i686-elf-gcc -g -T link.ld -o myos.bin -ffreestanding -O2 -nostdlib start.o main.o scrn.o gdt.o idt.o isrs.o irq.o timer.o kb.o

and boots in Qemu. However when I debug using GDB through

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target remote localhost:1234

, loading my bin file as the GDB symbol file returns an error:

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can't read symbols: File format not recognized.

I'm following http://wiki.osdev.org/Kernel_Debugging# ... _with_Qemu and I think the problem might be that my kernel isn't an elf file but I'm not sure how to make it an elf file or extract the symbols from this binary file. What am I doing wrong?

[turboscrew]

If you first produce an ELF then make bin from it, load the bin into the qemu, but the ELF in gdb before the "target remote"-command.

[therll]

But how do I produce one big ELF from all the little compiled .o ELF files?

[therll]

Ok I figured it out

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objdump -i

lists the available formats and the .ld linker script has an OUTPUT_FORMAT property which can be changed to elf32-i386 and then the symbols load just fine!

[max]

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can't read symbols: File format not recognized.

I'm following http://wiki.osdev.org/Kernel_Debugging# ... _with_Qemu and I think the problem might be that my kernel isn't an elf file but I'm not sure how to make it an elf file or extract the symbols from this binary file. What am I doing wrong?

You must make sure that GDB understands the object format for your target platform. You can simply compile GDB from sources to get one specific for your target platform by doing the same as when you compiled your cross compiler (by adding the "--target" flag to configure).


EDIT:

lists the available formats and the .ld linker script has an OUTPUT_FORMAT property which can be changed to elf32-i386 and then the symbols load just fine!

I don't think that you really want that. You made a cross-compiler that compiles binaries for i686, and now you're linking them as i386? That's why you should make a cross-gdb (as described above), because it is able to read your target platforms object format.

[turboscrew]

If there is i686-elf-gcc, there is probably i686-elf-objdump too?