cfenollosa_os-tutorial/23-fixes

Concepts you may want to Google beforehand: XX

Goal: Fix miscellaneous issues with our code

The OSDev wiki has a section which describes some issues with JamesM's tutorial. Since we followed his tutorial for lessons 18-22 (interrupts through malloc), we'll need to make sure we fix any of the issues before moving on.

1. Wrong CFLAGS

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We add -ffreestanding when compiling .o files, which includes kernel_entry.o and thus kernel.bin and os-image.bin.

Before, we disabled libgcc (not libc) through the use of -nostdlib and we didn't re-enable it for linking. Since this is tricky, we'll delete -nostdlib

-nostdinc was also pased to gcc, but we will need it for step 3.

2. kernel.c main() function

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Modify kernel/kernel.c and change main() to kernel_main() since gcc recognizes "main" as a special keyword and we don't want to mess with that.

Change boot/kernel_entry.asm to point to the new name accordingly.

To fix the i386-elf-ld: warning: cannot find entry symbol _start; defaulting to 0000000000001000 warning message, add a global _start; and define the _start: label in boot/kernel_entry.asm.

3. Reinvented datatypes

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It looks like it was a bad idea to define non-standard data types like u32 and such, since C99 introduces standard fixed-width data types like uint32_t

We need to include <stdint.h> which works even in -ffreestanding (but requires stdlibs) and use those data types instead of our own, then delete them on type.h

<stddef.h> to provide size_t

5. Missing functions

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6. Interrupt handlers

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• also cli, sti in interrupt handlers

7. Structs and attributes

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8. Improperly aligned kmalloc

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