OSDev.org

Posted: **Fri Jun 24, 2011 1:49 pm**

Hello OS Developers, I'm Lionel, and I'm new to the forums.
I was following the Bran's Kernel Development Tutorial, and I got the first part of the tutorial done.(Creating start.asm and compiling it into kernel.bin). I build a cross compiler(i586-elf). The problem is when I try to compile the kernel with the file build.sh(start.asm is renamed boot.asm)...

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echo "Building Kernel..."
echo "Assembling..."
nasm -f aout -o boot.o boot.asm
echo "Compiling..."
i586-elf-gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -c -o main.o main.c
echo "Linking output to kernel.bin"
ld -T link.ld -o kernel.bin boot.o main.o
echo "Finished Building Kernel!"

I get this:

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corwin@vinneticus:~/Desktop/iKatos$ ./build.sh
Building Kernel...
Assembling...
Compiling...
main.c:2:43: error: unknown type name 'size_t'
main.c:10:36: error: unknown type name 'size_t'
main.c:17:67: error: unknown type name 'size_t'
main.c:24:1: error: unknown type name 'size_t'
main.c: In function 'strlen':
main.c:26:5: error: unknown type name 'size_t'
main.c: At top level:
main.c:42:6: warning: return type of 'main' is not 'int' [-Wmain]
Linking output to kernel.bin
ld: cannot find main.o: No such file or directory
Finished Building Kernel!

I found size_t is in the file stddef.h , but gcc can't find it.
I don't know what to do, Could someone help me please?
~Lionel

Posted: **Fri Jun 24, 2011 2:09 pm**

Define it yourself, or possibly include stddef.h

When building your kernel, files arent automaticly included (because they would probably cause lots of issues)

Posted: **Fri Jun 24, 2011 2:26 pm**

I can't include stddef.h because it complains about there being duplicates of memcpy and other functions.

Posted: **Fri Jun 24, 2011 2:44 pm**

Yes, to Avoid Startup Code and os-dependent functions.
Edit: Now there is a new error that happens:

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main.c:2:7: error: conflicting types for 'memcpy'
system.h:5:23: note: previous declaration of 'memcpy' was here
main.c:10:7: error: conflicting types for 'memset'
system.h:6:23: note: previous declaration of 'memset' was here
main.c:17:17: error: conflicting types for 'memsetw'
system.h:7:24: note: previous declaration of 'memsetw' was here
main.c:24:14: error: conflicting types for 'strlen'
system.h:8:12: note: previous declaration of 'strlen' was here
main.c:42:6: warning: return type of 'main' is not 'int' [-Wmain]

Posted: **Fri Jun 24, 2011 3:17 pm**

So? The error messages are pretty clear, aren't they?

One, what is this system.h?

Two, why do the types differ?

(Rethorical question warning.)

Posted: **Fri Jun 24, 2011 3:26 pm**

If you ever want to work with gcc builtins you should define:

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typedef long unsigned int size_t;

This works on 32bit, using unsigned int you may get warning for incompatible memcpy and such.
I'm not sure for 64-bit size_t, perhaps unsigned long long..

Posted: **Fri Jun 24, 2011 3:36 pm**

Thanks bluemoon! I figured it out,. The tutorial code has differing types, and ubuntu doesn't like that. I made it work. Thank you everyone!

Posted: **Fri Jun 24, 2011 3:54 pm**

berkus wrote:Do you know why you have built a cross-compiler?

Lionel wrote:The tutorial code has differing types, and ubuntu doesn't like that.

I.e., "no".

Posted: **Fri Jun 24, 2011 4:01 pm**

Lionel wrote:Thanks bluemoon! I figured it out,. The tutorial code has differing types, and ubuntu doesn't like that. I made it work. Thank you everyone!

The blame is not to ubuntu.

gcc provide some useful built-ins like memcpy, when generate code it optimize and decided emit the build-in code, or to emit a library call.
so your fall-back version of the memcpy, etc should have exactly same prototype with the built-ins, otherwise gcc tell you a warning for such case.

So, to solve the problem you may:
1. write the function and types so they match exactly the builtin functions.
2. disable gcc builtin by -fno-builtin-memcpy or -fno-builtin (disable all builtin)
3. ignore the warnings and take your own risk.

Posted: **Sat Jun 25, 2011 12:54 am**

Lionel wrote:Yes, to Avoid Startup Code and os-dependent functions.
Edit: Now there is a new error that happens:

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main.c:2:7: error: conflicting types for 'memcpy'
system.h:5:23: note: previous declaration of 'memcpy' was here
main.c:10:7: error: conflicting types for 'memset'
system.h:6:23: note: previous declaration of 'memset' was here
main.c:17:17: error: conflicting types for 'memsetw'
system.h:7:24: note: previous declaration of 'memsetw' was here
main.c:24:14: error: conflicting types for 'strlen'
system.h:8:12: note: previous declaration of 'strlen' was here
main.c:42:6: warning: return type of 'main' is not 'int' [-Wmain]

I'm sure gcc generates a warning 'incompatible implicit declaration of built-in function '.....', if you try to use built-in functions without including the corresponding header files. So I believe the problem here is, either the function is being used without first declaring the function prototypes or, the function prototypes have been declared twice with incompatible types.

OSDev.org

No type size_t?

No type size_t?

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