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jump to c++ static function from assemble error?
Posted: Fri Aug 17, 2007 4:58 am
by jinglexy
at the first period of my hobby os, i jump out assemble to c function,
Code: Select all
lidt idt_descr
call start_kernel
cli
start_kernel define as:
Code: Select all
extern "C" void start_kernel(void)
{
CKernel::start_kernel();
}
i think the c function may instead of c++ static function, in the init/main.cpp,
the start process defined as:
Code: Select all
class CKernel
{
public:
static void start_kernel(void);
};
void Ckernel::start_kernel(void)
{
......
}
after assemble, the init/main.o created, i get the Ckernel::start_kernel() function name as:
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readelf -a init/main.o > grep start_kernel
the function name mangling by g++ is "_ZN7CKernel12start_kernel",
then i jump to the kernel as:
Code: Select all
lidt idt_descr
call _ZN7CKernel12start_kernel
cli
when link, an error occur, the link can not find function "_ZN7CKernel12start_kernel", why?
Posted: Fri Aug 17, 2007 5:09 am
by Combuster
you have been mixing CKernel with Ckernel at occasions, which are two completely different things. Try fixing that first
Also, please use
tags. blue on blue is incredibly difficult to read.
(So is white on white 
)
Posted: Fri Aug 17, 2007 5:26 am
by JamesM
You probably don't want to be calling the C++ function immediately anyway. The initial C trampoline code is an ideal place to initialise and destroy global objects as defined in the .ctor and .dtor sections of your binary.
JamesM
Posted: Fri Aug 17, 2007 5:28 am
by jinglexy
hi, i also puzzled what difference of c and c++ static func, how do solve it?
thank you a lot.
Posted: Fri Aug 17, 2007 5:38 am
by os64dev
well did you declare the kernel function extern in you assembly file?
Code: Select all
loader.s
.extern __ZN7CKernel12start_kernelEv;
entry:
call __ZN7CKernel12start_kernelEv;
jmp .
compile with 'as -o loader.o loader.s'
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kernel.cc
class CKernel
{
public:
static void start_kernel(void);
};
void CKernel::start_kernel(void)
{
}
compile with 'g++ -o kernel.o -c kernel.cc'
link together with 'g++ -o test.exe loader.o kernel.o -nostartfiles'
no problems encountered. difference with you btw is leading underscore
Posted: Fri Aug 17, 2007 5:45 am
by jinglexy
in file head.S
.globl _ZN7CKernel12start_kernel
........
call call _ZN7CKernel12start_kernel
make output:
>>>>>> linking: vmjinix
ld -nostdlib -T /home/wyt/source/os/jinix-1.2.1/arch/i386/vmjinix.lds \
-o /home/wyt/source/os/jinix-1.2.1/arch/i386/vmjinix arch/i386/kernel/head.o arch/arch.t drivers/drivers.t fs/fs.t init/init.t ipc/ipc.t kernel/kernel.t lib/lib.t mm/mm.t net/net.t
arch/i386/kernel/head.o(.text+0xe6): In function `second_gdtr':
/home/wyt/source/os/jinix-1.2.1/arch/i386/kernel/head.S:121: undefined reference to `_ZN7CKernel12start_kernel'
make[1]: *** [vmjinix] error 1
make: *** [all] error 2
Posted: Fri Aug 17, 2007 5:46 am
by os64dev
sorry i edited the post: solution above
Posted: Fri Aug 17, 2007 6:07 am
by jinglexy
thank you very much, the problem resolved:
wyt@kdc-media ~/source/os/jinix-1.2.1]$ readelf -a init/main.o | grep start_kernel
22: 00000000 225 FUNC GLOBAL DEFAULT 1 _ZN7CKernel12start_kernel
[wyt@kdc-media ~/source/os/jinix-1.2.1]$ nm init/main.o | grep start_kernel
00000000 T _ZN7CKernel12start_kernelEv
the function read by readelf is truncated,
only "nm" get the correct func name, that's strange of readelf.
Posted: Fri Aug 17, 2007 7:32 am
by JamesM
hi, i also puzzled what difference of c and c++ static func, how do solve it?
thank you a lot.
A C++ static member function is one which is a member of a class, but is called without a "this" pointer. So it does not have access to any member variables of a class instance.
A C (or C++) static global function is one who's symbol
is not exported. So, if you had 2 files:
a.c:
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extern int func();
void main() {
func();
}
b.c:
This would not link, complaining of an undefined symbol - func. If func() was declared without the static modifier, it would link.
JamesM