Extern from GCC

[Tolga]

Hi people. I wrote isr codes in assembly file like that;

isr0:
pusha
push fs
push gs
push ds
push es

extern _isr0_code
call _isr0_code

pop es
pop ds
pop gs
pop fs
iret

and i write isr0_code to c file;

void isr0_code()
{}

But there is a problem. When am i linking files, linker showing "undefined reference to _isr0_code". But extern command running with kernel "main" function like that;

extern _main
call _main

What is the matter? ???

[pini]

You can check the object file in which isr0_code is compiled in to see if the symbol is available and under which name with 'objdump'.

Maybe you did declare this symbol as static ?

[Solar]

Another possibility is that your GCC doesn't prefix C function names with underscores. (This is configuration-dependent.) Again, objdump helps.

[Tolga]

I used objdump as;

objdump -t kernel.o

-T = Display the contents of the symbol table(s)

it is showing;

... _main
... _Z11isr0_codev

How can i do _Z11isr0_codev same _isr0_code?

[dc0d32]

Code: Select all

//no mangling for this function
extern "C" void isr0_code();

void isr0_code()
{
...
}

that should work !

[Tolga]

Hey ok, this is working. Thanks.

[guest]

C++ encodes the return type and parameter types into the function names, to link against them from assembly you will need to declare the function as extern "C", use C source files or find the mangled name and explicitly link against the mangled version.

[Solar]

Be aware that there are differences between C and C++. You are compiling your code as C++, which might not be what you intended to do. (For example, C++ does not know about type "long long"...)