how to get function pointer?

[posman]

Hi.

How can I get address of a function where the name of that function is in a variable?
Look: right now I can get the address of a function with any of this:

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addr = &myfunc;
addr = (unsigned int *)myfunc;

I don't know if there is a big difference between those two lines, but both work.
But that is not the problem. I want to know if is it possible to get the address of myfunc if the name is in a variable. What I want to do is to get the address of several functions in a loop. So I want to have those function names in an array.

Is it possible?

[earlz]

Do you mean like an array of function pointers?

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typedef void (*MyFunctionType)(int);

MyFunctionType fun_array[100];

...
void foo(int n){}

....
fun_array[0]=&foo;

[CodeCat]

From what I've seen, function names are similar to array names in that using the function's name bare, without following parentheses, turns it into a pointer to that function.

Therefore,

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addr = (unsigned int *)myfunc;

should be read as

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addr = (unsigned int *)&myfunc;

I don't recommend casting a function pointer to a scalar pointer, though.

[Solar]

Do I understand correctly that you have an array of char * holding several function names, and want to retrieve the function pointer for each of them?

Sorry, no luck. At least not without third party help - the standard doesn't hold any tricks to that end that I am aware of.

[posman]

Thank you all

[CodeCat]

If you're using C++, then std::map might be useful.

[Solar]

How do you figure?

He can't get the function pointers. So he doesn't have anything to store in the map, either...

[Combuster]

I'd try to do some incremental linking (shove everything but the symbol table into one object file), objdump the .text section, run some formatting script to create a .asm file with the symbol table, then assemble it to finally link that together with the intermediate version to complete the binary.

[DeletedAccount]

I also do not think there is a standard way to do this , But you can always check the compiler documentation for functions that dump the compilers internal symbol tables , which may be created for debugging purposes.But i guess there is no easy way out , But why would you actually want to do such a thing ? Most of the problems of the above nature can be easily solved using a state machine sort of construct .


Regards
Sandeep

[eddyb]

I'd try to do some incremental linking (shove everything but the symbol table into one object file), objdump the .text section, run some formatting script to create a .asm file with the symbol table, then assemble it to finally link that together with the intermediate version to complete the binary.

I think it's simpler... it's called symbols tables and I saw it in some OS...
Oh, yes: use nm(a command from binutils) to list the symbols. this is an example of output:

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00001000 A PageSize
00100000 A PhysBase
0010000c A __phys_start
c0000000 A VirtBase
c0100000 A __text_start
c0100000 t mb_header
c010000c T _start

then, make some script that make a symbol table(it's relative simple, because of the format: address type name). then add it to your kernel. then, use it to find the address of some function, knowing the function's name;)

[CodeCat]

I think you can get the same result by asking ld for a link map.

[Combuster]

great, whe have three ways doing exactly the same thing