Please help with __attribute__ weak

Please help with __attribute__ weak

[Dimitry Golubovsky]

I need to declare a symbol which is weaker in the executable than in any 
external static or dynamic library.

In other words, the executable provides some fallback function 
implementation (in my example, for "write"). But if the linker or 
dynamic linker resolves it, the symbol definition from an external 
library must be used.

I use:

__f_write_weak_alias(int __fd, __const __ptr_t __buf, size_t __n) 
__attribute__((weak, alias ("write"))); /* alias declaration */

int write(int __fd, __const __ptr_t __buf, size_t __n) {
   printf("Abort\n");
} /* fallback implementation */

But even though "write" is resolved, calling the __f_write_weak_alias 
just prints "Abort" i. e. the symbol "write" was not overridden by the 
library definition.

What is the right way to do this?

Thanks for any advice.

Dimitry Golubovsky
Middletown, CT

Re: Please help with __attribute__ weak

[H. J. Lu]

On Tue, Jul 26, 2005 at 07:19:43AM -0400, Dimitry Golubovsky wrote:
> 
> I need to declare a symbol which is weaker in the executable than in any
> external static or dynamic library.
> 
> In other words, the executable provides some fallback function
> implementation (in my example, for "write"). But if the linker or
> dynamic linker resolves it, the symbol definition from an external
> library must be used.
> 

The weak symbol is different from the normal one only during creating
executable or shared library if it is in a relocatable file. You
can't use weak symbol for your purpose. But you can mark your symbol in
shared library protected.



H.J.

Please help with __attribute__ weak

[Dimitry Golubovsky]

I need to declare a symbol which is weaker in the executable than in any
external static or dynamic library.

In other words, the executable provides some fallback function
implementation (in my example, for "write"). But if the linker or
dynamic linker resolves it, the symbol definition from an external
library must be used.

I use:

__f_write_weak_alias(int __fd, __const __ptr_t __buf, size_t __n)
__attribute__((weak, alias ("write"))); /* alias declaration */

int write(int __fd, __const __ptr_t __buf, size_t __n) {
    printf("Abort\n");
} /* fallback implementation */

But even though "write" is resolved, calling the __f_write_weak_alias
just prints "Abort" i. e. the symbol "write" was not overridden by the
library definition.

What is the right way to do this?

Thanks for any advice.

Dimitry Golubovsky
Middletown, CT