Accessing static variable from outside

Accessing static variable from outside

[Rajat Jain]

Hi,

I understand that this is off-topic, but still if some one has any ideas ...

I have a global variable that is defined static in an object file (say
1.o). Now I want to be able to get the value of this variable in
ANOTHER object file (say 2.o) without changing the source of 1.c.

Any ideas, anyone? I know that as per C, this is not possible. But may
be some clever hack?

Thanks,

Rajat
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Re: Accessing static variable from outside

[Adrian Bunk]

On Sat, Jun 16, 2007 at 07:38:07AM +0530, Rajat Jain wrote:
> Hi,
>
> I understand that this is off-topic, but still if some one has any ideas 
> ...
>
> I have a global variable that is defined static in an object file (say
> 1.o). Now I want to be able to get the value of this variable in
> ANOTHER object file (say 2.o) without changing the source of 1.c.
>
> Any ideas, anyone? I know that as per C, this is not possible. But may
> be some clever hack?

Depending on how the variable gets used the compiler might even 
completely optimize it away.

> Thanks,
>
> Rajat

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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Re: Accessing static variable from outside

[tejas khatiwala]

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AFAIK one way to be able to access a static variable is using dynamic
linking lodader. u can read man pages of dlopen() and family. and here is
example of its usage http://www.slimy.com/~jleonard/src/dlopen.html

/tejas

On 6/15/07, Rajat Jain <rajat.noida.india@gmail.com> wrote:
>
> Hi,
>
> I understand that this is off-topic, but still if some one has any ideas
> ...
>
> I have a global variable that is defined static in an object file (say
> 1.o). Now I want to be able to get the value of this variable in
> ANOTHER object file (say 2.o) without changing the source of 1.c.
>
> Any ideas, anyone? I know that as per C, this is not possible. But may
> be some clever hack?
>
> Thanks,
>
> Rajat
>
> --
> To unsubscribe from this list: send an email with
> "unsubscribe kernelnewbies" to ecartis@nl.linux.org
> Please read the FAQ at http://kernelnewbies.org/FAQ
>
>

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Re: Accessing static variable from outside

[Erik Mouw]

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A: http://en.wikipedia.org/wiki/Top_post
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A: Because it messes up the order in which people normally read text.
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A: Top-posting.
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A: No.
Q: Should I leave quotations after my reply?

On Sat, Jun 16, 2007 at 11:36:43AM -0500, tejas khatiwala wrote:
> AFAIK one way to be able to access a static variable is using dynamic
> linking lodader. u can read man pages of dlopen() and family. and here is
> example of its usage http://www.slimy.com/~jleonard/src/dlopen.html

The example doesn't apply:

- - dlopen() is a userspace function and can't be used in kernel
- - dynamic linking can only be used to link exported (i.e. non-static)
  symbols

Like Adrian Bunk already explained: there are dirty tricks to get the
address of a static variable, but they will all fail when the compiler
decides to optimise the variable away (which it is completely free to
do because the "static" keyword *guarantees* that the variable will not
be used outside that particular compilation unit).


Erik

- -- 
They're all fools. Don't worry. Darwin may be slow, but he'll
eventually get them. -- Matthew Lammers in alt.sysadmin.recovery
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