problems with dlopen

problems with dlopen

[Henning Moll]

Hello!

Why does this code fail with segfault?
I think the problem is that dlopen calls malloc itself? Is that right?
Any suggestions how to fix it?

--snip--
#include <stdlib.h>
#include <dlfcn.h>

static void *(*orig_malloc) (size_t) = 0;

void *
malloc(size_t p)
{
        static int state = 0;
        void * handle;

        switch (state)
        {
                case 0:
                        handle = dlopen("cygwin1.dll", RTLD_NOW);
                        orig_malloc = (void *(*)(size_t)) dlsym (handle, "malloc");
                        state = 1;
                        /*fall through*/
                case 1:
                        return (*orig_malloc) (p);
        }
}

int
main()
{
        return 0;
}

  

--snip--

Best regards,
Henning


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Re: problems with dlopen

[Cliff Hones]

> Why does this code fail with segfault?
> I think the problem is that dlopen calls malloc itself? Is that right?
> Any suggestions how to fix it?

If your suspicion is correct, then simply moving "state = 1" to before
the call of dlopen should do the trick, i.e.:

                case 0:
                        state = 1;
                        handle = dlopen("cygwin1.dll", RTLD_NOW);
                        orig_malloc = (void *(*)(size_t)) dlsym (handle, "malloc");
                        /*fall through*/
-- Cliff

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Re[2]: problems with dlopen

[Henning Moll]

Hallo Cliff,

Friday, December 07, 2001, 5:26:33 PM, you wrote:

> If your suspicion is correct, then simply moving "state = 1" to before
> the call of dlopen should do the trick, i.e.:

>                 case 0:
>                         state = 1;
>                         handle = dlopen("cygwin1.dll", RTLD_NOW);
>                         orig_malloc = (void *(*)(size_t)) dlsym (handle, "malloc");
>                         /*fall through*/
> -- Cliff

You're right, that was an error.
Unfortunately it doesn't solve the problem. Again, the same error
while executing 'dlopen'.
Now i think the problem ist not a recursive call of 'malloc' (for the
moment), because i should be able to detect such recursive behaviour
by setting a breakpoint in my own malloc... Hmm, and there is no
recursion before the segfault.
Sure, after the current problem is removed, dlopen may call malloc to
get some memory. For that purpose i'll try to implement an additional
state which then use a static memory array to provide the requested
memory.

Again, any suggestions?

-- 
Best regards,
Henning


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Re: problems with dlopen

[Christopher Faylor]

On Fri, Dec 07, 2001 at 05:56:43PM +0100, Henning Moll wrote:
>Again, any suggestions?

Look at the cygwin source code?

cgf

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