Date: Tue, 17 Nov 1998 09:38:37 -0700 From: Nate Williams <nate@mt.sri.com> To: Thomas David Rivers <rivers@dignus.com> Cc: hackers@FreeBSD.ORG, nate@mt.sri.com Subject: Re: Wrapping a function Message-ID: <199811171638.JAA24053@mt.sri.com> In-Reply-To: <199811171348.IAA11670@lakes.dignus.com> References: <199811170517.WAA22627@mt.sri.com> <199811171348.IAA11670@lakes.dignus.com>
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> > Does anyone have an easy way of 'wrapping' an already existing library
> > function so that any programs linked against your .o will call your
> > function, but so your function can call the 'real' library function?
> >
> > Example:
> >
> > my_malloc.c:
> >
> > void *malloc(size_t size)
> > {
> > void *ret;
> >
> > printf("Calling malloc\n");
> > ret = REALMALLOC(size);
> > printf("Leaving malloc\n");
> > return ret;
> > }
> >
>
> I don't know about our linker (gnu-ld) - but many UNIX linkers (and other
> systems as well) have a way to re-name identifiers.
>
> The standard trick would be to pre-link the malloc code from the library;
> renaming the malloc entry there - to say, MALLOC. (ld -r is how you
> prelink.)
>
> Then, you can link your code with that.
Unfortunately, the symbol exists in a shlib, so it must use the same
symbol name as the library since sometimes the shlib exists, and other
times it doesn't. :(
(Don't ask, it's not my code but the JDK. They get around this problem
in Solaris by being aware that dlsym happens to be a simple C function
that calls _dlsym, so in the JDK they call _dlsym directly and hope
no-one else is aware of this feature.)
Sounds like I'll just not be able to wrap those functions. :(
Nate
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