Basic C/C++ (Was: 1.5.10: problems relocating structures with function pointers)
Rolf Campbell
Endlisnis@mailc.net
Wed Jul 21 17:16:00 GMT 2004
Justin Schoeman wrote:
> I have discovered what may be a bug in the linker/relocater in cygwin
> (or, more likely, I am doing something stupid again).
>
> When I use a structure containing function pointers, and this structure
> is placed in an archive, then the function pointer becomes NULL. As an
> example, compile the attached files as follows:
>
> gcc -O2 -Wall -c inc.c
> ar rsvc inc.a inc.c
> gcc -O2 -Wall -o test test.c inc.a
>
> Executing test.exe prints 0x0 (the address of the function cointained in
> the structure), and subsequently segfaults.
>
> Relinking with
>
> gcc -O2 -Wall -o test test.c inc.o
>
> produces a binary that works correctly.
>
> It seems that once the object file is archived, the dynamic loader
> losses the capability of correctly assigning the function addresses?
>
> Any help would be greatly appreciated.
>
> TIA,
> -justin
>
>
> ------------------------------------------------------------------------
>
> #include <stdio.h>
>
> static void junk(void)
> {
> fprintf(stderr, "JUNK!\n");
> }
>
> struct js {
> void (*junk)(void);
> };
>
> const struct js jsi = { junk };
>
>
> ------------------------------------------------------------------------
>
> #include <stdio.h>
>
> struct js {
> void (*junk)(void);
> };
>
> struct js jsi;
extern struct js jsi;
^^^^^^
>
> int main(void)
> {
> fprintf(stderr, "%p\n", jsi.junk);
> jsi.junk();
> return 0;
> }
>
>
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