------- Additional Comments From cburgess at qnx dot com 2009-03-26 13:40
-------
For some reason attachments don't work for me, here are the example source
files...
a.c:
#include <a.h>
int main(void)
{
fptr *fp;
/*
* Here we call function(), which initially selects a traditional
* abicalls stub
*/
function();
/* We show as this function to give us the address of function(),
* however the linker is not aware that the address of function() will
* be referenced within the shared object
*/
set_function_address(&fp);
/* when we now as this funtion to invoke our function pointer, it does
* so from the GOT context of b.so, and thus if it transfer into an
* abicalls stub it will load the incorrect got entry (ie that from
* b.so rather a) and havoc will ensue!
*/
invoke_function(fp);
#if 0
/* But if this code is enabled, the reference to the address of function()
* causes a PLT to be used, and the address of the PLT becomes
* the canonical address of function()
*/
fp = function;
#endif
return 0;
}
a.h:
typedef void (fptr)(void);
extern void function(void);
extern void invoke_function(fptr *f);
extern void set_funtion_address(fptr **f);
b.c:
#include <a.h>
void function(void)
{
}
void set_function_address(fptr **fp)
{
*fp = function;
}
void invoke_function(fptr *fp)
{
(fp)();
}
Makefile:
QCC=env QNX_TARGET=/home/cburgess/qssl/stage qcc -V4.3.3,gcc_ntomipsbe -I .
all: a b.so
clean:
rm -f a b.so *.o
a.o: a.c
$(QCC) -g -c a.c
b.o: b.c
$(QCC) -g -shared -c b.c
a.s:
$(QCC) -S a.c
a: a.o b.so
$(QCC) -o a a.o b.so
b.so: b.o
$(QCC) -shared -o b.so -Wl,-soname=b.so b.o
--
http://sourceware.org/bugzilla/show_bug.cgi?id=10009
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