[parisc-linux] more on canonicalize_funcptr_for_compare

[Randolph Chung <randolph@tausq.org>]

The latest glibc on hppa (2.3.1-17) was compiled with a gcc-3.2 which
has the __canonicalize_funcptr_for_compare patch backported from gcc-3.3
... with this new version, some programs will die on startup (e.g. vim).
I traced to a segfault in __canonicalize_funcptr_for_compare. 

The testcase below illustrates the problem:

=====
typedef void (*func_t)(void);

#define N ((func_t)2)

void foo(void) {};

int main(int argc, char **argv)
{
        return (foo == N);
}
=====

this program segfaults when run with:

(gdb) run
Starting program: /home/tausq/sig

Program received signal SIGSEGV, Segmentation fault.
0x00010530 in __canonicalize_funcptr_for_compare ()
(gdb) bt
#0  0x00010530 in __canonicalize_funcptr_for_compare ()
#1  0x000104bc in main (argc=1, argv=0xfaf001b8) at sig.c:9

it seems like the 2 in the constant (N) confuses the comparision
routine. If I change it to 1, everything is ok.... I don't really
understand this tho, because the code for __c_f_f_c has something like:

if ((int) fptr == -1 || (unsigned int) fptr < 4096 || !((int) fptr & 2))
    return (unsigned int) fptr;

so, why doesn't that match the second || case and exit?  (gdb
disassmbly shows that the code tries to dereference the fptr argument
and segfaults)

randolph
-- 
Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports
http://www.tausq.org/