Re: [Linux-ia64] patching sys_call_table from a module

[Don Dugger <n0ano@valinux.com>]

Chas-

Your problem is that, in IA64, a pointer to a function does not point
directly to the function itself.  Instead it points to a data structure
where the first element truly points to the function and the second
element contains the GP value for the function.

Changing your code to something like:

  int __init
  mysyscall_init(void)
  {
        struct foo {
            long addr;
            long gp;
        } fp;

        printk("hello world\n");
        saved_syscall = sys_call_table[__NR_afs_syscall - 1024];
        fp = (struct foo *)afs_syscall;
        sys_call_table[__NR_afs_syscall - 1024] = fp->addr;
        return 0;
  }

should accomplish what you want.  (I think there are some magic C
macros that will break a function pointer into it's component pieces
but I don't know what they are, I just do it the hard way :-)

On Tue, Jul 03, 2001 at 04:03:23PM -0400, chas williams wrote:
> i wrote a little example to illustrate my problem.  its attached at the
> bottom.  if i make a syscall(__NR_afs_syscall, ...) i get the following:
> 
> pts[2437]: Bad break 104
> 
> psr : 0000101008026018 ifs : 8000000000000008 ip  : [<a0000000000344b0>]
> unat: 0000000000000000 pfs : 0000000000000089 rsc : 0000000000000003
> rnat: 40000000000bb190 bsps: e0000000044157b0 pr  : 000000000001015b
> ldrs: 0000000000000000 ccv : 0000000000000000 fpsr: 0009804c0270033f
> b0  : e000000004415ce0 b6  : e000000004402f60 b7  : e0000000044157b0
> f6  : 1003e0000000000000020 f7  : 1003e0000000000000010
> f8  : 1003e0000000000000006 f9  : 10002a000000000000000
> r1  : e000000004a12b20 r2  : 0000000000000000 r3  : 00000000000000ff
> r8  : e00000002facff00 r9  : 0000000000000000 r10 : ffffffffffffffff
> r11 : 600000000000c3b8 r12 : e00000002facfe60 r13 : e00000002fac8000
> r14 : e000000000000000 r15 : e000000004415ce0 r16 : e00000002facfe70
> r17 : e00000002facfe78 r18 : 00001013080a6010 r19 : 20000000001e1bb0
> r20 : 0000000000000000 r21 : 4000000000000e98 r22 : 600000000005ec20
> r23 : 600000000005ed28 r24 : 0000000000005540 r25 : 2000000000293f90
> r26 : 600000000005ed28 r27 : 0000000000000000 r28 : 0000000000000040
> r29 : 0000000000000000 r30 : 0000000000000008 r31 : 0000000000000000
> r32 : 0000000000000000 r33 : 0000000000000000 r34 : 0000000000000000
> r35 : 0000000000000000 r36 : 0000000000000000 r37 : 0000000000000000
> r38 : 0000000000000000 r39 : 0000000000000000
> 
> Call Trace: [<e00000000441a080>] sp=0xe00000002facfa50 bsp=0xe00000002fac8ec8
> [<e00000000441a840>] sp=0xe00000002facfc10 bsp=0xe00000002fac8e70
> [<e00000000442b830>] sp=0xe00000002facfc30 bsp=0xe00000002fac8e48
> [<e00000000442bb00>] sp=0xe00000002facfc30 bsp=0xe00000002fac8e28
> [<e000000004415d00>] sp=0xe00000002facfcc0 bsp=0xe00000002fac8e28
> [<a0000000000344b0>] sp=0xe00000002facfe60 bsp=0xe00000002fac8de0
> [<e000000004415ce0>] sp=0xe00000002facfe60 bsp=0xe00000002fac8dd8
> 
> what am i doing wrong or cant i do this?
> 
> /* mysyscall.c 
>   
> % cc -O2 -fomit-frame-pointer -fno-strict-aliasing -pipe -ffixed-r13 -mfixed-rangeñ0-f15,f32-f127 -falign-functions2 -mb-step -D__KERNEL__ -DKERNEL -D_KERNEL -DMODULE -c mysyscall.c
> 
> */
> 
> #include <linux/config.h>
> #include <linux/module.h>
> #include <linux/version.h>
> #include <linux/kernel.h>
> #include <linux/errno.h>
> #include <linux/types.h>
> #include <linux/string.h>
> #include <linux/init.h>
> #include <sys/syscall.h>
> 
> extern long sys_call_table[];
> static long saved_syscall;
> 
> asmlinkage long 
> afs_syscall(long arg0, long arg1, long arg2, long arg3,
>           long arg4, long arg5, long arg6, long arg7, long stack)
> {
>         struct pt_regs *regs = (struct pt_regs *) &stack;
> 	
> 	printk("afs_syscall()\n");
> 
> 	return 0;
> }
> 
> int __init
> mysyscall_init(void)
> {
> 	printk("hello world\n");
> 	saved_syscall = sys_call_table[__NR_afs_syscall - 1024];
> 	sys_call_table[__NR_afs_syscall - 1024] = (long) afs_syscall;
> 	return 0;
> }
> 
> void __exit
> mysyscall_exit(void)
> {
> 	printk("goodbye cruel world\n");
> 	sys_call_table[__NR_afs_syscall - 1024] = saved_syscall;
> }
> 
> module_init(mysyscall_init);
> module_exit(mysyscall_exit);
> 
> 
> _______________________________________________
> Linux-IA64 mailing list
> Linux-IA64@linuxia64.org
> http://lists.linuxia64.org/lists/listinfo/linux-ia64

-- 
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
n0ano@valinux.com
Ph: 303/938-9838