Helge,
+unsigned long return_address(unsigned int level)
+{
+ struct unwind_frame_info info;
+ struct pt_regs r;
+ unsigned long sp;
+
+ /* initialize unwind info */
+ asm volatile ("copy %%r30, %0" : "=r"(sp));
+ memset(&r, 0, sizeof(struct pt_regs));
+ r.iaoq[0] = (unsigned long) current_text_addr();
+ r.gr[2] = (unsigned long) __builtin_return_address(0);
+ r.gr[30] = sp;
+ unwind_frame_init(&info, current, &r);
+
+ /* unwind stack */
+ ++level;
+ do {
+ if (unwind_once(&info) < 0 || info.ip == 0)
+ return 0;
+ if (!__kernel_text_address(info.ip)) {
+ return 0;
+ }
+ } while (info.ip && level--);
+
+ return info.ip;
+}
+
Can you show an objdump of this function once it is compiled? I suspect
the stack pointer initialization here is not reliable.
Ideally unwind_frame_init is called with the frame address in gr[30].
With a big struct like pt_regs on the stack, the sp initialization might
be quite far from the actual frame address.
The unwind_once() code uses like heuristics to try to recover from
inaccurate stack pointers (by aligning and stepping the frame 64 bytes
at a time) but that is really a brute force guess.
I realize I used a similar construct in traps.c, but even there I think
it doesn't work reliably.
Maybe somebody else on the list (Dave? :) can suggest a better way to do
this.
randolph
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