x86: fix 32-bit FRAME_POINTER chasing code

x86: fix 32-bit FRAME_POINTER chasing code

The current x86 32 bit FRAME_POINTER chasing code has a nasty bug in
that the EBP tracer doesn't actually update the value of EBP it is
tracing, so that the code doesn't actually switch to the irq stack
properly.

The result is a truncated backtrace:

 WARNING: at timeroops.c:8 kerneloops_regression_test() (Not tainted)
 Pid: 0, comm: swapper Not tainted 2.6.24-0.77.rc4.git4.fc9 #1
  [<c040649a>] show_trace_log_lvl+0x1a/0x2f
  [<c0406d41>] show_trace+0x12/0x14
  [<c0407061>] dump_stack+0x6c/0x72
  [<e0258049>] kerneloops_regression_test+0x44/0x46 [timeroops]
  [<c04371ac>] run_timer_softirq+0x127/0x18f
  [<c0434685>] __do_softirq+0x78/0xff
  [<c0407759>] do_softirq+0x74/0xf7
  =======================

This patch fixes the code to update EBP properly, and to check the EIP
before printing (as the non-framepointer backtracer does) so that
the same test backtrace now looks like this:

 WARNING: at timeroops.c:8 kerneloops_regression_test()
 Pid: 0, comm: swapper Not tainted 2.6.24-rc7 #4
  [<c0405d17>] show_trace_log_lvl+0x1a/0x2f
  [<c0406681>] show_trace+0x12/0x14
  [<c0406ef2>] dump_stack+0x6a/0x70
  [<e01f6040>] kerneloops_regression_test+0x3b/0x3d [timeroops]
  [<c0426f07>] run_timer_softirq+0x11b/0x17c
  [<c04243ac>] __do_softirq+0x42/0x94
  [<c040704c>] do_softirq+0x50/0xb6
  [<c04242a9>] irq_exit+0x37/0x67
  [<c040714c>] do_IRQ+0x9a/0xaf
  [<c04057da>] common_interrupt+0x2e/0x34
  [<c05807fe>] cpuidle_idle_call+0x52/0x78
  [<c04034f3>] cpu_idle+0x46/0x60
  [<c05fbbd3>] rest_init+0x43/0x45
  [<c070aa3d>] start_kernel+0x279/0x27f
  =======================

This shows that the backtrace goes all the way down to user context now.
This bug was found during the port to 64 bit of the frame pointer backtracer.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>