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  1. 12 5月, 2011 2 次提交
    • A
      ARM: 6892/1: handle ptrace requests to change PC during interrupted system calls · 2af68df0
      由 Arnd Bergmann 提交于 
      GDB's interrupt.exp test cases currenly fail on ARM.  The problem is how do_signal
handled restarting interrupted system calls:

The entry.S assembler code determines that we come from a system call; and that
information is passed as "syscall" parameter to do_signal.  That routine then
calls get_signal_to_deliver [*] and if a signal is to be delivered, calls into
handle_signal.  If a system call is to be restarted either after the signal
handler returns, or if no handler is to be called in the first place, the PC
is updated after the get_signal_to_deliver call, either in handle_signal (if
we have a handler) or at the end of do_signal (otherwise).

Now the problem is that during [*], the call to get_signal_to_deliver, a ptrace
intercept may happen.  During this intercept, the debugger may change registers,
including the PC.  This is done by GDB if it wants to execute an "inferior call",
i.e. the execution of some code in the debugged program triggered by GDB.

To this purpose, GDB will save all registers, allocate a stack frame, set up
PC and arguments as appropriate for the call, and point the link register to
a dummy breakpoint instruction.  Once the process is restarted, it will execute
the call and then trap back to the debugger, at which point GDB will restore
all registers and continue original execution.

This generally works fine.  However, now consider what happens when GDB attempts
to do exactly that while the process was interrupted during execution of a to-be-
restarted system call:  do_signal is called with the syscall flag set; it calls
get_signal_to_deliver, at which point the debugger takes over and changes the PC
to point to a completely different place.  Now get_signal_to_deliver returns
without a signal to deliver; but now do_signal decides it should be restarting
a system call, and decrements the PC by 2 or 4 -- so it now points to 2 or 4
bytes before the function GDB wants to call -- which leads to a subsequent crash.

To fix this problem, two things need to be supported:
- do_signal must be able to recognize that get_signal_to_deliver changed the PC
  to a different location, and skip the restart-syscall sequence
- once the debugger has restored all registers at the end of the inferior call
  sequence, do_signal must recognize that *now* it needs to restart the pending
  system call, even though it was now entered from a breakpoint instead of an
  actual svc instruction

This set of issues is solved on other platforms, usually by one of two
mechanisms:

- The status information "do_signal is handling a system call that may need
  restarting" is itself carried in some register that can be accessed via
  ptrace.  This is e.g. on Intel the "orig_eax" register; on Sparc the kernel
  defines a magic extra bit in the flags register for this purpose.
  This allows GDB to manage that state: reset it when doing an inferior call,
  and restore it after the call is finished.

- On s390, do_signal transparently handles this problem without requiring
  GDB interaction, by performing system call restarting in the following
  way: first, adjust the PC as necessary for restarting the call.  Then,
  call get_signal_to_deliver; and finally just continue execution at the
  PC.  This way, if GDB does not change the PC, everything is as before.
  If GDB *does* change the PC, execution will simply continue there --
  and once GDB restores the PC it saved at that point, it will automatically
  point to the *restarted* system call.  (There is the minor twist how to
  handle system calls that do *not* need restarting -- do_signal will undo
  the PC change in this case, after get_signal_to_deliver has returned, and
  only if ptrace did not change the PC during that call.)

Because there does not appear to be any obvious register to carry the
syscall-restart information on ARM, we'd either have to introduce a new
artificial ptrace register just for that purpose, or else handle the issue
transparently like on s390.  The patch below implements the second option;
using this patch makes the interrupt.exp test cases pass on ARM, with no
regression in the GDB test suite otherwise.

Cc: patches@linaro.org
Signed-off-by: NUlrich Weigand <ulrich.weigand@linaro.org>
Signed-off-by: NArnd Bergmann <arnd.bergmann@linaro.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      2af68df0
    • W
      ARM: 6890/1: memmap: only free allocated memmap entries when using SPARSEMEM · 9af386c8
      由 Will Deacon 提交于 
      The SPARSEMEM code allocates memmap entries only for sections which are
present (i.e. those which contain some valid memory). The membank checks
in free_unused_memmap do not take this into account and can incorrectly
attempt to free memory which is not allocated, resulting in a BUG() in
the bootmem code.

However, if memory is configured as follows:

    |<----section---->|<----hole---->|<----section---->|
    +--------+--------+--------------+--------+--------+
    | bank 0 | unused |              | bank 1 | unused |
    +--------+--------+--------------+--------+--------+

where a bank only occupies part of a section, the memmap allocated for
the remainder of the section *can* be freed.

This patch modifies the checks in free_unused_memmap so that only valid
memmap entries are considered for removal.
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      9af386c8
  3. 07 5月, 2011 5 次提交
  5. 06 5月, 2011 2 次提交
    • R
      ARM: RiscPC: acornfb: fix section mismatches · 52fe1163
      由 Russell King 提交于 
      WARNING: drivers/video/built-in.o(.devinit.text+0x38): Section mismatch in reference from the function acornfb_probe() to the function .init.text:acornfb_setup()
The function __devinit acornfb_probe() references
a function __init acornfb_setup().
If acornfb_setup is only used by acornfb_probe then
annotate acornfb_setup with a matching annotation.

WARNING: drivers/video/built-in.o(.devinit.text+0x3c): Section mismatch in reference from the function acornfb_probe() to the function .init.text:acornfb_init_fbinfo()
The function __devinit acornfb_probe() references
a function __init acornfb_init_fbinfo().
If acornfb_init_fbinfo is only used by acornfb_probe then
annotate acornfb_init_fbinfo with a matching annotation.

WARNING: drivers/video/built-in.o(.devinit.text+0x4c0): Section mismatch in reference from the function acornfb_probe() to the (unknown reference) .init.data:(unknown)
The function __devinit acornfb_probe() references
a (unknown reference) __initdata (unknown).
If (unknown) is only used by acornfb_probe then
annotate (unknown) with a matching annotation.

WARNING: drivers/video/built-in.o(.devinit.text+0x4c8): Section mismatch in reference from the function acornfb_probe() to the (unknown reference) .init.data:(unknown)
The function __devinit acornfb_probe() references
a (unknown reference) __initdata (unknown).
If (unknown) is only used by acornfb_probe then
annotate (unknown) with a matching annotation.

WARNING: drivers/video/built-in.o(.devinit.text+0x4cc): Section mismatch in reference from the function acornfb_probe() to the (unknown reference) .init.data:(unknown)
The function __devinit acornfb_probe() references
a (unknown reference) __initdata (unknown).
If (unknown) is only used by acornfb_probe then
annotate (unknown) with a matching annotation.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      52fe1163
    • R
      ARM: RiscPC: etherh: fix section mismatches · 56f3aeb2
      由 Russell King 提交于 
      WARNING: drivers/net/arm/built-in.o(.data+0x0): Section mismatch in reference from the variable etherh_driver to the function .init.text:etherh_probe()
The variable etherh_driver references
the function __init etherh_probe()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
      56f3aeb2
  7. 05 5月, 2011 8 次提交
  9. 04 5月, 2011 17 次提交
  11. 03 5月, 2011 6 次提交