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- m68knommu: fix user a5 register being overwritten
- On no-MMU systems the application a5 register can be overwitten with the
- address of the process data segment when processing application signals.
- For flat format applications compiled with full absolute relocation this
- effectively corrupts the a5 register on signal processing - and this very
- quickly leads to process crash and often takes out the whole system with
- a panic as well.
- This has no effect on flat format applications compiled with the more
- common PIC methods (such as -msep-data). These format applications reserve
- a5 for the pointer to the data segment anyway - so it doesn't change it.
- A long time ago the a5 register was used in the code packed into the user
- stack to enable signal return processing. And so it had to be restored on
- end of signal cleanup processing back to the original a5 user value. This
- was historically done by saving away a5 in the sigcontext structure. At
- some point (a long time back it seems) the a5 restore process was changed
- and it was hard coded to put the user data segment address directly into a5.
- Which is ok for the common PIC compiled application case, but breaks the
- full relocation application code.
- We no longer use this type of signal handling mechanism and so we don't
- need to do anything special to save and restore a5 at all now. So remove the
- code that hard codes a5 to the address of the user data segment.
- Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
- ---
- arch/m68k/kernel/signal.c | 1 -
- 1 file changed, 1 deletion(-)
- diff --git a/arch/m68k/kernel/signal.c b/arch/m68k/kernel/signal.c
- index 2dcee3a..9202f82 100644
- --- a/arch/m68k/kernel/signal.c
- +++ b/arch/m68k/kernel/signal.c
- @@ -213,7 +213,6 @@ static inline int frame_extra_sizes(int f)
-
- static inline void adjustformat(struct pt_regs *regs)
- {
- - ((struct switch_stack *)regs - 1)->a5 = current->mm->start_data;
- /*
- * set format byte to make stack appear modulo 4, which it will
- * be when doing the rte
- --
- 1.9.1
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