ARM: Fix undefined instruction exception handling
authorRussell King <rmk+kernel@arm.linux.org.uk>
Mon, 30 Jul 2012 18:42:10 +0000 (19:42 +0100)
committerBen Hutchings <ben@decadent.org.uk>
Thu, 9 Aug 2012 23:25:06 +0000 (00:25 +0100)
commit83358b9b1d3438293794224b14787a806031cf98
tree8319420eeef4ca77d6819441a3b3d93111ad9f72
parent1b48195822f358b7b5e44369cfa34463f0b9e09f
ARM: Fix undefined instruction exception handling

commit 15ac49b65024f55c4371a53214879a9c77c4fbf9 upstream.

While trying to get a v3.5 kernel booted on the cubox, I noticed that
VFP does not work correctly with VFP bounce handling.  This is because
of the confusion over 16-bit vs 32-bit instructions, and where PC is
supposed to point to.

The rule is that FP handlers are entered with regs->ARM_pc pointing at
the _next_ instruction to be executed.  However, if the exception is
not handled, regs->ARM_pc points at the faulting instruction.

This is easy for ARM mode, because we know that the next instruction and
previous instructions are separated by four bytes.  This is not true of
Thumb2 though.

Since all FP instructions are 32-bit in Thumb2, it makes things easy.
We just need to select the appropriate adjustment.  Do this by moving
the adjustment out of do_undefinstr() into the assembly code, as only
the assembly code knows whether it's dealing with a 32-bit or 16-bit
instruction.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
arch/arm/kernel/entry-armv.S
arch/arm/kernel/traps.c
arch/arm/vfp/entry.S
arch/arm/vfp/vfphw.S