[PATCH 0/3] MIPS: Get ready for non-executable stack.

[David Daney]

From: David Daney <david.daney@xxxxxxxxxx>

Currently the MIPS FPU emulator uses eXecute Out of Line (XOL) on the
stack to handle instructions in the delay slots of FPU branches.
Because of this MIPS cannot have a non-executable stack.

A previous patch set from Leonid Yegoshin attempts to address the
problem by moving the XOL location to a thread private mapping of a
dedicated page.

I present here an alternative: Add an instruction set emulator and use
it to execute the FPU delay slot instructions.  The benefit of this
approach is that we don't have to allocate a page per user-space
thread for XOL, and we keep the TLB handling code slightly simpler as
a result.

Currently this is a proof of concept, as it doesn't yet handle MIPS64
nor microMIPS instructions.  But it is sufficient to run the entire
Debian distribution on a FPU-less CPU.

Comments welcome.

David Daney (3):
  MIPS: Add FPU emulator counter for non-FPU instructions emulated.
  MIPS: Add full ISA emulator.
  MIPS: Use full instruction emulation for FPU emulator delay slot
    emulation.

 arch/mips/include/asm/fpu_emulator.h |   1 +
 arch/mips/kernel/Makefile            |   3 +-
 arch/mips/kernel/insn-emul.c         | 815 +++++++++++++++++++++++++++++++++++
 arch/mips/math-emu/cp1emu.c          |  13 +-
 arch/mips/math-emu/me-debugfs.c      |   1 +
 5 files changed, 830 insertions(+), 3 deletions(-)
 create mode 100644 arch/mips/kernel/insn-emul.c

-- 
1.7.11.7

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