linux-kernel - [PATCH 3/3] MIPS: Use full instruction emulation for FPU emulator delay slot emulation.

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Date:	Wed,  3 Dec 2014 15:44:18 -0800
From:	David Daney <ddaney.cavm@...il.com>
To:	linux-mips@...ux-mips.org, ralf@...ux-mips.org
Cc:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	Zubair.Kakakhel@...tec.com, geert+renesas@...der.be,
	peterz@...radead.org, paul.gortmaker@...driver.com,
	macro@...ux-mips.org, chenhc@...ote.com, cl@...ux.com,
	mingo@...nel.org, richard@....at, zajec5@...il.com,
	james.hogan@...tec.com, keescook@...omium.org, tj@...nel.org,
	alex@...x-smith.me.uk, pbonzini@...hat.com, blogic@...nwrt.org,
	paul.burton@...tec.com, qais.yousef@...tec.com,
	linux-kernel@...r.kernel.org, markos.chandras@...tec.com,
	dengcheng.zhu@...tec.com, manuel.lauss@...il.com,
	lars.persson@...s.com, David Daney <david.daney@...ium.com>
Subject: [PATCH 3/3] MIPS: Use full instruction emulation for FPU emulator delay slot emulation.

From: David Daney <david.daney@...ium.com>

Current delay slot handling does eXecute Out of Line (XOL) on the
stack, which prevents a non-executable stack.  Use the instruction
emulator instead.

Tested by booting 32-bit Debian on OCTEON.  More than 1700
instructions emulated to login to command line.

Signed-off-by: David Daney <david.daney@...ium.com>
---
 arch/mips/math-emu/cp1emu.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index cac529a..787de7a 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -694,11 +694,12 @@ do {									\
  * Emulate the single floating point instruction pointed at by EPC.
  * Two instructions if the instruction is in a branch delay slot.
  */
-
+int mips_insn_emul(struct pt_regs *regs, mips_instruction ir, void *__user *fault_addr);
 static int cop1Emulate(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
 		struct mm_decoded_insn dec_insn, void *__user *fault_addr)
 {
 	unsigned long contpc = xcp->cp0_epc + dec_insn.pc_inc;
+	unsigned long origpc = xcp->cp0_epc;
 	unsigned int cond, cbit;
 	mips_instruction ir;
 	int likely, pc_inc;
@@ -1038,7 +1039,15 @@ emul:
 				 * Single step the non-cp1
 				 * instruction in the dslot
 				 */
-				return mips_dsemul(xcp, ir, contpc);
+				sig = mips_insn_emul(xcp, ir, fault_addr);
+				if (sig == 0) {
+					xcp->cp0_epc = contpc;
+					MIPS_FPU_EMU_INC_STATS(insn_emul);
+				} else {
+					xcp->cp0_epc = origpc;
+					pr_err("mips_insn_emul: %08x ->%d\n", (unsigned)ir, sig);
+				}
+				return sig;
 			} else if (likely) {	/* branch not taken */
 					/*
 					 * branch likely nullifies
-- 
1.7.11.7

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