[PATCH 6/9] MIPS: Send SIGILL for linked branches in `__compute_return_epc_for_insn'

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Fix commit 319824eabc3f ("MIPS: kernel: branch: Do not emulate the 
branch likelies on MIPS R6") and also send SIGILL rather than returning 
-SIGILL for BLTZAL, BLTZALL, BGEZAL and BGEZALL instruction encodings no 
longer supported in R6, except where emulated.  Returning -SIGILL is 
never correct as the API defines this function's result upon error to be 
-EFAULT and a signal actually issued.

Cc: stable@xxxxxxxxxxxxxxx # 3.19+
Fixes: 319824eabc3f ("MIPS: kernel: branch: Do not emulate the branch likelies on MIPS R6")
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxx>
---
linux-mips-epc-for-insn-sigill-r2r6.diff
Index: linux-sfr-test/arch/mips/kernel/branch.c
===================================================================
--- linux-sfr-test.orig/arch/mips/kernel/branch.c	2017-06-01 06:33:27.149519000 +0100
+++ linux-sfr-test/arch/mips/kernel/branch.c	2017-06-01 06:33:32.663567000 +0100
@@ -473,10 +473,8 @@ int __compute_return_epc_for_insn(struct
 		case bltzal_op:
 		case bltzall_op:
 			if (NO_R6EMU && (insn.i_format.rs ||
-			    insn.i_format.rt == bltzall_op)) {
-				ret = -SIGILL;
-				break;
-			}
+			    insn.i_format.rt == bltzall_op))
+				goto sigill_r2r6;
 			regs->regs[31] = epc + 8;
 			/*
 			 * OK we are here either because we hit a NAL
@@ -507,10 +505,8 @@ int __compute_return_epc_for_insn(struct
 		case bgezal_op:
 		case bgezall_op:
 			if (NO_R6EMU && (insn.i_format.rs ||
-			    insn.i_format.rt == bgezall_op)) {
-				ret = -SIGILL;
-				break;
-			}
+			    insn.i_format.rt == bgezall_op))
+				goto sigill_r2r6;
 			regs->regs[31] = epc + 8;
 			/*
 			 * OK we are here either because we hit a BAL




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