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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Ananth N Mavinakayanahalli <ananth@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Sandipan Das <sandipan@linux.ibm.com>
Subject: [PATCH 5.10 093/102] powerpc/sstep: Fix incorrect return from analyze_instr()
Date:   Fri,  5 Mar 2021 13:21:52 +0100
Message-Id: <20210305120907.855387479@linuxfoundation.org>
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From: Ananth N Mavinakayanahalli <ananth@linux.ibm.com>

commit 718aae916fa6619c57c348beaedd675835cf1aa1 upstream.

We currently just percolate the return value from analyze_instr()
to the caller of emulate_step(), especially if it is a -1.

For one particular case (opcode = 4) for instructions that aren't
currently emulated, we are returning 'should not be single-stepped'
while we should have returned 0 which says 'did not emulate, may
have to single-step'.

Fixes: 930d6288a26787 ("powerpc: sstep: Add support for maddhd, maddhdu, maddld instructions")
Signed-off-by: Ananth N Mavinakayanahalli <ananth@linux.ibm.com>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/161157999039.64773.14950289716779364766.stgit@thinktux.local
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/powerpc/lib/sstep.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1382,6 +1382,11 @@ int analyse_instr(struct instruction_op
 
 #ifdef __powerpc64__
 	case 4:
+		/*
+		 * There are very many instructions with this primary opcode
+		 * introduced in the ISA as early as v2.03. However, the ones
+		 * we currently emulate were all introduced with ISA 3.0
+		 */
 		if (!cpu_has_feature(CPU_FTR_ARCH_300))
 			goto unknown_opcode;
 
@@ -1409,7 +1414,7 @@ int analyse_instr(struct instruction_op
 		 * There are other instructions from ISA 3.0 with the same
 		 * primary opcode which do not have emulation support yet.
 		 */
-		return -1;
+		goto unknown_opcode;
 #endif
 
 	case 7:		/* mulli */