powerpc/sstep: Fix incorrect return from analyze_instr()

stable inclusion
from stable-5.10.21
commit 686fa5a0c647721f24721a53e9d78972eb673e02
bugzilla: 50609

--------------------------------

commit 718aae91 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: 930d6288 ("powerpc: sstep: Add support for maddhd, maddhdu, maddld instructions")
Signed-off-by: NAnanth N Mavinakayanahalli <ananth@linux.ibm.com>
Suggested-by: NMichael Ellerman <mpe@ellerman.id.au>
Tested-by: NNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: NSandipan Das <sandipan@linux.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/161157999039.64773.14950289716779364766.stgit@thinktux.localSigned-off-by: NNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/powerpc/lib/sstep.c

@@ -1382,6 +1382,11 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 
 #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 *op, const struct pt_regs *regs,
 		 * 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 */