powerpc/sstep: Fix incorrect return from analyze_instr()

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

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index f859cbb..e96cff8 100644 (file)
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1445,6 +1445,11 @@ 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;
 
@@ -1472,7 +1477,7 @@ 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 */