From b0490a04e736356e427e227902b17f9927a56caf Mon Sep 17 00:00:00 2001 From: Sandipan Das Date: Tue, 10 Oct 2017 12:15:30 +0530 Subject: [PATCH] powerpc/lib/sstep: Fix count leading zeros instructions According to the GCC documentation, the behaviour of __builtin_clz() and __builtin_clzl() is undefined if the value of the input argument is zero. Without handling this special case, these builtins have been used for emulating the following instructions: * Count Leading Zeros Word (cntlzw[.]) * Count Leading Zeros Doubleword (cntlzd[.]) This fixes the emulated behaviour of these instructions by adding an additional check for this special case. Fixes: 3cdfcbfd32b9d ("powerpc: Change analyse_instr so it doesn't modify *regs") Signed-off-by: Sandipan Das Reviewed-by: Naveen N. Rao Signed-off-by: Michael Ellerman --- arch/powerpc/lib/sstep.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c index 5e8418c28bd8..f208f560aecd 100644 --- a/arch/powerpc/lib/sstep.c +++ b/arch/powerpc/lib/sstep.c @@ -1684,11 +1684,13 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs, * Logical instructions */ case 26: /* cntlzw */ - op->val = __builtin_clz((unsigned int) regs->gpr[rd]); + val = (unsigned int) regs->gpr[rd]; + op->val = ( val ? __builtin_clz(val) : 32 ); goto logical_done; #ifdef __powerpc64__ case 58: /* cntlzd */ - op->val = __builtin_clzl(regs->gpr[rd]); + val = regs->gpr[rd]; + op->val = ( val ? __builtin_clzl(val) : 64 ); goto logical_done; #endif case 28: /* and */ -- 2.20.1