Re: [Qemu-devel] [PATCH 07/11] cris: avoid write only variables

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Thu, Oct 07, 2010 at 12:08:05PM +0200, Markus Armbruster wrote:
> Blue Swirl <blauwirbel@gmail.com> writes:
> 
> > Compiling with GCC 4.6.0 20100925 produced warnings:
> > /src/qemu/target-cris/op_helper.c: In function 'helper_movl_sreg_reg':
> > /src/qemu/target-cris/op_helper.c:145:8: error: variable 'tlb_v' set
> > but not used [-Werror=unused-but-set-variable]
> > In file included from /src/qemu/target-cris/translate.c:3154:0:
> > /src/qemu/target-cris/translate_v10.c: In function 'dec10_prep_move_m':
> > /src/qemu/target-cris/translate_v10.c:111:22: error: variable 'rd' set
> > but not used [-Werror=unused-but-set-variable]
> >
> > Fix by making the variable declarations and their uses also conditional
> > to debug definition, delete rd.
> >
> > Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
> > ---
> >  target-cris/op_helper.c     |    6 ++++++
> >  target-cris/translate_v10.c |    5 ++---
> >  2 files changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/target-cris/op_helper.c b/target-cris/op_helper.c
> > index a60da94..28c79b1 100644
> > --- a/target-cris/op_helper.c
> > +++ b/target-cris/op_helper.c
> > @@ -142,7 +142,9 @@ void helper_movl_sreg_reg (uint32_t sreg, uint32_t reg)
> >  			uint32_t idx;
> >  			uint32_t lo, hi;
> >  			uint32_t vaddr;
> > +#ifdef CRIS_OP_HELPER_DEBUG
> >  			int tlb_v;
> > +#endif
> >
> >  			idx = set = env->sregs[SFR_RW_MM_TLB_SEL];
> >  			set >>= 4;
> > @@ -157,13 +159,17 @@ void helper_movl_sreg_reg (uint32_t sreg, uint32_t reg)
> >  			vaddr = EXTRACT_FIELD(env->tlbsets[srs-1][set][idx].hi,
> >  					      13, 31);
> >  			vaddr <<= TARGET_PAGE_BITS;
> > +#ifdef CRIS_OP_HELPER_DEBUG
> >  			tlb_v = EXTRACT_FIELD(env->tlbsets[srs-1][set][idx].lo,
> >  					    3, 3);
> > +#endif
> >  			env->tlbsets[srs - 1][set][idx].lo = lo;
> >  			env->tlbsets[srs - 1][set][idx].hi = hi;
> >
> > +#ifdef CRIS_OP_HELPER_DEBUG
> >  			D_LOG("tlb flush vaddr=%x v=%d pc=%x\n",
> >  				  vaddr, tlb_v, env->pc);
> > +#endif
> >  			tlb_flush_page(env, vaddr);
> >  		}
> >  	}
> 
> Could we eliminate the bothersome variable instead?
> 
> diff --git a/target-cris/op_helper.c b/target-cris/op_helper.c
> index a60da94..94e3e27 100644
> --- a/target-cris/op_helper.c
> +++ b/target-cris/op_helper.c
> @@ -142,7 +142,6 @@ void helper_movl_sreg_reg (uint32_t sreg, uint32_t reg)
>  			uint32_t idx;
>  			uint32_t lo, hi;
>  			uint32_t vaddr;
> -			int tlb_v;
>  
>  			idx = set = env->sregs[SFR_RW_MM_TLB_SEL];
>  			set >>= 4;
> @@ -157,13 +156,14 @@ void helper_movl_sreg_reg (uint32_t sreg, uint32_t reg)
>  			vaddr = EXTRACT_FIELD(env->tlbsets[srs-1][set][idx].hi,
>  					      13, 31);
>  			vaddr <<= TARGET_PAGE_BITS;
> -			tlb_v = EXTRACT_FIELD(env->tlbsets[srs-1][set][idx].lo,
> +			D_LOG("tlb flush vaddr=%x v=%d pc=%x\n", 
> +                              vaddr,
> +                              EXTRACT_FIELD(env->tlbsets[srs-1][set][idx].lo,
>  					    3, 3);
> +                              env->pc);
>  			env->tlbsets[srs - 1][set][idx].lo = lo;
>  			env->tlbsets[srs - 1][set][idx].hi = hi;
>  
> -			D_LOG("tlb flush vaddr=%x v=%d pc=%x\n", 
> -				  vaddr, tlb_v, env->pc);
>  			tlb_flush_page(env, vaddr);
>  		}
>  	}

Hi,

Sorry for the late answer.

Markus, I agree that removing tlb_v would have been better than ifdefs,
but i think that the intent I originally had in mind was that there should
not be a need to flush the entry from the QEMU TLB if the old guest
entry was not valid. 


The following patch works on my side:

diff --git a/target-cris/op_helper.c b/target-cris/op_helper.c
index a60da94..be9eb06 100644
--- a/target-cris/op_helper.c
+++ b/target-cris/op_helper.c
@@ -164,7 +164,9 @@ void helper_movl_sreg_reg (uint32_t sreg, uint32_t reg)
 
 			D_LOG("tlb flush vaddr=%x v=%d pc=%x\n", 
 				  vaddr, tlb_v, env->pc);
-			tlb_flush_page(env, vaddr);
+			if (tlb_v) {
+				tlb_flush_page(env, vaddr);
+			}
 		}
 	}
 #endif


The target-cris/translate_v10.c hunk looks good.

Blue, can you incorporate the tlb_v change in your patch set?
Or if you prefer, I can commit that part on my side.

Cheers