[Qemu-devel] [PATCH] add cacheflush in tcg_gen_code_search_pc.

[Qemu-devel] [PATCH] add cacheflush in tcg_gen_code_search_pc.

[qiaochong]

 Without cacheflush,qemu sometimes fail with segment fault on loongson
 cpu,which often happens when linux begin to run init.Because user
 porgram tlb refill,tlbl,tlbs,tlbm exception will often happen,
 cpu_restore_state,tcg_gen_code-pc will be called frequently.

Signed-off-by: qiaochong <qiaochong@loongson.cn>
---
 tcg/tcg.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/tcg/tcg.c b/tcg/tcg.c
index e0a9030..b5e274c 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -2120,7 +2120,12 @@ int tcg_gen_code(TCGContext *s, uint8_t *gen_code_buf)
    Return -1 if not found. */
 int tcg_gen_code_search_pc(TCGContext *s, uint8_t *gen_code_buf, long offset)
 {
-    return tcg_gen_code_common(s, gen_code_buf, offset);
+    int ret;
+    ret = tcg_gen_code_common(s, gen_code_buf, offset);
+    /* flush instruction cache */
+    flush_icache_range((unsigned long)gen_code_buf, 
+                       (unsigned long)s->code_ptr);
+    return ret;
 }
 
 #ifdef CONFIG_PROFILER
-- 
1.7.0.3.dirty

Re: [Qemu-devel] [PATCH] add cacheflush in tcg_gen_code_search_pc.

[Aurelien Jarno]

Hi,

On Mon, Oct 04, 2010 at 05:23:06PM +0800, qiaochong wrote:
>  Without cacheflush,qemu sometimes fail with segment fault on loongson
>  cpu,which often happens when linux begin to run init.Because user
>  porgram tlb refill,tlbl,tlbs,tlbm exception will often happen,
>  cpu_restore_state,tcg_gen_code-pc will be called frequently.

It should not be needed to flush the cache after code retranslation, as
it is not supposed to change the code. The problem you see there is
actually a bug in the code generation that make the code to be
(temporarily) different during the code retranslation.

See http://lists.nongnu.org/archive/html/qemu-devel/2011-01/msg00552.html
and http://lists.nongnu.org/archive/html/qemu-devel/2011-01/msg00553.html
for more details.

Aurelien


> Signed-off-by: qiaochong <qiaochong@loongson.cn>
> ---
>  tcg/tcg.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index e0a9030..b5e274c 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -2120,7 +2120,12 @@ int tcg_gen_code(TCGContext *s, uint8_t *gen_code_buf)
>     Return -1 if not found. */
>  int tcg_gen_code_search_pc(TCGContext *s, uint8_t *gen_code_buf, long offset)
>  {
> -    return tcg_gen_code_common(s, gen_code_buf, offset);
> +    int ret;
> +    ret = tcg_gen_code_common(s, gen_code_buf, offset);
> +    /* flush instruction cache */
> +    flush_icache_range((unsigned long)gen_code_buf, 
> +                       (unsigned long)s->code_ptr);
> +    return ret;
>  }
>  
>  #ifdef CONFIG_PROFILER
> -- 
> 1.7.0.3.dirty
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net