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Re: [Qemu-devel] [RFC PATCH v4 10/25] i386: do not cross the pages bound
From: |
Pavel Dovgaluk |
Subject: |
Re: [Qemu-devel] [RFC PATCH v4 10/25] i386: do not cross the pages boundaries in replay mode |
Date: |
Fri, 7 Nov 2014 14:39:12 +0300 |
> From: Paolo Bonzini [mailto:address@hidden
> On 07/11/2014 11:32, Pavel Dovgalyuk wrote:
> > This patch denies crossing the boundary of the pages in the replay mode,
> > because it can cause an exception. Do it only when boundary is
> > crossed by the first instruction in the block.
> > If current instruction already crossed the bound - it's ok,
> > because an exception hasn't stopped this code.
> >
> > Signed-off-by: Pavel Dovgalyuk <address@hidden>
> > ---
> > target-i386/cpu.h | 7 +++++++
> > target-i386/translate.c | 14 ++++++++++++++
> > 2 files changed, 21 insertions(+), 0 deletions(-)
> >
> > diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> > index 2968749..bc3f9f5 100644
> > --- a/target-i386/cpu.h
> > +++ b/target-i386/cpu.h
> > @@ -28,6 +28,13 @@
> > #define TARGET_LONG_BITS 32
> > #endif
> >
> > +/* Maximum instruction code size */
> > +#ifdef TARGET_X86_64
> > +#define TARGET_MAX_INSN_SIZE 16
> > +#else
> > +#define TARGET_MAX_INSN_SIZE 16
> > +#endif
> > +
> > /* target supports implicit self modifying code */
> > #define TARGET_HAS_SMC
> > /* support for self modifying code even if the modified instruction is
> > diff --git a/target-i386/translate.c b/target-i386/translate.c
> > index 4d5dfb3..a264908 100644
> > --- a/target-i386/translate.c
> > +++ b/target-i386/translate.c
> > @@ -8035,6 +8035,20 @@ static inline void
> > gen_intermediate_code_internal(X86CPU *cpu,
> > gen_eob(dc);
> > break;
> > }
> > + /* Do not cross the boundary of the pages in icount mode,
> > + it can cause an exception. Do it only when boundary is
> > + crossed by the first instruction in the block.
> > + If current instruction already crossed the bound - it's ok,
> > + because an exception hasn't stopped this code.
> > + */
> > + if (use_icount
> > + && ((pc_ptr & TARGET_PAGE_MASK)
> > + != ((pc_ptr + TARGET_MAX_INSN_SIZE - 1) & TARGET_PAGE_MASK)
> > + || (pc_ptr & ~TARGET_PAGE_MASK) == 0)) {
> > + gen_jmp_im(pc_ptr - dc->cs_base);
> > + gen_eob(dc);
> > + break;
> > + }
> > /* if too long translation, stop generation too */
> > if (tcg_ctx.gen_opc_ptr >= gen_opc_end ||
> > (pc_ptr - pc_start) >= (TARGET_PAGE_SIZE - 32) ||
> >
>
> Why only in icount mode? Does it have a sensible performance problem?
Maybe. This is the same problem, which was discussed here for ARM:
http://lists.gnu.org/archive/html/qemu-devel/2014-10/msg02232.html
But I haven't figured out what I have to do with it.
Pavel Dovgalyuk
- [Qemu-devel] [RFC PATCH v4 07/25] icount: implement icount requesting, (continued)
[Qemu-devel] [RFC PATCH v4 08/25] icount: improve enable/disable ticks, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 09/25] replay: introduce icount event, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 10/25] i386: do not cross the pages boundaries in replay mode, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 11/25] cpu-exec: allow temporary disabling icount, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 12/25] replay: interrupts and exceptions, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 13/25] replay: asynchronous events infrastructure, Pavel Dovgalyuk, 2014/11/07
[Qemu-devel] [RFC PATCH v4 14/25] cpu: replay instructions sequence, Pavel Dovgalyuk, 2014/11/07