Re: [Qemu-devel] [PATCH] exec-all.h: Make MAX_OP_PER_INSTR large enough for target-arm's uses

[Peter Maydell]

Ping?

On 22 June 2011 15:16, Peter Maydell <address@hidden> wrote:
> The target-arm frontend's worst-case TCG ops per instr is 194 (and in
> general many of the "load multiple registers" ARM instructions generate
> more than 100 TCG ops). Raise MAX_OP_PER_INSTR accordingly to avoid
> possible buffer overruns.
>
> Since it doesn't make any sense for the "64 bit guest on 32 bit host"
> case to have a smaller limit than the normal case, we collapse the
> two cases back into each other again.
>
> (This increase costs us about 14K in extra static buffer space and
> 21K of extra margin at the end of a 32MB codegen buffer.)
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> You might recall the patchset which moves the Neon load/store multiple
> instructions to helper functions, and which turns out to slow them
> down rather a lot. This is the other approach, which is just to
> raise the limit so that the existing implementations don't risk
> buffer overruns. The extra memory costs are tiny IMHO.
> (The Neon instructions are the worst offenders but the VFP load/store
> multiple insns also breach the previous limit. I think we should
> consider an implementation of an instruction that's been basically
> the same since VFP support was added to QEMU in 2005 to be an
> acceptable one, and make sure our buffer sizes cope with it :-))
>
>  exec-all.h |    6 +-----
>  1 files changed, 1 insertions(+), 5 deletions(-)
>
> diff --git a/exec-all.h b/exec-all.h
> index 2a13a95..ef5f5b6 100644
> --- a/exec-all.h
> +++ b/exec-all.h
> @@ -43,11 +43,7 @@ typedef ram_addr_t tb_page_addr_t;
>  typedef struct TranslationBlock TranslationBlock;
>
>  /* XXX: make safe guess about sizes */
> -#if (HOST_LONG_BITS == 32) && (TARGET_LONG_BITS == 64)
> -#define MAX_OP_PER_INSTR 128
> -#else
> -#define MAX_OP_PER_INSTR 96
> -#endif
> +#define MAX_OP_PER_INSTR 208
>
>  #if HOST_LONG_BITS == 32
>  #define MAX_OPC_PARAM_PER_ARG 2
> --
> 1.7.1