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

[Blue Swirl]

Thanks, applied.

On Wed, Jul 6, 2011 at 2:15 PM, Peter Maydell <address@hidden> wrote:
> 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
>
>