[Qemu-devel] Re: [RFC][PATCH] x86: CS limit checks

[Jan Kiszka <jan.kiszka@web.de>]

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Jan Kiszka wrote:
> Fabrice Bellard wrote:
>> Jan Kiszka wrote:
>>> Here is a proposal for adding code segment limit checks to x86. This
>>> patch should not need the -seg-checks switch as its tests are mostly
>>> performed during translation time. Moreover, I tried to confine the
>>> small additional overhead in the TB lookup procedure to x86 and Sparc.
>>>
>>> Note that this patch depends on my debugging series, namely [1], as that
>>> one reduces the x86-specific code passages for TB generation. Also note
>>> that this patch is early and only lightly tested so far, not yet
>>> intended for inclusion, but definitely for commenting on!
>> Using more than 32 bits for cs_limit (and cs_base) in the TB is
>> wasteful, so I strongly suggest to use a uint32_t type. In that case,
>> cs_limit must be explicitely ignored in 64 bit code.
>>
>> @@ -172,6 +173,8 @@ static inline TranslationBlock *tb_find_
>>      flags = env->hflags;
>>      flags |= (env->eflags & (IOPL_MASK | TF_MASK | VM_MASK));
>>      cs_base = env->segs[R_CS].base;
>> +    if ((env->hflags & (HF_PE_MASK | HF_CS64_MASK)) == HF_PE_MASK)
>> +        cs_limit = env->segs[R_CS].limit;
>>      pc = cs_base + env->eip;
>>
>> This test should be suppressed for performance reasons.
> 
> Yes, the test should be moved to the translator code. This will also
> allow to reduce the width of cs_base/limit.

cs_base must remain target_ulong - sparc relies on it for storing npc.

Jan


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