On Thu, May 15, 2014 at 1:07 PM, Ilya Enkovich <[email protected]> wrote:
> 2014-05-14 19:09 GMT+04:00 H.J. Lu <[email protected]>:
>> On Wed, May 14, 2014 at 1:18 AM, Ilya Enkovich <[email protected]>
>> wrote:
>>> 2014-05-13 23:21 GMT+04:00 Jeff Law <[email protected]>:
>>>> On 05/13/14 02:38, Ilya Enkovich wrote:
>>>>>>>
>>>>>>> propagate constant bounds value and remove checks in called function).
>>>>>>
>>>>>>
>>>>>> So from a linking standpoint, presumably you have to mangle the
>>>>>> instrumented
>>>>>> caller/callee in some manner. Right? Or are you dynamically dispatching
>>>>>> somehow?
>>>>>
>>>>>
>>>>> Originally the idea was o have instrumented clone to have the same
>>>>> assembler name as the original function. Since instrumented code is
>>>>> fully compatible with not instrumented code, we always emit only one
>>>>> version. Usage of the same assembler name allows instrumented and not
>>>>> instrumented calls to look similar in assembler. It worked fine until
>>>>> I tried it with LTO where assembler name is used as a unique
>>>>> identifier. With linker resolutions files it became even more harder
>>>>> to use such approach. To resolve these issues I started to use new
>>>>> assembler name with postfix, but linked with the original name using
>>>>> IDENTIFIER_TRANSPARENT_ALIAS. It gives different assembler names for
>>>>> clones and originals during compilation, but both clone and original
>>>>> functions have similar name in output assembler.
>>>>
>>>> OK. So if I read that correctly, it implies that the existence of bounds
>>>> information does not change the signature of the callee. This is
>>>> obviously
>>>> important for C++.
>>>>
>>>> Sounds like I need to sit down with the branch and see how this works in
>>>> the
>>>> new scheme.
>>>
>>> Both mpx branch and Wiki
>>> (http://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler)
>>> page are up-to-date now and may be tried out either in NOP mode or
>>> with simulator. Let me know if you have any troubles with using it.
>>>
>>
>> I built it. But "-fcheck-pointer-bounds -mmpx" doesn't generate
>> MPX enabled executable which runs on both MPX-enabled and
>> non MPX-enabled hardwares. I didn't see any MPX run-time library.
>
> Just checked out the branch and checked generated code.
>
> #cat test.c
> int
> test (int *p, int i)
> {
> return p[i];
> }
> #gcc -fcheck-pointer-bounds -mmpx test.c -S -O2
> #cat test.s
> .file "test.c"
> .section .text.unlikely,"ax",@progbits
> .LCOLDB0:
> .text
> .LHOTB0:
> .p2align 4,,15
> .globl test
> .type test, @function
> test:
> .LFB1:
> .cfi_startproc
> movslq %esi, %rsi
> leaq (%rdi,%rsi,4), %rax
> bndcl (%rax), %bnd0
> bndcu 3(%rax), %bnd0
> movl (%rax), %eax
> bnd ret
> .cfi_endproc
> ...
>
> Checks are here. What do you see in your test?
Wow, that's quite an overhead compared to the non-instrumented variant
movslq %esi, %rsi
movl (%rdi,%rsi,4), %eax
ret
I thought bounds-checking was done with some clever prefixes thus
that
movslq %esi, %rsi
bndmovl (%rdi,%rsi,4), %eax, %bnd0
bnd ret
would be possible (well, replace with valid ISA).
Richard.
> Ilya
>
>>
>> --
>> H.J.
