[RFC] Using function clones for Pointer Bounds Checker

[Ilya Enkovich]

2014-05-14 19:09 GMT+04:00 H.J. Lu <hjl.tools@gmail.com>:
> On Wed, May 14, 2014 at 1:18 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>> 2014-05-13 23:21 GMT+04:00 Jeff Law <law@redhat.com>:
>>> 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?

Ilya

>
> --
> H.J.