[llvm-commits] [compiler-rt] r159294 - in /compiler-rt/trunk/lib: sanitizer_common/sanitizer_internal_defs.h tsan/rtl/tsan_defs.h tsan/rtl/tsan_flags.cc tsan/rtl/tsan_interceptors.cc tsan/rtl/tsan_md5.cc tsan/rtl/tsan_rtl_report.cc tsan/rtl/tsan_

[Dmitry Vyukov]

On Thu, Jun 28, 2012 at 1:32 AM, Chandler Carruth <chandlerc at google.com>wrote:

> On Wed, Jun 27, 2012 at 2:16 PM, Dmitry Vyukov <dvyukov at google.com> wrote:
>
>> On Thu, Jun 28, 2012 at 1:07 AM, Chandler Carruth <chandlerc at google.com>wrote:
>>
>>> I suspect you'll need to work still harder than this... =[
>>
>>
>> I know :)
>> Now I need to understand how exactly it is broken.
>>
>
> Hmm, I may also need to better understand what you're attempting to
> achieve with this patch (based on Timur's comment).
>
> You define memset, memcpy, etc in a header file -- what callers use them?
> Most callers moved to 'internal_foo' versions.
>
> To answer Timur's question -- yes its ok, but it's hard to control which
> (instrumented or not-instrumented) gets used if they are inserted by LLVM,
> and thus have the normal names. It occurs to me that my post-process
> name-mangling tool would solve this problem as well...
>
>
>>
>> You'll need to compile with -fno-builtins in order to prevent LLVM's
>>> optimizer from recognizing your code as equivalent to 'memset' or 'memcpy',
>>> and replacing it with a call to those functions. =/
>>>
>>
>> I believe we are compiling with -fno-builtin.
>> You mentioned that I also need -ffreestanding:
>>
>
> Yea, -ffreestanding may be better. It is a superset of -fno-builtin
>
>
>>  "Yes, there are attributes which can be attached to the
>> non-instrumented memcpy function, provided by the runtime and selected due
>> to -ffreestanding, which will force inlining. __attribute__((always_inline)),
>> __attribute__((flatten))"
>>
>> Why do I need it?
>>
>
> Need which?
>
> You need '-ffreestanding' so that your source code can implement 'memset'
> itself, and that implementation will be used rather than assuming that at
> some point 'libc' will get linked in and we can call *its* memset. This is
> necessary even if your function isn't named 'memset' but something eles.
>
> The __attribute__((always_inline)) is needed if you want to force this
> function to be inlined into its callers. I don't recall off hand why this
> was important?
>


I need to prevent compiler from inserting memxxx() calls into random places
of the runtime. At first glance the patch achieves the goal.
always_inline is required to eliminate calls.
I do not fully understand why  -fno-builtins/-ffreestanding are required.
The idea is that the compiler leaves no calls to memxxx (everything is
inlined).
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