[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_

[Chandler Carruth]

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?
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