[cfe-dev] [libc++] Porting libc++ to embedded targets/compilers

[Friedman, Eli via cfe-dev]

On 9/12/2017 2:41 PM, Nagurne, James via cfe-dev wrote:
>
> Hello,
>
> I am a developer in the compiler division (CodeGen) at Texas 
> Instruments. Our compiler targets a variety of embedded targets from 
> DSPs like the C6000 to microcontrollers like the C2000 and MSP430. All 
> of our compilers use a common, modified EDG C++ front end accepting a 
> majority of the C++14 standard in addition to many extensions allowed 
> by both GCC and Clang, such as __has_feature.
>
> We’re investigating using libc++ in addition to our home grown and 
> augmented C (and C++ implementation-specific behavior) library to fill 
> out our C++ support. Having worked on this for a week or so, I’ve 
> cultivated a list of issues whose answers/solutions will help guide me 
> in completing and trying to upstream some/all of this work.
>
> - Atomic builtins (__sync functions) are assumed to exist, and other 
> atomic issues
>
> Our first drop of C++14 will not have support for threads or atomics, 
> since we’re still talking with other teams which support the low-level 
> operations and APIs needed.
>
> The CMakelists.txt file checks for atomic support, warning “Host 
> compiler must support std::atomic”. Is this a major problem that could 
> stop us from being able to use libc++ immediately?
>
> For the __sync functions, we could define template functions to 
> overload and perform the elemental operation without any guarantee of 
> atomicity (I believe all uses are currently ‘int’ operations). Is this 
> alright, assuming we will not be supporting multiple theads?
>

There's a CMake option LIBCXX_ENABLE_THREADS you can use to turn off 
multi-threaded support... but you might still have trouble with 
atomics.  See https://reviews.llvm.org/D35235 .

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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