where is libatomic?

[greengnu]

I'm tying to compile something like this:

Code: Select all

#include <atomic>

static int test()
{
    std::atomic<long long> x;
    return x;
}

int main()
{
    return test();
}

but I get

Code: Select all

c:/users/username/.espressif/tools/xtensa-esp32-elf/esp32-2019r1-8.2.0/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.2.0/../../../../xtensa-esp32-elf/bin/ld.exe: CMakeFiles/cmTC_bfb5d.dir/atomic_check.cpp.obj:(.literal._ZNKSt13__atomic_baseIxEcvxEv[std::__atomic_base<long long>::operator long long() const]+0x8): undefined reference to `__atomic_load_8'

if I try to link with -latomic linker flag this fails too as there is no libatomic in the toolchain. Where is libatomic or how can I make use of std::atomic?

[WiFive]

https://github.com/espressif/esp-idf/issues/3163

[warren]

Have you tried std::atomic<long> x, that is just one "long" (or try int)?

Code: Select all

static int test()
{
    std::atomic<long> x; // long, not long long
    return x;
}

It is likely that the platform does not support an atomic that large.

[greengnu]

yes, using std::atomic<long> x; works - but it means I have to change existing library code. Would be great to have a software implementation of 64bit atomics

[warren]

The ESP is a 32-bit platform after all, so probably doesn't support a 64-bit atomics. You'll need to look at the xtensa instruction set to confirm but I wouldn't be holding my breath.

[greengnu]

but functions like __atomic_load_8 could still be implemented using semaphores - so just because the hardware doesn't support it doesn't mean the functionality gotta be missing from the library