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std::mt19937 with ARM Compiler 6 uses sys_open and breaks retarget.c

Roman Khazanskii

I'm using Keil V5.30.0.0 and ArmClang.exe V6.14.

When I tried using std::mt19937, like so:

#include <random>

std::mt19937 mt;
std::uniform_int_distribution< uint32_t > dist(0);

auto a = dist( mt );

I got linker errors:

.\obj\rcu.axf: Error: L6200E: Symbol __stdin multiply defined (by stdio_streams.o and retarget.o).
.\obj\rcu.axf: Error: L6200E: Symbol __stdout multiply defined (by stdio_streams.o and retarget.o).
.\obj\rcu.axf: Error: L6200E: Symbol __stderr multiply defined (by stdio_streams.o and retarget.o).

I'm using more or less classical retarget.c, tuned for armclang.

I tried to remove those definitions from retarget.c and then got error:

.\obj\rcu.axf: Error: L6915E: Library reports error: __use_no_semihosting_swi was requested, but _sys_open was referenced

Then I removed asm(".global __use_no_semihosting_swi\n"); and my firmware hit BKPT before main, in call to _sys_open.

Why is this happening? mt19937 and uniform_int_distribution by themselves should not use any IO, should they? 

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