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gcc: Provide _sbrk implementation compatible with RTX #48

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Merged
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Sep 4, 2013
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gcc: Provide _sbrk implementation compatible with RTX #48

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27 changes: 27 additions & 0 deletions libraries/mbed/common/retarget.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -425,3 +425,30 @@ extern "C" void __iar_argc_argv() {
mbed_main();
}
#endif

// Provide implementation of _sbrk (low-level dynamic memory allocation
// routine) for GCC_ARM which compares new heap pointer with MSP instead of
// SP. This make it compatible with RTX RTOS thread stacks.
#if defined(TOOLCHAIN_GCC_ARM)
// Linker defined symbol used by _sbrk to indicate where heap should start.
extern "C" int __end__;

// Turn off the errno macro and use actual global variable instead.
#undef errno
extern "C" int errno;

// Dynamic memory allocation related syscall.
extern "C" caddr_t _sbrk(int incr) {
static unsigned char* heap = (unsigned char*)&__end__;
unsigned char* prev_heap = heap;
unsigned char* new_heap = heap + incr;
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It might be a good idea to align the new_heap pointer, as it happens for example here:

https://github.com/mbedmicro/mbed/blob/master/libraries/mbed/targets/cmsis/TARGET_NXP/TARGET_LPC176X/TOOLCHAIN_GCC_CS/sys.cpp

Not sure if this is a hard requirement, but it seems to be a bit safer.


if (new_heap >= (unsigned char*)__get_MSP()) {
errno = ENOMEM;
return (caddr_t)-1;
}

heap = new_heap;
return (caddr_t) prev_heap;
}
#endif