re-entrant stdio example for multithreaded semihosting

I doubt the semihosting works in multi thread scenario. To support mutli thread, one has to implement target syscalls in compliance with rules as documented in one of the newlib.h.
But I know little about ChibiOs and its multi thread problem with semihosting, so may be talking something wrong.

Whereas in fact it's easy to debug newlib/libgloss in single thread environment. You can rebuild newlib with debug info (even with -O0), install it in toolchain directory and replace old ones; link against it; then debug it along with applications.

Hoping this can help. And we do want to help on this issue to explore multi-thread support in semihosting.
Thanks.

I have been having trouble building with ./build-toolchain --debug (see https://answers.launchpad.net/gcc-arm-embedded/+question/229127), though I think we are almost there.

Regarding ChibiOS/RT, I have a few examples that appear to work in single thread mode, but not the reentrant newlib or newlib-nano printf()'s (even though it is still single thread mode).

ChibiOS/RT may be able to handle multi-threaded semihosting in a similar way that it handles it's SDx class serial driver, which is a locking queue. Right now I have extended the BaseChannel class to some barebones semihosting functions, such as SYS_WRITE 0x05 that looks like this (without the wrapper code for BaseChannel):

static size_t shwrite(BaseChannel *stream, const char *ptr, size_t size)
{
  (void)stream;
  uint32_t retval = -1;
  static uint32_t args[3]; // 3 word block
  args[0] = 1; // file handle, i.e. from SYS_OPEN
  args[1] = (uint32_t)ptr; // ptr to write buffer
  args[2] = size; // number of bytes to be written
  // Extended asm
  // http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#s5
  // asm( asm template : output operands : input ops : clobbered registers );
  asm("mov r0, #0x05\n" // r0 <= SYS_WRITE
      "mov r1, %1\n" // r1 <= ptr_to_3_word_block(args)
      "bkpt 0x00ab" // ARM semihosting breakpoint call
      : "=r" (retval) // out to register.
      : "r" (args) // in on register.
      : "r0", "r1" ); // clobbered registers
  return retval; // 0 if successful or # bytes not written
}

int main(void) {
  uint8_t str1[] = "Raw DeadSemiBeef!\n";
  halInit();
  chSysInit();

  shwrites(chp, str1, NULL);
  return 0;
}