Wrap printf to avoid lots of unnecessary mallocs.

app/Makefile

@@ -119,7 +119,7 @@ LINKFLAGS_eagle.app.v6 = 			\
 	-Wl,@$(LDDIR)/defsym.rom		\
 	-T$(LDDIR)/extrasyms.rom		\
 	-Wl,--no-check-sections 		\
-	-Wl,--wrap=_xtos_set_exception_handler	\
+	-Wl,--wrap=printf			\
 	-Wl,-static 				\
 	$(addprefix -u , $(SELECTED_MODULE_SYMS)) \
 	-u _UserExceptionVectorOverride		\

app/user/wrap_printf.s

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2016 Dius Computing Pty Ltd. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the
+ *   distribution.
+ * - Neither the name of the copyright holders nor the names of
+ *   its contributors may be used to endorse or promote products derived
+ *   from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * @author Johny Mattsson <jmattsson@dius.com.au>
+ */
+
+/* The RTOS SDK provided printf() function has explicit support for dealing
+ * with formatting strings stored in flash (used via the os_printf macro).
+ * For others, that's a very useful optimisation, but for us it's an unwanted
+ * pessimisation as it forces a malloc for each printf. To avoid this we
+ * have a minimal replacement printf() which omits the explicit flash-support
+ * support, and just calls the internal SDK function print() directly.
+ */
+.section ".iram0.text"
+.type __wrap_printf,@function
+.globl __wrap_printf
+.align 4
+.literal_position
+__wrap_printf:
+  addi a1, a1, -32      /* get some stack space                               */
+  s32i a0, a1,  0       /* store a0 at the bottom                             */
+  s32i a2, a1,  8       /* copy the formatting string and first few arguments */
+  s32i a3, a1, 12       /* ...onto the stack in a way that we get a contiguous*/
+  s32i a4, a1, 16       /* ...array of all arguments to printf, with the      */
+  s32i a5, a1, 20       /* ...formatting string in the first array slot       */
+  s32i a6, a1, 24       /* ...                                                */
+  s32i a7, a1, 28       /* ...                                                */
+  mov a3, a2            /* print() wants the formatting string as arg 2 too   */
+  movi a2, 0            /* and a zero for its first arg                       */
+  addi a4, a1, 8        /* third arg is the pointer to the argument array     */
+  mov a5, a4            /* as is the fourth arg                               */
+  movi a6, 4            /* and the fifth arg is 4  (https://xkcd.com/221/ ?)  */
+  call0 print           /* do it!                                             */
+  l32i a0, a1, 0        /* restore return address into a0                     */
+  addi a1, a1, 32       /* release the stack                                  */
+  ret                   /* all done                                           */