diff --git a/os/ports/GCC/ARMCMx/crt0.c b/os/ports/GCC/ARMCMx/crt0.c
index bb8d3830d..4ac08ecdb 100644
--- a/os/ports/GCC/ARMCMx/crt0.c
+++ b/os/ports/GCC/ARMCMx/crt0.c
@@ -33,6 +33,17 @@ typedef funcp_t * funcpp_t;
 
 #define SYMVAL(sym) (uint32_t)(((uint8_t *)&(sym)) - ((uint8_t *)0))
 
+/*
+ * Area fill code, it is a macro because here functions cannot be called
+ * until stacks are initialized.
+ */
+#define fill32(start, end, filler) {                                        \
+  uint32_t *p1 = start;                                                     \
+  uint32_t *p2 = end;                                                       \
+  while (p1 < p2)                                                           \
+    *p1++ = filler;                                                         \
+}
+
 /*===========================================================================*/
 /**
  * @name    Startup settings
@@ -227,19 +238,6 @@ void _default_exit(void) {
     ;
 }
 
-/**
- * @brief   Memory fill.
- *
- * @param[in] start     fill area start
- * @param[in] end       fill area end
- * @param[in] filler    filler pattern
- */
-static void fill32(uint32_t *start, uint32_t *end, uint32_t filler) {
-
-  while (start < end)
-    *start++ = filler;
-}
-
 /**
  * @brief   Reset vector.
  */
diff --git a/readme.txt b/readme.txt
index cea1f5e48..7c45db6e4 100644
--- a/readme.txt
+++ b/readme.txt
@@ -83,6 +83,8 @@
 *****************************************************************************
 
 *** 2.5.1 ***
+- FIX: Fixed ARM CMx crt0.c fails at low optimization levels (bug 3578927)
+  (backported to 2.4.3).
 - FIX: Fixed compilation issue in chregistry.c (bug 3576776).
 - FIX: Fixed compilation issue in syscalls.c (bug 3576771)(backported
   to 2.4.3).
diff --git a/todo.txt b/todo.txt
index aceaf6c79..12dd9102c 100644
--- a/todo.txt
+++ b/todo.txt
@@ -5,18 +5,7 @@ X = In progress, some work done.
 ? = Not sure if worth the effort or useful at all.
 N = Decided against.
 
-Version 2.5.0
-* SDC driver port to STM32F2 and STM32F4.
-* Revision of scheduling strategy for threads at equal priority.
-* Handling of Virtual Timer callbacks out of critical zone.
-* Add normal API (not iclass) variants of the VT functions.
-* MMC_SPI driver speedup.
-* FatFs 0.9x integration.
-* USB driver model revision.
-  * STM32 OTG USB cell support for CL, F2, F4 devices.
-* CAN driver test on STM32F2/F4.
-* STM32F0 support.
-  * Specific ADC driver for STM32F0.
+Version 2.5.1
 
 Within 2.5.x:
 X Revision of the RTCv2 driver implementation.