build system: use thread-safe stdio

This makes use of the new bug modeling to declare all platforms that
can use newlib and have no reentrancy hooks as affected by the
non-thread-safe stdio bug. (Which is every platform but ESP* and AVR,
the former because the reentrancy hooks are provided, the latter because
we do not and never will support newlib on them.)

Building on that, the mpaland-printf package is used when newlib is used
and the bug is present. This way we can rely on the stdio being
thread-safe on evyer platform and not causing random crashes at
run time.

Author: maribu

cpu/cortexm_common/Makefile.features

@@ -1,5 +1,6 @@
 FEATURES_PROVIDED += arch_32bit
 FEATURES_PROVIDED += arch_arm
+FEATURES_PROVIDED += bug_newlib_broken_stdio
 FEATURES_PROVIDED += cortexm_svc
 FEATURES_PROVIDED += cpp
 FEATURES_PROVIDED += cpu_check_address
@@ -9,8 +10,8 @@ FEATURES_PROVIDED += libstdcpp
 FEATURES_PROVIDED += newlib
 FEATURES_PROVIDED += periph_flashpage_aux
 FEATURES_PROVIDED += periph_pm
-FEATURES_PROVIDED += puf_sram
 FEATURES_PROVIDED += picolibc
+FEATURES_PROVIDED += puf_sram
 FEATURES_PROVIDED += ssp
 
 # cortex-m33, cortex-m4f and cortex-m7 provide FPU support

cpu/msp430/Makefile.features

@@ -14,6 +14,7 @@ endif
 
 FEATURES_PROVIDED += arch_16bit
 FEATURES_PROVIDED += arch_msp430
+FEATURES_PROVIDED += bug_newlib_broken_stdio
 FEATURES_PROVIDED += cpu_$(CPU_FAM)
 FEATURES_PROVIDED += dbgpin
 FEATURES_PROVIDED += newlib

cpu/riscv_common/Makefile.features

@@ -4,6 +4,7 @@ endif
 
 FEATURES_PROVIDED += arch_32bit
 FEATURES_PROVIDED += arch_riscv
+FEATURES_PROVIDED += bug_newlib_broken_stdio
 FEATURES_PROVIDED += cpp
 FEATURES_PROVIDED += libstdcpp
 FEATURES_PROVIDED += newlib

features.yaml

@@ -925,3 +925,10 @@ groups:
         feature prefixed with "bug_" provided in a build always be used,
         regardless of build configuration.
   features:
+  - name: bug_newlib_broken_stdio
+    help: newlib's stdio is not inherently thread-safe, but depends on the
+          reentrancy hooks to be provided for correct operation. When
+          reentrancy is not enabled, using newlib's stdio is racy, causing
+          random crashes at runtime. Use of this feature will cause an
+          alternative stdio implementation to be used if (and only if) newlib
+          is in used as standard c lib.

makefiles/features_existing.inc.mk

@@ -44,6 +44,7 @@ FEATURES_EXISTING := \
     ble_phy_coded \
     board_bat_voltage \
     bootloader_stm32 \
+    bug_newlib_broken_stdio \
     can_rx_mailbox \
     cortexm_fpu \
     cortexm_mpu \

sys/Makefile.dep

@@ -237,6 +237,13 @@ ifneq (,$(filter newlib,$(USEMODULE)))
       endif
     endif
   endif
+  ifneq (,$(filter bug_newlib_broken_stdio,$(FEATURES_USED)))
+    # work around broken newlib stdio by using alternative stdio implementation,
+    # unless stdio_null is used, which is inherently thread-safe :)
+    ifeq (,$(filter stdio_null,$(USEMODULE)))
+      USEPKG += mpaland-printf
+    endif
+  endif
 endif
 
 ifneq (,$(filter posix_select,$(USEMODULE)))