examples/natmod/btree: Fix build on RV32 with Picolibc.

agatti · dpgeorge · commit b63e5280765d · 2025-07-20T23:03:40.000+10:00
This commit fixes building the "btree" example natmod on RV32 when
Picolibc is being used and uses thread-local storage for storing the
errno variable.

The fix is surprisingly simple: Picolibc allows overriding the function
that will provide a pointer to the "errno" variable, and the btree
natmod integration code already has all of this machinery set up as part
of its library integration.  Redirecting Picolibc to the already
existing pointer provider function via a compile-time definition is
enough to let the module compile and pass QEMU tests.

This workaround will work on any Picolibc versions (Arm, RV32, Xtensa,
etc.) even if TLS support was not enabled to begin with, and will
effectively do nothing if the toolchain used will rely on Newlib to
provide standard C library functions.

Given that the btree module now builds and passes the relevant natmod
tests, said module is now part of the QEMU port's natmod testing
procedure, and CI now will build the btree module for RV32 as part to
its checks.

Signed-off-by: Alessandro Gatti &lt;a.gatti@frob.it&gt;
diff --git a/examples/natmod/btree/Makefile b/examples/natmod/btree/Makefile
@@ -36,6 +36,9 @@ ifeq ($(ARCH),xtensa)
 MPY_EXTERN_SYM_FILE=$(MPY_DIR)/ports/esp8266/boards/eagle.rom.addr.v6.ld
 endif
 
+# Use our own errno implementation if Picolibc is used
+CFLAGS += -D__PICOLIBC_ERRNO_FUNCTION=__errno
+
 include $(MPY_DIR)/py/dynruntime.mk
 
 # btree needs gnu99 defined
diff --git a/ports/qemu/Makefile b/ports/qemu/Makefile
@@ -191,12 +191,11 @@ test_full: $(BUILD)/firmware.elf
 	cd $(TOP)/tests && ./run-tests.py $(RUN_TESTS_FULL_ARGS) --via-mpy
 	cd $(TOP)/tests && ./run-tests.py $(RUN_TESTS_FULL_ARGS) --via-mpy --emit native
 
-# "btree" currently does not build for rv32imc (Picolibc TLS incompatibility).
 .PHONY: test_natmod
 test_natmod: $(BUILD)/firmware.elf
 	$(eval DIRNAME=ports/$(notdir $(CURDIR)))
 	cd $(TOP)/tests && \
-		for natmod in deflate framebuf heapq random_basic re; do \
+		for natmod in btree deflate framebuf heapq random_basic re; do \
 		./run-natmodtests.py -p -d execpty:"$(QEMU_SYSTEM) $(QEMU_ARGS) -serial pty -kernel ../$(DIRNAME)/$<" extmod/$$natmod*.py; \
 		done
 
diff --git a/tools/ci.sh b/tools/ci.sh
@@ -563,7 +563,7 @@ function ci_native_mpy_modules_build {
     else
         arch=$1
     fi
-    for natmod in deflate features1 features3 features4 framebuf heapq random re
+    for natmod in btree deflate features1 features3 features4 framebuf heapq random re
     do
         make -C examples/natmod/$natmod ARCH=$arch clean
         make -C examples/natmod/$natmod ARCH=$arch
@@ -576,12 +576,6 @@ function ci_native_mpy_modules_build {
     else
         make -C examples/natmod/features2 ARCH=$arch
     fi
-
-    # btree requires thread local storage support on rv32imc.
-    if [ $arch != "rv32imc" ]; then
-        make -C examples/natmod/btree ARCH=$arch clean
-        make -C examples/natmod/btree ARCH=$arch
-    fi
 }
 
 function ci_native_mpy_modules_32bit_build {
