redirect the floating-point capable vfprintf / vfscanf symbols to picolibc's integer-only variant (#24720)

pio-tools/picolibc_flags.py

@@ -0,0 +1,26 @@
+#
+# Picolibc-specific linker flags.
+#
+# When the Arduino ESP32 framework is built against picolibc (detected via
+# `-specs=picolibc.specs`), redirect the floating-point capable vfprintf / vfscanf
+# symbols to picolibc's integer-only variants (__i_vfprintf / __i_vfscanf).
+# This drops the float/double formatting code path from the firmware and saves
+# a noticeable amount of flash.
+#
+
+Import("env")
+
+
+def _picolibc_in_use(env):
+    for var in ("CCFLAGS", "CFLAGS", "CXXFLAGS", "LINKFLAGS"):
+        for flag in env.get(var, []):
+            if "picolibc.specs" in str(flag):
+                return True
+    return False
+
+
+if _picolibc_in_use(env):
+    env.Append(LINKFLAGS=[
+        "-Wl,--defsym=vfprintf=__i_vfprintf",
+        "-Wl,--defsym=vfscanf=__i_vfscanf",
+    ])