From 04db37a34ac43d0a9c5fb8c807b56ed58a551bce Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 26 Feb 2026 20:38:38 -0700
Subject: [PATCH] [esp8266] Remove forced scanf linkage to save ~8KB flash
 (#13678)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
---
 esphome/components/esp8266/__init__.py        |  6 +++
 .../esp8266/remove_float_scanf.py.script      | 46 +++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 esphome/components/esp8266/remove_float_scanf.py.script

diff --git a/esphome/components/esp8266/__init__.py b/esphome/components/esp8266/__init__.py
index c7b5d5c130..927a59fd61 100644
--- a/esphome/components/esp8266/__init__.py
+++ b/esphome/components/esp8266/__init__.py
@@ -205,6 +205,7 @@ async def to_code(config):
             "pre:testing_mode.py",
             "pre:exclude_updater.py",
             "pre:exclude_waveform.py",
+            "pre:remove_float_scanf.py",
             "post:post_build.py",
         ],
     )
@@ -342,3 +343,8 @@ def copy_files() -> None:
         exclude_waveform_file,
         CORE.relative_build_path("exclude_waveform.py"),
     )
+    remove_float_scanf_file = dir / "remove_float_scanf.py.script"
+    copy_file_if_changed(
+        remove_float_scanf_file,
+        CORE.relative_build_path("remove_float_scanf.py"),
+    )
diff --git a/esphome/components/esp8266/remove_float_scanf.py.script b/esphome/components/esp8266/remove_float_scanf.py.script
new file mode 100644
index 0000000000..b1d03a4d46
--- /dev/null
+++ b/esphome/components/esp8266/remove_float_scanf.py.script
@@ -0,0 +1,46 @@
+# pylint: disable=E0602
+Import("env")  # noqa
+
+# Remove forced scanf linkage to allow garbage collection of unused code
+#
+# The ESP8266 Arduino framework unconditionally adds:
+#   -u _printf_float -u _scanf_float
+#
+# The -u flag forces symbols to be linked even if unreferenced, which pulls
+# in the entire scanf family (~7-8KB). ESPHome doesn't use scanf at all
+# (verified by CI check in PR #13657), so this is pure dead weight.
+#
+# By removing -u _scanf_float, --gc-sections can eliminate:
+#   - scanf family functions (~7KB)
+#   - _strtod_l (~3.7KB)
+#   - Related parsing infrastructure
+#
+# We keep -u _printf_float because components still use %f in logging.
+
+
+def remove_scanf_float_flag(source, target, env):
+    """Remove -u _scanf_float from linker flags.
+
+    This is called as a pre-action before the link step, after the
+    Arduino framework has added its default flags.
+    """
+    linkflags = env.get("LINKFLAGS", [])
+    new_linkflags = []
+    i = 0
+
+    while i < len(linkflags):
+        flag = linkflags[i]
+        if flag == "-u" and i + 1 < len(linkflags):
+            next_flag = linkflags[i + 1]
+            if next_flag == "_scanf_float":
+                print("ESPHome: Removing _scanf_float (saves ~8KB flash)")
+                i += 2  # Skip both -u and the symbol
+                continue
+        new_linkflags.append(flag)
+        i += 1
+
+    env.Replace(LINKFLAGS=new_linkflags)
+
+
+# Register the callback to run before the link step
+env.AddPreAction("$BUILD_DIR/${PROGNAME}.elf", remove_scanf_float_flag)