build system: add option to place statics in .bss

Upstream BusyBox uses the '-fdata-sections' compiler flag.  On
Windows this has the unfortunate side effect that static variables
are placed in the .data section, thus increasing the size of the
binary.

Add a configuration option, STATICS_IN_BSS, to force statics into
.bss on Windows, saving 2-5KB for most binaries.  It has no
effect on POSIX builds, where statics are always placed in .bss.

7 files changed, 19 insertions, 0 deletions

diff --git a/Config.in b/Config.in
index 51de85284..33fdd4466 100644
--- a/Config.in
+++ b/Config.in
@@ -582,6 +582,16 @@ config UNWIND_TABLES
         normally required in BusyBox, but Windows' Control Flow Guard
         needs it.  Disabling this reduces the size of the binaries.
 
+config STATICS_IN_BSS
+        bool "Place static variables in .bss"
+        default y
+        depends on PLATFORM_MINGW32
+        help
+        Upstream BusyBox sets a compiler flag which results in static
+        variables being placed in the .data section on Windows, thus
+        increasing the size of the binary. Disable this setting to use
+        the upstream default, probably only for diagnostic purposes.
+
 comment 'Build Options'
 
 config STATIC
diff --git a/Makefile.flags b/Makefile.flags
index 29fabcfb5..37200c89a 100644
--- a/Makefile.flags
+++ b/Makefile.flags
@@ -54,7 +54,11 @@ ifneq ($(lastword $(subst -, ,$(CC))),clang)
 CFLAGS += $(call cc-option,-finline-limit=0,)
 endif
 
+ifneq ($(CONFIG_STATICS_IN_BSS),y)
 CFLAGS += $(call cc-option,-fno-builtin-strlen -fomit-frame-pointer -ffunction-sections -fdata-sections,)
+else
+CFLAGS += $(call cc-option,-fno-builtin-strlen -fomit-frame-pointer -ffunction-sections,)
+endif
 # -fno-guess-branch-probability: prohibit pseudo-random guessing
 # of branch probabilities (hopefully makes bloatcheck more stable):
 CFLAGS += $(call cc-option,-fno-guess-branch-probability,)
diff --git a/configs/mingw32_defconfig b/configs/mingw32_defconfig
index d63a65eda..4f7da4ec3 100644
--- a/configs/mingw32_defconfig
+++ b/configs/mingw32_defconfig
@@ -66,6 +66,7 @@ CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_OVERRIDE_APPLETS=""
 # CONFIG_UNWIND_TABLES is not set
+CONFIG_STATICS_IN_BSS=y
 
 #
 # Build Options
diff --git a/configs/mingw32w_defconfig b/configs/mingw32w_defconfig
index 2e8172246..f0da4060e 100644
--- a/configs/mingw32w_defconfig
+++ b/configs/mingw32w_defconfig
@@ -66,6 +66,7 @@ CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_OVERRIDE_APPLETS=""
 # CONFIG_UNWIND_TABLES is not set
+CONFIG_STATICS_IN_BSS=y
 
 #
 # Build Options
diff --git a/configs/mingw64_defconfig b/configs/mingw64_defconfig
index f2b788bf7..e667571e1 100644
--- a/configs/mingw64_defconfig
+++ b/configs/mingw64_defconfig
@@ -66,6 +66,7 @@ CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_OVERRIDE_APPLETS=""
 CONFIG_UNWIND_TABLES=y
+CONFIG_STATICS_IN_BSS=y
 
 #
 # Build Options
diff --git a/configs/mingw64a_defconfig b/configs/mingw64a_defconfig
index 4e82560d7..b5b7a7a52 100644
--- a/configs/mingw64a_defconfig
+++ b/configs/mingw64a_defconfig
@@ -66,6 +66,7 @@ CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_OVERRIDE_APPLETS=""
 # CONFIG_UNWIND_TABLES is not set
+CONFIG_STATICS_IN_BSS=y
 
 #
 # Build Options
diff --git a/configs/mingw64u_defconfig b/configs/mingw64u_defconfig
index 08df0a86e..b3780040d 100644
--- a/configs/mingw64u_defconfig
+++ b/configs/mingw64u_defconfig
@@ -66,6 +66,7 @@ CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_OVERRIDE_APPLETS=""
 CONFIG_UNWIND_TABLES=y
+CONFIG_STATICS_IN_BSS=y
 
 #
 # Build Options