From d1b66a08c1d9838b139e9fef6cc2d38e5d5ee57d Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@espressif.com>
Date: Fri, 30 Jun 2017 17:14:50 +1000
Subject: [PATCH] bootloader: Add option to build with Link Time Optimisation
 enabled

---
 components/bootloader/Kconfig.projbuild             | 13 +++++++++++--
 .../bootloader/subproject/main/Makefile.projbuild   |  5 +++++
 make/project.mk                                     |  2 +-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/components/bootloader/Kconfig.projbuild b/components/bootloader/Kconfig.projbuild
index 5af223c0ad..b4f2c904ac 100644
--- a/components/bootloader/Kconfig.projbuild
+++ b/components/bootloader/Kconfig.projbuild
@@ -43,7 +43,16 @@ config BOOTLOADER_SPI_WP_PIN
 
         The default value (GPIO 7) is correct for WP pin on ESP32-D2WD integrated flash.
 
-endmenu  # Bootloader
+config BOOTLOADER_LTO
+       bool "Build bootloader with Link Time Optimisation"
+       default n
+       help
+           Setting this option enables gcc Link Time Optimisation for the bootloader build & link pass.
+
+           This gives a smaller bootloader binary (can be useful if secure boot & flash encryption & logging are all enabled), and can
+           give faster boot times, but it makes the bootloader harder to debug.
+
+endmenu  # Bootloader config
 
 
 menu "Security features"
@@ -217,7 +226,7 @@ config FLASH_ENCRYPTION_UART_BOOTLOADER_ALLOW_CACHE
 config SECURE_BOOT_TEST_MODE
        bool "Secure boot test mode: don't permanently set any efuses"
        depends on SECURE_BOOT_INSECURE
-       default N
+       default n
        help
           If this option is set, all permanent secure boot changes (via Efuse) are disabled.
 
diff --git a/components/bootloader/subproject/main/Makefile.projbuild b/components/bootloader/subproject/main/Makefile.projbuild
index c368c68416..afd5282d83 100644
--- a/components/bootloader/subproject/main/Makefile.projbuild
+++ b/components/bootloader/subproject/main/Makefile.projbuild
@@ -2,3 +2,8 @@
 # paths can be added at this level (we need binary librtc to be
 # available to link bootloader).
 COMPONENT_SUBMODULES += $(IDF_PATH)/components/esp32/lib
+
+ifdef CONFIG_BOOTLOADER_LTO
+CFLAGS += -flto
+EXTRA_LDFLAGS += -Wl,-flto
+endif
diff --git a/make/project.mk b/make/project.mk
index cc439a3582..159a261674 100644
--- a/make/project.mk
+++ b/make/project.mk
@@ -290,7 +290,7 @@ export HOSTCC HOSTLD HOSTAR HOSTOBJCOPY SIZE
 CC := $(call dequote,$(CONFIG_TOOLPREFIX))gcc
 CXX := $(call dequote,$(CONFIG_TOOLPREFIX))c++
 LD := $(call dequote,$(CONFIG_TOOLPREFIX))ld
-AR := $(call dequote,$(CONFIG_TOOLPREFIX))ar
+AR := $(call dequote,$(CONFIG_TOOLPREFIX))gcc-ar
 OBJCOPY := $(call dequote,$(CONFIG_TOOLPREFIX))objcopy
 SIZE := $(call dequote,$(CONFIG_TOOLPREFIX))size
 export CC CXX LD AR OBJCOPY SIZE
-- 
2.40.0