lto experiment

core/SConscript.boardloader

@@ -102,6 +102,7 @@ env.Replace(
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
+    '-flto=2 '
     + env.get('ENV')["CPU_CCFLAGS"] + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/boardloader/memory.ld -Wl,--gc-sections -Wl,-Map=build/boardloader/boardloader.map -Wl,--warn-common  -Wl,--print-memory-usage',

core/SConscript.bootloader

@@ -146,6 +146,7 @@ env.Replace(
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
+    '-flto=2 '
     +  env.get('ENV')["CPU_CCFLAGS"] + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/bootloader/memory.ld -Wl,--gc-sections -Wl,-Map=build/bootloader/bootloader.map -Wl,--warn-common -Wl,--print-memory-usage',

core/SConscript.firmware

@@ -434,6 +434,7 @@ env.Replace(
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
+    '-flto=2 '
     +  env.get('ENV')["CPU_CCFLAGS"] + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/firmware/memory_${TREZOR_MODEL}%s.ld -Wl,--gc-sections  -Wl,--print-memory-usage -Wl,-Map=build/firmware/firmware.map -Wl,--warn-common' % LD_VARIANT,

core/embed/trezorhal/stm32f4/common.c

@@ -188,7 +188,7 @@ void clear_otg_hs_memory(void) {
 
 uint32_t __stack_chk_guard = 0;
 
-void __attribute__((noreturn)) __stack_chk_fail(void) {
+void __attribute__((noreturn, used)) __stack_chk_fail(void) {
   error_shutdown("INTERNAL ERROR", "(SS)");
 }