discard unused functions at link time

Put each functions in a separate section by using -ffunction-sections,
then discard the non-referenced ones in the linker with -gc-sections.
Force keeping a few special symbols by using the KEEP() linker
directive.

This modification is not saving a lot of spaces per se, but will enable
larger code pruning with future optional features.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=none
TEST=make buildall, manually check discarded symbols in the .map file
and run on Spring and Link.
The size delta is the following:
Link: total 85.7k -> 84.9k (.text 60.3k -> 59.5k)
Spring: total 59.2k -> 57.2k  (.text 44.4k -> 42.5k)

Change-Id: Ib6eb0d3f2cc4fc172c9fc26acac2e486921690a3
Reviewed-on: https://chromium-review.googlesource.com/189224
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>

4 files changed, 65 insertions, 64 deletions

diff --git a/Makefile.toolchain b/Makefile.toolchain
index 6d44331fc7..dd0ebb2174 100644
--- a/Makefile.toolchain
+++ b/Makefile.toolchain
@@ -40,6 +40,7 @@ CFLAGS_DEFINE=-DOUTDIR=$(out) -DCHIP=$(CHIP) -DBOARD_TASKFILE=ec.tasklist \
 CPPFLAGS=$(CFLAGS_DEFINE) $(CFLAGS_INCLUDE) $(CFLAGS_TEST) \
 	 $(EXTRA_CFLAGS) $(CFLAGS_COVERAGE)
 CFLAGS=$(CPPFLAGS) $(CFLAGS_CPU) $(CFLAGS_DEBUG) $(CFLAGS_WARN) $(CFLAGS_y)
+CFLAGS+= -ffunction-sections
 
 FTDIVERSION=$(shell $(PKG_CONFIG) --modversion libftdi1 2>/dev/null)
 ifneq ($(FTDIVERSION),)
@@ -53,7 +54,7 @@ LIBFTDI_LDLIBS=$(shell $(PKG_CONFIG) --libs   lib${LIBFTDI_NAME})
 
 BUILD_CFLAGS= $(LIBFTDI_CFLAGS) $(CPPFLAGS) -O3 $(CFLAGS_DEBUG) $(CFLAGS_WARN)
 HOST_CFLAGS=$(CPPFLAGS) -O3 $(CFLAGS_DEBUG) $(CFLAGS_WARN)
-LDFLAGS=-nostdlib -X
+LDFLAGS=-nostdlib -X --gc-sections
 BUILD_LDFLAGS=$(LIBFTDI_LDLIBS)
 HOST_TEST_LDFLAGS=-T core/host/host_exe.lds -lrt -pthread -rdynamic -lm\
 		  $(if $(TEST_COVERAGE),-fprofile-arcs,)
diff --git a/core/cortex-m/ec.lds.S b/core/cortex-m/ec.lds.S
index c0c87e1343..e345bc93ca 100644
--- a/core/cortex-m/ec.lds.S
+++ b/core/cortex-m/ec.lds.S
@@ -25,7 +25,7 @@ SECTIONS
         OUTDIR/core/CORE/init.o (.text.vecttable)
         . = ALIGN(4);
         __version_struct_offset = .;
-        *(.rodata.ver)
+        KEEP(*(.rodata.ver))
 #ifdef SHIFT_CODE_FOR_TEST
         . = ALIGN(256);
 #else
@@ -42,82 +42,82 @@ SECTIONS
     .rodata : {
 	/* Symbols defined here are declared in link_defs.h */
         __irqprio = .;
-        *(.rodata.irqprio)
+        KEEP(*(.rodata.irqprio))
         __irqprio_end = .;
 
         . = ALIGN(4);
         __cmds = .;
-        *(SORT(.rodata.cmds*))
+        KEEP(*(SORT(.rodata.cmds*)))
         __cmds_end = .;
 
         . = ALIGN(4);
         __hcmds = .;
-        *(.rodata.hcmds)
+        KEEP(*(.rodata.hcmds))
         __hcmds_end = .;
 
         . = ALIGN(4);
         __hooks_init = .;
-        *(.rodata.HOOK_INIT)
+        KEEP(*(.rodata.HOOK_INIT))
         __hooks_init_end = .;
 
         __hooks_pre_freq_change = .;
-        *(.rodata.HOOK_PRE_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_PRE_FREQ_CHANGE))
         __hooks_pre_freq_change_end = .;
 
         __hooks_freq_change = .;
-        *(.rodata.HOOK_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_FREQ_CHANGE))
         __hooks_freq_change_end = .;
 
         __hooks_sysjump = .;
-        *(.rodata.HOOK_SYSJUMP)
+        KEEP(*(.rodata.HOOK_SYSJUMP))
         __hooks_sysjump_end = .;
 
         __hooks_chipset_pre_init = .;
-        *(.rodata.HOOK_CHIPSET_PRE_INIT)
+        KEEP(*(.rodata.HOOK_CHIPSET_PRE_INIT))
         __hooks_chipset_pre_init_end = .;
 
         __hooks_chipset_startup = .;
-        *(.rodata.HOOK_CHIPSET_STARTUP)
+        KEEP(*(.rodata.HOOK_CHIPSET_STARTUP))
         __hooks_chipset_startup_end = .;
 
         __hooks_chipset_resume = .;
-        *(.rodata.HOOK_CHIPSET_RESUME)
+        KEEP(*(.rodata.HOOK_CHIPSET_RESUME))
         __hooks_chipset_resume_end = .;
 
         __hooks_chipset_suspend = .;
-        *(.rodata.HOOK_CHIPSET_SUSPEND)
+        KEEP(*(.rodata.HOOK_CHIPSET_SUSPEND))
         __hooks_chipset_suspend_end = .;
 
         __hooks_chipset_shutdown = .;
-        *(.rodata.HOOK_CHIPSET_SHUTDOWN)
+        KEEP(*(.rodata.HOOK_CHIPSET_SHUTDOWN))
         __hooks_chipset_shutdown_end = .;
 
         __hooks_ac_change = .;
-        *(.rodata.HOOK_AC_CHANGE)
+        KEEP(*(.rodata.HOOK_AC_CHANGE))
         __hooks_ac_change_end = .;
 
         __hooks_lid_change = .;
-        *(.rodata.HOOK_LID_CHANGE)
+        KEEP(*(.rodata.HOOK_LID_CHANGE))
         __hooks_lid_change_end = .;
 
         __hooks_pwrbtn_change = .;
-        *(.rodata.HOOK_POWER_BUTTON_CHANGE)
+        KEEP(*(.rodata.HOOK_POWER_BUTTON_CHANGE))
         __hooks_pwrbtn_change_end = .;
 
         __hooks_charge_state_change = .;
-        *(.rodata.HOOK_CHARGE_STATE_CHANGE)
+        KEEP(*(.rodata.HOOK_CHARGE_STATE_CHANGE))
         __hooks_charge_state_change_end = .;
 
         __hooks_tick = .;
-        *(.rodata.HOOK_TICK)
+        KEEP(*(.rodata.HOOK_TICK))
         __hooks_tick_end = .;
 
         __hooks_second = .;
-        *(.rodata.HOOK_SECOND)
+        KEEP(*(.rodata.HOOK_SECOND))
         __hooks_second_end = .;
 
         __deferred_funcs = .;
-        *(.rodata.deferred)
+        KEEP(*(.rodata.deferred))
         __deferred_funcs_end = .;
 
         . = ALIGN(4);
@@ -125,7 +125,7 @@ SECTIONS
 
 #if defined(SECTION_IS_RO) && defined(CONFIG_FLASH)
         . = ALIGN(64);
-        *(.google)
+        KEEP(*(.google))
 #endif
         . = ALIGN(4);
 #ifdef COMPILE_FOR_RAM
diff --git a/core/cortex-m0/ec.lds.S b/core/cortex-m0/ec.lds.S
index ac05bbc333..28e52869f8 100644
--- a/core/cortex-m0/ec.lds.S
+++ b/core/cortex-m0/ec.lds.S
@@ -25,7 +25,7 @@ SECTIONS
         OUTDIR/core/CORE/init.o (.text.vecttable)
         . = ALIGN(4);
         __version_struct_offset = .;
-        *(.rodata.ver)
+        KEEP(*(.rodata.ver))
 #ifdef SHIFT_CODE_FOR_TEST
         . = ALIGN(256);
 #else
@@ -42,82 +42,82 @@ SECTIONS
     .rodata : {
 	/* Symbols defined here are declared in link_defs.h */
         __irqprio = .;
-        *(.rodata.irqprio)
+        KEEP(*(.rodata.irqprio))
         __irqprio_end = .;
 
         . = ALIGN(4);
         __cmds = .;
-        *(SORT(.rodata.cmds*))
+        KEEP(*(SORT(.rodata.cmds*)))
         __cmds_end = .;
 
         . = ALIGN(4);
         __hcmds = .;
-        *(.rodata.hcmds)
+        KEEP(*(.rodata.hcmds))
         __hcmds_end = .;
 
         . = ALIGN(4);
         __hooks_init = .;
-        *(.rodata.HOOK_INIT)
+        KEEP(*(.rodata.HOOK_INIT))
         __hooks_init_end = .;
 
         __hooks_pre_freq_change = .;
-        *(.rodata.HOOK_PRE_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_PRE_FREQ_CHANGE))
         __hooks_pre_freq_change_end = .;
 
         __hooks_freq_change = .;
-        *(.rodata.HOOK_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_FREQ_CHANGE))
         __hooks_freq_change_end = .;
 
         __hooks_sysjump = .;
-        *(.rodata.HOOK_SYSJUMP)
+        KEEP(*(.rodata.HOOK_SYSJUMP))
         __hooks_sysjump_end = .;
 
         __hooks_chipset_pre_init = .;
-        *(.rodata.HOOK_CHIPSET_PRE_INIT)
+        KEEP(*(.rodata.HOOK_CHIPSET_PRE_INIT))
         __hooks_chipset_pre_init_end = .;
 
         __hooks_chipset_startup = .;
-        *(.rodata.HOOK_CHIPSET_STARTUP)
+        KEEP(*(.rodata.HOOK_CHIPSET_STARTUP))
         __hooks_chipset_startup_end = .;
 
         __hooks_chipset_resume = .;
-        *(.rodata.HOOK_CHIPSET_RESUME)
+        KEEP(*(.rodata.HOOK_CHIPSET_RESUME))
         __hooks_chipset_resume_end = .;
 
         __hooks_chipset_suspend = .;
-        *(.rodata.HOOK_CHIPSET_SUSPEND)
+        KEEP(*(.rodata.HOOK_CHIPSET_SUSPEND))
         __hooks_chipset_suspend_end = .;
 
         __hooks_chipset_shutdown = .;
-        *(.rodata.HOOK_CHIPSET_SHUTDOWN)
+        KEEP(*(.rodata.HOOK_CHIPSET_SHUTDOWN))
         __hooks_chipset_shutdown_end = .;
 
         __hooks_ac_change = .;
-        *(.rodata.HOOK_AC_CHANGE)
+        KEEP(*(.rodata.HOOK_AC_CHANGE))
         __hooks_ac_change_end = .;
 
         __hooks_lid_change = .;
-        *(.rodata.HOOK_LID_CHANGE)
+        KEEP(*(.rodata.HOOK_LID_CHANGE))
         __hooks_lid_change_end = .;
 
         __hooks_pwrbtn_change = .;
-        *(.rodata.HOOK_POWER_BUTTON_CHANGE)
+        KEEP(*(.rodata.HOOK_POWER_BUTTON_CHANGE))
         __hooks_pwrbtn_change_end = .;
 
         __hooks_charge_state_change = .;
-        *(.rodata.HOOK_CHARGE_STATE_CHANGE)
+        KEEP(*(.rodata.HOOK_CHARGE_STATE_CHANGE))
         __hooks_charge_state_change_end = .;
 
         __hooks_tick = .;
-        *(.rodata.HOOK_TICK)
+        KEEP(*(.rodata.HOOK_TICK))
         __hooks_tick_end = .;
 
         __hooks_second = .;
-        *(.rodata.HOOK_SECOND)
+        KEEP(*(.rodata.HOOK_SECOND))
         __hooks_second_end = .;
 
         __deferred_funcs = .;
-        *(.rodata.deferred)
+        KEEP(*(.rodata.deferred))
         __deferred_funcs_end = .;
 
         . = ALIGN(4);
@@ -125,7 +125,7 @@ SECTIONS
 
 #if defined(SECTION_IS_RO) && defined(CONFIG_FLASH)
         . = ALIGN(64);
-        *(.google)
+        KEEP(*(.google))
 #endif
         . = ALIGN(4);
 #ifdef COMPILE_FOR_RAM
diff --git a/core/nds32/ec.lds.S b/core/nds32/ec.lds.S
index f1d021c3b0..84e08d34bc 100644
--- a/core/nds32/ec.lds.S
+++ b/core/nds32/ec.lds.S
@@ -25,7 +25,7 @@ SECTIONS
         OUTDIR/core/CORE/init.o (.text.vecttable)
         . = ALIGN(4);
         __version_struct_offset = .;
-        *(.rodata.ver)
+        KEEP(*(.rodata.ver))
 #ifdef SHIFT_CODE_FOR_TEST
         . = ALIGN(256);
 #else
@@ -43,7 +43,7 @@ SECTIONS
     .rodata :  {
         /* Symbols defined here are declared in link_defs.h */
         __irqprio = .;
-        *(.rodata.irqprio)
+        KEEP(*(.rodata.irqprio))
         __irqprio_end = .;
 
         . = ALIGN(4);
@@ -52,77 +52,77 @@ SECTIONS
 
         . = ALIGN(4);
         __cmds = .;
-        *(SORT(.rodata.cmds*))
+        KEEP(*(SORT(.rodata.cmds*)))
         __cmds_end = .;
 
         . = ALIGN(4);
         __hcmds = .;
-        *(.rodata.hcmds)
+        KEEP(*(.rodata.hcmds))
         __hcmds_end = .;
 
         . = ALIGN(4);
         __hooks_init = .;
-        *(.rodata.HOOK_INIT)
+        KEEP(*(.rodata.HOOK_INIT))
         __hooks_init_end = .;
 
         __hooks_pre_freq_change = .;
-        *(.rodata.HOOK_PRE_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_PRE_FREQ_CHANGE))
         __hooks_pre_freq_change_end = .;
 
         __hooks_freq_change = .;
-        *(.rodata.HOOK_FREQ_CHANGE)
+        KEEP(*(.rodata.HOOK_FREQ_CHANGE))
         __hooks_freq_change_end = .;
 
         __hooks_sysjump = .;
-        *(.rodata.HOOK_SYSJUMP)
+        KEEP(*(.rodata.HOOK_SYSJUMP))
         __hooks_sysjump_end = .;
 
         __hooks_chipset_pre_init = .;
-        *(.rodata.HOOK_CHIPSET_PRE_INIT)
+        KEEP(*(.rodata.HOOK_CHIPSET_PRE_INIT))
         __hooks_chipset_pre_init_end = .;
 
         __hooks_chipset_startup = .;
-        *(.rodata.HOOK_CHIPSET_STARTUP)
+        KEEP(*(.rodata.HOOK_CHIPSET_STARTUP))
         __hooks_chipset_startup_end = .;
 
         __hooks_chipset_resume = .;
-        *(.rodata.HOOK_CHIPSET_RESUME)
+        KEEP(*(.rodata.HOOK_CHIPSET_RESUME))
         __hooks_chipset_resume_end = .;
 
         __hooks_chipset_suspend = .;
-        *(.rodata.HOOK_CHIPSET_SUSPEND)
+        KEEP(*(.rodata.HOOK_CHIPSET_SUSPEND))
         __hooks_chipset_suspend_end = .;
 
         __hooks_chipset_shutdown = .;
-        *(.rodata.HOOK_CHIPSET_SHUTDOWN)
+        KEEP(*(.rodata.HOOK_CHIPSET_SHUTDOWN))
         __hooks_chipset_shutdown_end = .;
 
         __hooks_ac_change = .;
-        *(.rodata.HOOK_AC_CHANGE)
+        KEEP(*(.rodata.HOOK_AC_CHANGE))
         __hooks_ac_change_end = .;
 
         __hooks_lid_change = .;
-        *(.rodata.HOOK_LID_CHANGE)
+        KEEP(*(.rodata.HOOK_LID_CHANGE))
         __hooks_lid_change_end = .;
 
         __hooks_pwrbtn_change = .;
-        *(.rodata.HOOK_POWER_BUTTON_CHANGE)
+        KEEP(*(.rodata.HOOK_POWER_BUTTON_CHANGE))
         __hooks_pwrbtn_change_end = .;
 
         __hooks_charge_state_change = .;
-        *(.rodata.HOOK_CHARGE_STATE_CHANGE)
+        KEEP(*(.rodata.HOOK_CHARGE_STATE_CHANGE))
         __hooks_charge_state_change_end = .;
 
         __hooks_tick = .;
-        *(.rodata.HOOK_TICK)
+        KEEP(*(.rodata.HOOK_TICK))
         __hooks_tick_end = .;
 
         __hooks_second = .;
-        *(.rodata.HOOK_SECOND)
+        KEEP(*(.rodata.HOOK_SECOND))
         __hooks_second_end = .;
 
         __deferred_funcs = .;
-        *(.rodata.deferred)
+        KEEP(*(.rodata.deferred))
         __deferred_funcs_end = .;
 
         . = ALIGN(4);
@@ -130,7 +130,7 @@ SECTIONS
 
 #if defined(SECTION_IS_RO) && defined(CONFIG_FLASH)
         . = ALIGN(64);
-        *(.google)
+        KEEP(*(.google))
 #endif
         . = ALIGN(4);
 #ifdef COMPILE_FOR_RAM