diff --git a/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/ipc/tfm_spm.c b/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/ipc/tfm_spm.c
index 30210d940b..5ee30a614e 100644
--- a/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/ipc/tfm_spm.c
+++ b/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/ipc/tfm_spm.c
@@ -27,6 +27,7 @@
 #include "region_defs.h"
 #include "tfm_nspm.h"
 #include "tfm_memory_utils.h"
+#include "platform/mbed_toolchain.h"
 
 /*
  * IPC partitions.
@@ -580,7 +581,7 @@ void tfm_spm_init(void)
     tfm_thrd_start_scheduler(&this_thrd);
 }
 
-void tfm_pendsv_do_schedule(struct tfm_state_context_ext *ctxb)
+MBED_USED void tfm_pendsv_do_schedule(struct tfm_state_context_ext *ctxb)
 {
 #if TFM_LVL == 2
     struct spm_partition_desc_t *p_next_partition;
diff --git a/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/tfm_handler.c b/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/tfm_handler.c
index 10a91a56dd..79caca211c 100644
--- a/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/tfm_handler.c
+++ b/components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/tfm_handler.c
@@ -19,6 +19,7 @@
 #include <stdbool.h>
 #include "tfm_svcalls.h"
 #endif
+#include "platform/mbed_toolchain.h"
 
 /* This SVC handler is called when a secure partition requests access to a
  * buffer area
@@ -135,7 +136,7 @@ __attribute__((naked)) void SVC_Handler(void)
 #error "Unsupported ARM Architecture."
 #endif
 
-uint32_t SVCHandler_main(uint32_t *svc_args, uint32_t lr)
+MBED_USED uint32_t SVCHandler_main(uint32_t *svc_args, uint32_t lr)
 {
     uint8_t svc_number;
     /*
diff --git a/platform/source/mbed_alloc_wrappers.cpp b/platform/source/mbed_alloc_wrappers.cpp
index 91c412561b..a3c2844c85 100644
--- a/platform/source/mbed_alloc_wrappers.cpp
+++ b/platform/source/mbed_alloc_wrappers.cpp
@@ -347,6 +347,16 @@ extern "C" void *SUB_REALLOC(void *ptr, size_t size)
         memcpy(new_ptr, (void *)ptr, copy_size);
         free(ptr);
     }
+
+    {
+        volatile uint8_t dummy = 0;
+        if (dummy != 0) { // always false
+            // this code will never be executed
+            // it's just to tell the compiler/linker to preserve SUB_REALLOC symbol
+            // when LTO enabled
+            SUPER_REALLOC(NULL, 0);
+        }
+    }
 #else // #if MBED_HEAP_STATS_ENABLED
     new_ptr = SUPER_REALLOC(ptr, size);
 #endif // #if MBED_HEAP_STATS_ENABLED
@@ -369,6 +379,16 @@ extern "C" void *SUB_CALLOC(size_t nmemb, size_t size)
     if (ptr != NULL) {
         memset(ptr, 0, nmemb * size);
     }
+
+    {
+        volatile uint8_t dummy = 0;
+        if (dummy != 0) { // always false
+            // this code will never be executed
+            // it's just to tell the compiler/linker to preserve SUB_CALLOC symbol
+            // when LTO enabled
+            SUPER_CALLOC(NULL, 0);
+        }
+    }
 #else // #if MBED_HEAP_STATS_ENABLED
     ptr = SUPER_CALLOC(nmemb, size);
 #endif // #if MBED_HEAP_STATS_ENABLED
diff --git a/platform/source/mbed_retarget.cpp b/platform/source/mbed_retarget.cpp
index a234a51764..9eab48fff0 100644
--- a/platform/source/mbed_retarget.cpp
+++ b/platform/source/mbed_retarget.cpp
@@ -1141,7 +1141,7 @@ extern "C" __value_in_regs struct __argc_argv $Sub$$__rt_lib_init(unsigned heapb
 }
 #endif
 
-extern "C" __value_in_regs struct __initial_stackheap __user_setup_stackheap(uint32_t R0, uint32_t R1, uint32_t R2, uint32_t R3)
+MBED_USED extern "C" __value_in_regs struct __initial_stackheap __user_setup_stackheap(uint32_t R0, uint32_t R1, uint32_t R2, uint32_t R3)
 {
     return _mbed_user_setup_stackheap(R0, R1, R2, R3);
 }
diff --git a/targets/TARGET_Analog_Devices/TARGET_ADUCM302X/TARGET_ADUCM3029/TARGET_EV_COG_AD3029LZ/device/startup_ADuCM3029.c b/targets/TARGET_Analog_Devices/TARGET_ADUCM302X/TARGET_ADUCM3029/TARGET_EV_COG_AD3029LZ/device/startup_ADuCM3029.c
index 8bc0ae8289..5ed935626a 100755
--- a/targets/TARGET_Analog_Devices/TARGET_ADUCM302X/TARGET_ADUCM3029/TARGET_EV_COG_AD3029LZ/device/startup_ADuCM3029.c
+++ b/targets/TARGET_Analog_Devices/TARGET_ADUCM302X/TARGET_ADUCM3029/TARGET_EV_COG_AD3029LZ/device/startup_ADuCM3029.c
@@ -62,7 +62,9 @@ extern void SramInit(void);
 
 #if defined( __ICCARM__)
 __root
-#endif /* __ICCARM__ */
+#else
+__attribute__((used))
+#endif
 const uint32_t SECTION_PLACE(blank_checksum[],".checksum") =
 {
     BLANKX60,BLANKX600
@@ -139,6 +141,11 @@ WEAK_FUNCTION( DMA_SIP7_Int_Handler        )
 /*----------------------------------------------------------------------------
   Exception / Interrupt Vector table
  *----------------------------------------------------------------------------*/
+#if defined( __ICCARM__)
+__root
+#else
+__attribute__((used))
+#endif
 const pFunc SECTION_PLACE(IVT_NAME[104],VECTOR_SECTION) =
 {
     (pFunc) INITIAL_SP,    /* Initial Stack Pointer */
diff --git a/targets/TARGET_Analog_Devices/TARGET_ADUCM4X50/TARGET_ADUCM4050/TARGET_EV_COG_AD4050LZ/device/startup_ADuCM4050.c b/targets/TARGET_Analog_Devices/TARGET_ADUCM4X50/TARGET_ADUCM4050/TARGET_EV_COG_AD4050LZ/device/startup_ADuCM4050.c
index c9ff9816e0..96cbd39135 100755
--- a/targets/TARGET_Analog_Devices/TARGET_ADUCM4X50/TARGET_ADUCM4050/TARGET_EV_COG_AD4050LZ/device/startup_ADuCM4050.c
+++ b/targets/TARGET_Analog_Devices/TARGET_ADUCM4X50/TARGET_ADUCM4050/TARGET_EV_COG_AD4050LZ/device/startup_ADuCM4050.c
@@ -60,8 +60,10 @@ extern void SramInit(void);
   Checksum options
  *----------------------------------------------------------------------------*/
 
-#if defined(__ICCARM__)
+#if defined( __ICCARM__)
 __root
+#else
+__attribute__((used))
 #endif
 const uint32_t SECTION_PLACE(blank_checksum[],".checksum") =
 {
@@ -144,6 +146,11 @@ WEAK_FUNCTION( Root_Clk_Err_Handler       )
 /*----------------------------------------------------------------------------
   Exception / Interrupt Vector table
  *----------------------------------------------------------------------------*/
+#if defined( __ICCARM__)
+__root
+#else
+__attribute__((used))
+#endif
 const pFunc SECTION_PLACE(IVT_NAME[104],VECTOR_SECTION) = {
     (pFunc) INITIAL_SP,    /* Initial Stack Pointer */
     ADUCM4050_VECTORS
diff --git a/targets/TARGET_NUVOTON/TARGET_M2351/device/startup_M2351.c b/targets/TARGET_NUVOTON/TARGET_M2351/device/startup_M2351.c
index ad89beaa76..502ba4d259 100644
--- a/targets/TARGET_NUVOTON/TARGET_M2351/device/startup_M2351.c
+++ b/targets/TARGET_NUVOTON/TARGET_M2351/device/startup_M2351.c
@@ -207,7 +207,7 @@ WEAK_ALIAS_FUNC(TRNG_IRQHandler, Default_Handler)       // 101:
 
 /* Vector table */
 #if defined(__ARMCC_VERSION)
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 const uint32_t __vector_table[] @ ".intvec" = {
diff --git a/targets/TARGET_NUVOTON/TARGET_M251/device/startup_M251.c b/targets/TARGET_NUVOTON/TARGET_M251/device/startup_M251.c
index a4e0c39ab0..662c23931d 100644
--- a/targets/TARGET_NUVOTON/TARGET_M251/device/startup_M251.c
+++ b/targets/TARGET_NUVOTON/TARGET_M251/device/startup_M251.c
@@ -155,7 +155,7 @@ WEAK_ALIAS_FUNC(OPA_IRQHandler, Default_Handler)        // 62: OPA Interrupt
 
 /* Vector table */
 #if defined(__ARMCC_VERSION)
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NUVOTON/TARGET_M261/device/startup_M261.c b/targets/TARGET_NUVOTON/TARGET_M261/device/startup_M261.c
index 9af13c61ac..58a328e60d 100644
--- a/targets/TARGET_NUVOTON/TARGET_M261/device/startup_M261.c
+++ b/targets/TARGET_NUVOTON/TARGET_M261/device/startup_M261.c
@@ -193,7 +193,7 @@ WEAK_ALIAS_FUNC(TRNG_IRQHandler, Default_Handler)        // 101:
 
 /* Vector table */
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NUVOTON/TARGET_M451/device/startup_M451Series.c b/targets/TARGET_NUVOTON/TARGET_M451/device/startup_M451Series.c
index 2c4752992e..67b0bd98c2 100644
--- a/targets/TARGET_NUVOTON/TARGET_M451/device/startup_M451Series.c
+++ b/targets/TARGET_NUVOTON/TARGET_M451/device/startup_M451Series.c
@@ -152,7 +152,7 @@ WEAK_ALIAS_FUNC(TK_IRQHandler, Default_Handler)         // 63:
 
 /* Vector table */
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/device/startup_M480.c b/targets/TARGET_NUVOTON/TARGET_M480/device/startup_M480.c
index 792d0eeb31..a851c655ed 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/device/startup_M480.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/device/startup_M480.c
@@ -24,11 +24,13 @@
 #if defined(__CC_ARM)
 #define WEAK            __attribute__ ((weak))
 #define ALIAS(f)        __attribute__ ((weak, alias(#f)))
+#define USED            __attribute__ ((used))
 
 #define WEAK_ALIAS_FUNC(FUN, FUN_ALIAS) \
 void FUN(void) __attribute__ ((weak, alias(#FUN_ALIAS)));
 
 #elif defined(__ICCARM__)
+#define USED            __root
 //#define STRINGIFY(x) #x
 //#define _STRINGIFY(x) STRINGIFY(x)
 #define WEAK_ALIAS_FUNC(FUN, FUN_ALIAS) \
@@ -42,6 +44,7 @@ _Pragma(_STRINGIFY(_WEAK_ALIAS_FUNC(FUN, FUN_ALIAS)))
 #elif defined(__GNUC__)
 #define WEAK            __attribute__ ((weak))
 #define ALIAS(f)        __attribute__ ((weak, alias(#f)))
+#define USED            __attribute__ ((used))
 
 #define WEAK_ALIAS_FUNC(FUN, FUN_ALIAS) \
 void FUN(void) __attribute__ ((weak, alias(#FUN_ALIAS)));
@@ -77,7 +80,7 @@ void Default_Handler(void);
 void Reset_Handler(void);
 void Reset_Handler_1(void);
 void Reset_Handler_2(void);
-void Reset_Handler_Cascade(void *sp, void *pc);
+USED void Reset_Handler_Cascade(void *sp, void *pc);
 
 /* Cortex-M4 core handlers */
 WEAK_ALIAS_FUNC(NMI_Handler, Default_Handler)
@@ -190,7 +193,7 @@ WEAK_ALIAS_FUNC(ETMC_IRQHandler, Default_Handler)       // 95:
 
 /* Vector table */
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NUVOTON/TARGET_NANO100/device/startup_Nano100Series.c b/targets/TARGET_NUVOTON/TARGET_NANO100/device/startup_Nano100Series.c
index da4379dd34..57f1f81e87 100644
--- a/targets/TARGET_NUVOTON/TARGET_NANO100/device/startup_Nano100Series.c
+++ b/targets/TARGET_NUVOTON/TARGET_NANO100/device/startup_Nano100Series.c
@@ -114,7 +114,7 @@ WEAK_ALIAS_FUNC(RTC_IRQHandler, Default_Handler)            // Real time clock i
 
 /* Vector table */
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/device/startup_NUC472_442.c b/targets/TARGET_NUVOTON/TARGET_NUC472/device/startup_NUC472_442.c
index bde25dc172..883d2500ea 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/device/startup_NUC472_442.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/device/startup_NUC472_442.c
@@ -232,7 +232,7 @@ WEAK_ALIAS_FUNC(CRC_IRQHandler, Default_Handler)        // 141: CRC
 
 /* Vector table */
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-__attribute__ ((section("RESET")))
+__attribute__ ((section("RESET"), used))
 const uint32_t __vector_handlers[] = {
 #elif defined(__ICCARM__)
 extern uint32_t CSTACK$$Limit;
diff --git a/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/TARGET_EVK/xip/evkbimxrt1050_flexspi_nor_config.c b/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/TARGET_EVK/xip/evkbimxrt1050_flexspi_nor_config.c
index 3486c84963..1193ad7f37 100644
--- a/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/TARGET_EVK/xip/evkbimxrt1050_flexspi_nor_config.c
+++ b/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/TARGET_EVK/xip/evkbimxrt1050_flexspi_nor_config.c
@@ -17,7 +17,7 @@
  ******************************************************************************/
 #if defined(XIP_BOOT_HEADER_ENABLE) && (XIP_BOOT_HEADER_ENABLE == 1)
 #if defined(__CC_ARM) || defined(__ARMCC_VERSION) || defined(__GNUC__)
-__attribute__((section(".boot_hdr.conf")))
+__attribute__((section(".boot_hdr.conf"), used))
 #elif defined(__ICCARM__)
 #pragma location = ".boot_hdr.conf"
 #endif
diff --git a/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/drivers/fsl_flexspi_nor_boot.c b/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/drivers/fsl_flexspi_nor_boot.c
index 41b273f70b..09a59ed7c7 100644
--- a/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/drivers/fsl_flexspi_nor_boot.c
+++ b/targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_MIMXRT1050/drivers/fsl_flexspi_nor_boot.c
@@ -14,7 +14,7 @@
 
 #if defined(XIP_BOOT_HEADER_ENABLE) && (XIP_BOOT_HEADER_ENABLE == 1)
 #if defined(__CC_ARM) || defined(__ARMCC_VERSION) || defined(__GNUC__)
-    __attribute__((section(".boot_hdr.ivt")))
+    __attribute__((section(".boot_hdr.ivt"), used))
 #elif defined(__ICCARM__)
 #pragma location=".boot_hdr.ivt"
 #endif
diff --git a/targets/TARGET_STM/rtc_api.c b/targets/TARGET_STM/rtc_api.c
index bd03002f7b..52b236bc5f 100644
--- a/targets/TARGET_STM/rtc_api.c
+++ b/targets/TARGET_STM/rtc_api.c
@@ -289,12 +289,12 @@ int rtc_isenabled(void)
 
 #if DEVICE_LPTICKER && !MBED_CONF_TARGET_LPTICKER_LPTIM
 
-static void RTC_IRQHandler(void);
+static void _RTC_IRQHandler(void);
 static void (*irq_handler)(void);
 
 volatile uint8_t lp_Fired = 0;
 
-static void RTC_IRQHandler(void)
+static void _RTC_IRQHandler(void)
 {
     /*  Update HAL state */
     RtcHandle.Instance = RTC;
@@ -428,7 +428,7 @@ void rtc_set_wake_up_timer(timestamp_t timestamp)
     }
 #endif /* RTC_WUTR_WUTOCLR */
 
-    NVIC_SetVector(RTC_WKUP_IRQn, (uint32_t)RTC_IRQHandler);
+    NVIC_SetVector(RTC_WKUP_IRQn, (uint32_t)_RTC_IRQHandler);
     irq_handler = (void (*)(void))lp_ticker_irq_handler;
     NVIC_EnableIRQ(RTC_WKUP_IRQn);
     core_util_critical_section_exit();
@@ -437,7 +437,7 @@ void rtc_set_wake_up_timer(timestamp_t timestamp)
 void rtc_fire_interrupt(void)
 {
     lp_Fired = 1;
-    NVIC_SetVector(RTC_WKUP_IRQn, (uint32_t)RTC_IRQHandler);
+    NVIC_SetVector(RTC_WKUP_IRQn, (uint32_t)_RTC_IRQHandler);
     irq_handler = (void (*)(void))lp_ticker_irq_handler;
     NVIC_SetPendingIRQ(RTC_WKUP_IRQn);
     NVIC_EnableIRQ(RTC_WKUP_IRQn);
diff --git a/targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/TARGET_CC3220SF_LAUNCHXL/CC3220SF_LAUNCHXL.c b/targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/TARGET_CC3220SF_LAUNCHXL/CC3220SF_LAUNCHXL.c
index 6500d968eb..77f80daeb7 100755
--- a/targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/TARGET_CC3220SF_LAUNCHXL/CC3220SF_LAUNCHXL.c
+++ b/targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/TARGET_CC3220SF_LAUNCHXL/CC3220SF_LAUNCHXL.c
@@ -336,7 +336,7 @@ void CC3220SF_LAUNCHXL_initGeneral(void)
 }
 
 #if defined TOOLCHAIN_ARM
-__attribute__((section("signature_section")))
+__attribute__((section("signature_section"), used))
 #elif defined TOOLCHAIN_IAR
 #pragma default_variable_attributes = @ ".dbghdr"
 #elif defined TOOLCHAIN_GCC_ARM
diff --git a/targets/TARGET_TI/TARGET_MSP432/TARGET_MSP432P401R/device/startup_msp432p401r.c b/targets/TARGET_TI/TARGET_MSP432/TARGET_MSP432P401R/device/startup_msp432p401r.c
index 1afa191a34..1ae6f4a667 100644
--- a/targets/TARGET_TI/TARGET_MSP432/TARGET_MSP432P401R/device/startup_msp432p401r.c
+++ b/targets/TARGET_TI/TARGET_MSP432/TARGET_MSP432P401R/device/startup_msp432p401r.c
@@ -156,7 +156,7 @@ WEAK_ALIAS_FUNC(EUSCIB3_SPI_IRQHandler, Default_Handler)
 // to ensure that it ends up at physical address 0x0000.0000 or at the start of the
 // program if located at a start address other than 0.
 #if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
-void (* const interruptVectors[])(void) __attribute__((section("RESET"))) = {
+void (* const interruptVectors[])(void) __attribute__((section("RESET"), used)) = {
     (pFunc) &Image$$ARM_LIB_STACK$$ZI$$Limit,  // The initial stack pointer
 #elif defined(__ICCARM__)
 void (* const __vector_table[])(void) @ ".intvec" = {
diff --git a/tools/profiles/extensions/lto.json b/tools/profiles/extensions/lto.json
new file mode 100644
index 0000000000..59366afb32
--- /dev/null
+++ b/tools/profiles/extensions/lto.json
@@ -0,0 +1,6 @@
+{
+    "ARMC6": {
+        "common": ["-flto"],
+        "ld": ["--lto", "--lto_level=Oz"]
+    }
+}