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Request for comments: Expand sbrk to allocate memory from two regions #9441

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Request for comments: Expand sbrk to allocate memory from two regions #9441

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10 changes: 7 additions & 3 deletions targets/TARGET_STM/TARGET_STM32L4/TARGET_STM32L475xG/device/TOOLCHAIN_GCC_ARM/STM32L475XX.ld
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ M_CRASH_DATA_RAM_SIZE = 0x100;

/* Linker script to configure memory regions. */
MEMORY
{
{
FLASH (rx) : ORIGIN = MBED_APP_START, LENGTH = MBED_APP_SIZE
SRAM2 (rwx) : ORIGIN = 0x10000188, LENGTH = 32k - 0x188
SRAM1 (rwx) : ORIGIN = 0x20000000, LENGTH = 96k
Expand All @@ -26,7 +26,7 @@ MEMORY
* with other linker script that defines memory regions FLASH and RAM.
* It references following symbols, which must be defined in code:
* Reset_Handler : Entry of reset handler
*
*
* It defines following symbols, which code can use without definition:
* __exidx_start
* __exidx_end
Expand Down Expand Up @@ -93,7 +93,7 @@ SECTIONS

__etext = .;
_sidata = .;

.crash_data_ram :
{
. = ALIGN(8);
Expand Down Expand Up @@ -173,6 +173,10 @@ SECTIONS
.stack_dummy (COPY):
{
*(.stack*)
. += (ORIGIN(SRAM2) + STACK_SIZE - .);
__mbed_sbrk_start_0 = .;
. += (ORIGIN(SRAM2) + LENGTH(SRAM2) - .);
__mbed_krbs_start_0 = .;
} > SRAM2

/* Set stack top to end of RAM, and stack limit move down by
Expand Down
24 changes: 19 additions & 5 deletions targets/TARGET_STM/TARGET_STM32L4/l4_retarget.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,25 +33,39 @@
******************************************************************************
*/
#if (defined(TWO_RAM_REGIONS) && defined(__GNUC__) && !defined(__CC_ARM) && !defined(__ARMCC_VERSION))
#include <stdbool.h>
#include <errno.h>
#include "stm32l4xx.h"
extern uint32_t __mbed_sbrk_start;
extern uint32_t __mbed_krbs_start;
extern uint32_t __mbed_sbrk_start_0;
extern uint32_t __mbed_krbs_start_0;

/**
* The default implementation of _sbrk() (in platform/mbed_retarget.cpp) for GCC_ARM requires one-region model (heap and
* stack share one region), which doesn't fit two-region model (heap and stack are two distinct regions), for example,
* STM32L475xG locates heap on SRAM1 and stack on SRAM2.
* The default implementation of _sbrk() (in platform/mbed_retarget.cpp) for GCC_ARM only supports one region.
* This implementation supports two regions by continuing the allocation to the second region after the first
* one is full.
* Define __wrap__sbrk() to override the default _sbrk(). It is expected to get called through gcc
* hooking mechanism ('-Wl,--wrap,_sbrk') or in _sbrk().
*/
void *__wrap__sbrk(int incr)
{
static uint32_t heap_ind = (uint32_t) &__mbed_sbrk_start;
static uint32_t heap_ind = (uint32_t) &__mbed_sbrk_start_0;
static bool once = true;
uint32_t heap_ind_old = heap_ind;
uint32_t heap_ind_new = heap_ind_old + incr;

if (heap_ind_new > (uint32_t)&__mbed_krbs_start) {
/**
* If the new address is outside the first region, start allocating from the second region.
*/
if (once && (heap_ind_new >= (uint32_t)&__mbed_krbs_start_0)) {
once = false;
heap_ind_old = (uint32_t)&__mbed_sbrk_start;
heap_ind_new = heap_ind_old + incr;
/**
* If the new address is outside the second region, return out-of-memory.
*/
} else if (heap_ind_new >= (uint32_t)&__mbed_krbs_start) {
errno = ENOMEM;
return (void *) - 1;
}
Expand Down