When using the default gcc linker script and adding the option `-Wl,--print-memory`, the RAM usage always displays as 100%

[mikisama]

The RAM usage always displays as 100% when I using the default gcc linker script

CMSIS_6/CMSIS/Core/Template/Device_M/Config/Device_gcc.ld

Line 294 in fdbbc52

.stack (ORIGIN(RAM) + LENGTH(RAM) - __STACK_SIZE - __STACKSEAL_SIZE) (NOLOAD) :

Memory region         Used Size  Region Size  %age Used
           FLASH:       17272 B        48 KB     35.14%
             RAM:        4080 B       4080 B    100.00%

I fix this by change the linkscript to

  .stack (NOLOAD) :

Memory region         Used Size  Region Size  %age Used
           FLASH:       17272 B        48 KB     35.14%
             RAM:        1640 B       4080 B     40.20%

[JonatanAntoni]

Hi @mikisama,

While you can change that freely based on your project needs, the downside of removing the placement constraint is not keeping the C stack at the very end of the RAM region. By default, we want a memory layout like:

---- RAM ---
static memory
heap
 ⬇
 ︙
 ⬆
stack
------------

I.e., heap grows into increasing addresses while stack grows towards decreasing addresses.
You're proposal puts the stack directly after the reserved heap:

---- RAM ---
static memory
heap
 ⬇
 ⬆
stack
 ︙
------------

Which leads to stack overflows directly writing into reserved heap memory.

As this proposal does not change anything functional wise, I'd tend to blame the compilers/linkers RAM usage calculation to be off.

[mikisama]

Hi, @JonatanAntoni

Thanks for you reply and I got you point.

For gnu ldscript, is there a way to place the stack at the end of RAM and ensure that the RAM usage report generated using the -Wl,--print-memory option is correct?

[JonatanAntoni]

@mikisama, after a quick check with some compiler experts I doubt there is a way. But you could try to jump into a discussion with the GNU compiler channels.