Inconsistent heap sizes between toolchains, especially IAR

[kuggenhoffen]

Description

• Type: Bug
• Priority: Major

---

Bug

Target
K64F

Toolchain:
IAR

Toolchain version:
7.80.2.11975

mbed-cli version:
1.0.0

meed-os sha:
a1c0840 (HEAD, tag: mbed_lib_rev129, tag: mbed-os-5.2.2) Merge pull request #3227 from ARMmbed/release-candidate

Expected behavior
I would expect available heap amount to be somewhat similar between all the toolchains to guarantee compatibility. Currently it seems that the available heap is very different in IAR (~65k) compared to ARMCC (~180k) or GCC (~175k)

Actual behavior
IAR heap size seems to be fixed at ~65k

Steps to reproduce
Numbers above were determined with following code on K64F with serial terminal:

#include "mbed.h"

RawSerial   pc(USBTX, USBRX);

static void heap_loop_check(int maxSize, int total)
{
    pc.printf("Next try: %d, total so far: %d\r\n", maxSize, total);
    for(int n = maxSize; n >= 0; n--){
        if(n == 0){
            pc.printf("Available heap: %d\r\n", total);
            break;
        }
        void *block;
        block = malloc(n);
        if (!block) {
          continue;
        }
        heap_loop_check(n, total + n);
        free(block);
        break;
    }
}

int main() {
    pc.baud(115200);
    heap_loop_check(80000, 0);
}

[0xc0170]

@c1728p9 Didn't we unified the heap sizes? I can't find the patch.

As I recall it used to be that IAR requires a fixed heap size, and the rest toolchains are flexible (allowing heap to grow).

[c1728p9]

With ARM and GCC_ARM the heap takes up all remaining free RAM space. The IAR heap is a fixed, hardcoded size due to toolchain limitations.

[kuggenhoffen]

How do I increase heap size for application? I can modify the linker file but is there a compatible way that will work for all targets and toolchains as well as is somehow portable for an application?

[kuggenhoffen]

Also GCC reports allocated heap as 65k when it actually allocated over 100k more, which is a bit misleading.

[0xc0170]

How do I increase heap size for application? I can modify the linker file but is there a compatible way that will work for all targets and toolchains as well as is somehow portable for an application?

Currently not, defined in the linker script per toolchain (IAR has it predefined, others remaining space used).

@c1728p9 Is this documented anywhere? We might consider having it in the Handbook

[c1728p9]

I think the only info we have on this is here:
https://github.com/ARMmbed/Handbook/blob/master/docs/concepts/memory_model.md

Ideally we would get IAR to match everything else so these problems wouldn't occur in the first place.

[yogpan01]

@c1728p9 @0xc0170 any updates on this ? Do we have a solution for fixed Heap problem for IAR ?

[c1728p9]

Last I heard, IAR had no intention of making their allocator dynamically sizable. @sg- have you heard anything new from them?

GitHib issue review: Closed due to inactivity. Please re-file if critical issues found.