cpu/esp32: fix heap definition for ESP32-S2 and ESP32-S3

[gschorcht]

Contribution description

For ESP32-S2 and ESP32-S3 the symbol _heap_end must not be used as _eheap for the newlibc malloc and function sbrk.

_heap_end is used by the ESP-IDF heap implementation esp-idf-heap and points to the highest possible address (0x40000000) that could be used for the heap in ESP-IDF. It doesn't point to the top address of the unused SRAM area that can be used in newlibc malloc and function sbrk. Instead, the origin and the length of dram0_0_seg must be used to calculate the end of the heap _eheap.

The problem only occurs for the newlibc malloc when the sbrk function is used but not for the ESP-IDF heap implementation esp_idf_heap.

Testing procedure

Use any ESP32-S2 or ESP32-S3 board and flash tests/sys/malloc, e.g.

CFLAGS='-DCHUNK_SIZE=16384' USEMODULE='stdio_uart' BOARD=esp32s3-pros3 make -j8 -C tests/sys/malloc flash

Without the PR the nm command will give the wrong address

nm -s tests/sys/malloc/bin/esp32s3-pros3/tests_malloc.elf | grep _eheap
40000000 A _eheap

The test will stuck, i.e. the allocation of memory stops when the top of unused SRAM is reached and the board restarts when the watchdog timer expires. With the PR it should work as expected

Help: Press s to start test, r to print it is ready
START
main(): This is RIOT! (Version: 2023.10-devel-309-g4669e)
calloc(zu, zu) = 0x10000000
CHUNK_SIZE: 16384
NUMBER_OF_TESTS: 3
Allocated 16384 Bytes at 0x3fc8c4b0, total 16384
...
Allocated 16384 Bytes at 0x3fcec6f0, total 409792
ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x7 (TG0WDT_SYS_RST),boot:0x8 (SPI_FAST_FLASH_BOOT)
Saved PC:0x403763e3

With this PR the nm command should give a address in unused SRAM address space

nm -s tests/sys/malloc/bin/esp32s3-pros3/tests_malloc.elf | grep _eheap
3fcca000 A _eheap

and the test should pass.

Issues/PRs references

[riot-ci]

Murdock results

✔️ PASSED

3a40e20 cpu/esp32: fix ld scripts for heap

Success	Failures	Total	Runtime
7936	0	7937	14m:26s

Artifacts

• Documentation preview

[benpicco]

bors merge

[bors]

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• Murdock
• static-tests
• tools-build-success