Provide atomic read/modify/write support for Cortex M0 [260624583]

Assigned

Bug

Status Update

No update yet.

Description

to...@google.com

created issue #1

Nov 28, 2022 10:29PM

pico_executable doesn't build //pw_intrusive_ptr:intrusive_ptr_test

Disabled this for now in https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/121390

[52/1131] ld rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf
FAILED: rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf.map
arm-none-eabi-g++ -mabi=aapcs -mthumb --sysroot=../environment/cipd/packages/arm -specs=nano.specs -specs=nosys.specs -lnosys -lc -mcpu=cortex-m0plus -mfloat-abi=soft -Os -fdiagnostics-color -Wl,--gc-sections -Wl,--wrap=printf -Wl,--wrap=vprintf -Wl,--wrap=puts -Wl,--wrap=putchar -Wl,--wrap=getchar -T../environment/packages/pico_sdk/src/rp2_common/pico_standard_link/memmap_default.ld -Wl,-Map,rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf.map @rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf.rsp -o rp2040/obj/pw_intrusive_ptr/test/intrusive_ptr_test.elf
/mnt/sdb/pigweed/pigweed/environment/cipd/packages/arm/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: rp2040/obj/pw_intrusive_ptr/pw_intrusive_ptr.ref_counted_base.cc.o: in function `std::__atomic_base<long>::fetch_add(long, std::memory_order)':
out/environment/cipd/packages/arm/arm-none-eabi/include/c++/10.3.1/bits/atomic_base.h:548: undefined reference to `__atomic_fetch_add_4'
/mnt/sdb/pigweed/pigweed/environment/cipd/packages/arm/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: rp2040/obj/pw_intrusive_ptr/pw_intrusive_ptr.ref_counted_base.cc.o: in function `std::__atomic_base<long>::fetch_sub(long, std::memory_order)':
out/environment/cipd/packages/arm/arm-none-eabi/include/c++/10.3.1/bits/atomic_base.h:558: undefined reference to `__atomic_fetch_sub_4'
collect2: error: ld returned 1 exit status

Comments

bl...@google.com <bl...@google.com> #2Nov 28, 2022 10:42PM

Assigned to am...@google.com.

Automated by Blunderbuss job pigweed-blunderbuss-autoassigner for component 1194524.

ca...@google.com <ca...@google.com> #3Jan 26, 2024 11:37PM

http://pwrev.dev/c/189074 ran to similar issues where compare_exchange and exchange functions from std::atomic were not found when linking. One trick was to force alignment to skip the libcalls using pw_alignment, as done in patch 10 (http://pwrev.dev/c/189074/10) and applying this fix: http://pwrev.dev/c/189360. However, the libcalls were still added and the missing reference errors happened again. This could also be due to how the atomic value is accessed in http://pwrev.dev/c/189074/10.

ap...@google.com <ap...@google.com> #4Feb 15, 2024 11:38PM

Project: pigweed/pigweed
Branch: main

commit bb1870ce1c8d99afe0fdf87212a0f19337572ee9
Author: Armando Montanez <amontanez@google.com>
Date: Thu Feb 15 23:37:38 2024

many: Disable tests incompatible with rp2040

Skips tests that are incompatible with the rp2040 when building for that
target.

Bug:

b/260624583

Change-Id: Ic26f657888dc36f241cab43fdd26c1600bd55030
Reviewed-on:

https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/192764
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Erik Gilling <konkers@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>

M pw_allocator/BUILD.gn
M pw_blob_store/BUILD.gn
M pw_chrono/BUILD.gn
M pw_file/BUILD.gn
M pw_fuzzer/examples/fuzztest/BUILD.gn
M pw_i2c/BUILD.gn
M pw_log_rpc/BUILD.gn
M pw_metric/BUILD.gn
M pw_multibuf/BUILD.gn
M pw_protobuf/BUILD.gn
M pw_rpc/nanopb/BUILD.gn
M pw_rpc/pwpb/BUILD.gn
M pw_rpc/raw/BUILD.gn
M pw_rpc_transport/BUILD.gn
M pw_sync/BUILD.gn
M pw_thread/BUILD.gn
M pw_thread_freertos/BUILD.gn
M pw_trace_tokenized/BUILD.gn
M pw_unit_test/BUILD.gn
M third_party/fuchsia/BUILD.gn

https://pigweed-review.git.corp.google.com/192764

tp...@google.com <tp...@google.com> #5Jun 4, 2024 03:45PM

Given our focus on Pico as a platform, should the priority of this be increased? My reading is that this isn't just a narrow issue with the test, but that pw_intrusive_ptr doesn't work with the Pico.

Message last modified on Jun 4, 2024 04:29PM

he...@google.com <he...@google.com> #6Jun 4, 2024 04:34PM

The issue isn't specific to pw_intrusive_ptr. Cortex M0/M0+ does not support atomic read/modify/write, so anything that uses std::atomic types will not compile for Cortex M0.

We could provide implementations of __atomic_fetch_add_4 and related functions. Easy thing to do is disable interrupts (example). As far as I know, that wouldn't work between cores if you're trying to do SMP though.

jr...@google.com <jr...@google.com> #7Mar 17, 2025 06:11PM

Related: b/402489948

he...@google.com <he...@google.com> #8Mar 17, 2025 06:27PM

For Cortex M0 specifically, support for the necessary functions landed in http://pwrev.dev/239719.

Perhaps we can revert http://pwrev.dev/192764?