waf: detect 64-bit Linux targets for DroneCAN

[dlanov]

Summary

Detect the configured Linux target's pointer width and define CANARD_64_BIT explicitly for 64-bit DroneCAN builds.

Fixes #33721.

Classification & Testing

• Checked by a human programmer
• Non-functional change
• No-binary change
• Infrastructure change
• Automated test(s) verify changes
• Tested manually, description below
• Tested on hardware
• Logs attached
• Logs available on request

Description

Libcanard determines whether it is compiling for a 64-bit target using glibc's __WORDSIZE macro. Musl does not provide that macro through the headers included by libcanard, so an AArch64 musl build incorrectly selects the 32-bit libcanard data layout and fails its compile-time structure-layout assertion.

Add a compile-only Waf check that uses the configured target C compiler to determine whether pointers are eight bytes. When the check succeeds, CANARD_64_BIT=1 is added to the common build definitions, including the generated DroneCAN C sources.

The check is limited to Linux boards with CAN enabled and does not rely on the build host architecture or an architecture-name list.

Testing

AArch64 Alpine/musl baseline

Before the change, the static Linux Rover build failed in generated DroneCAN C sources with:

modules/DroneCAN/libcanard/canard.h:371:
static assertion failed: "Invalid memory layout"

AArch64 Alpine/musl after the change

• Checking for 64-bit pointers: yes
• Full Linux Rover build completed successfully
• Generated DroneCAN C compile commands contained CANARD_64_BIT=1
• The result was an ELF 64-bit ARM AArch64 statically linked executable
• The libcanard memory-layout failure was no longer present

ARMHF/musl regression build

Using the existing navigator ARMHF/musl CI-style build:

• Checking for 64-bit pointers: no
• The Sub build completed successfully
• CANARD_64_BIT=1 was absent from compile_commands.json
• The resulting executable was a 32-bit ARM ELF

Additional checks:

• git diff --check
• python3 -m py_compile Tools/ardupilotwaf/boards.py
• Tools/scripts/check_branch_conventions.py
• Confirmed only Tools/ardupilotwaf/boards.py changed

AI Assistance

This contribution was AI-assisted. Claude and ChatGPT were used to analyze the Waf and libcanard behavior, develop the validation plan, and review the proposed change and test results. I reproduced the failure, reviewed the code, ran the listed builds and checks, and take responsibility for the submitted change.

[peterbarker]

LGTM

[khancyr]

I would say OK

But we need to look at the combination of this that auto set 64bit flag and the --force-32bit . We may have some conflict there.

[khancyr]

Ok, I check the flag combination and it works for now as the order is correct. It will break if we change the flag order
adding
if not cfg.options.force_32bit: as guard would make it safer