Fix build-SITL-Mac VLA-folding-constant error in log.c (9.1 backport)

[sensei-hacker]

Summary

Backport of #11679 to release/9.1. Fixes the same -Wgnu-folding-constant AppleClang build failure in src/main/common/log.c (_logBufferHex()), which exists identically on this branch.

Root Cause

_logBufferHex() sizes a stack buffer with:

const size_t charsPerByte = 5;
const size_t maxBytes = 8;
char buf[LOG_PREFIX_FORMATTED_SIZE + charsPerByte * maxBytes + 1];

In C (unlike C++), a const-qualified object is not an integer constant expression, so this array size is technically a variable-length array. AppleClang on the macOS CI runner now warns (and -Werror promotes to error) when relying on the GNU extension that folds it back to a fixed size.

Fix

Replace the two const size_t locals with a local enum:

enum {
    charsPerByte = 5,
    maxBytes = 8,
};

Enum constants are genuine integer constant expressions in C (C11 6.6p6), so this is a real fix rather than a suppression. No behavior change: buffer size is 13 + 5*8 + 1 = 54 bytes both before and after.

Testing

• Clean cherry-pick of the already-reviewed maintenance-10.x fix (Fix build-SITL-Mac VLA-folding-constant error in log.c #11679) onto release/9.1 — identical diff, no conflicts.
• Full clean SITL build (Linux/GCC) succeeds with no warnings or errors in log.c.
• build-SITL-Mac CI leg on this PR will provide the authoritative confirmation against the actual AppleClang toolchain.
• No log output formatting change.

Code Review

Same fix already reviewed with inav-code-review agent on #11679 — no critical or important issues found. Approved.

Companion PR (maintenance-10.x): #11679

[qodo-code-review]

PR Summary by Qodo

Fix AppleClang VLA folding warning in log.c (9.1 backport)

🐞 Bug fix 🕐 Less than 10 minutes

AI Description

• Fix AppleClang -Wgnu-folding-constant build failure in _logBufferHex().
• Replace const size_t locals with enum constants for true compile-time sizing.
• Keep buffer size and log formatting behavior unchanged.

Diagram

graph TD
  A["build-SITL-Mac (AppleClang)"] --> B["Compile C sources"] --> C["src/main/common/log.c"] --> D["_logBufferHex()"] --> E["buf[] sized via enum"]

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High-Level Assessment

The following are alternative approaches to this PR:

1. Use preprocessor macros for constants

• ➕ Guaranteed compile-time constants in C
• ➕ Can be reused across functions/files if needed
• ➖ Pollutes global namespace
• ➖ Less scoped/typed than a local enum

2. Hardcode the final buffer size (e.g., 54)

• ➕ Simplest possible compile-time array bound
• ➕ No reliance on constant-expression rules
• ➖ Less self-documenting; intent (5 chars/byte, 8 bytes) is obscured
• ➖ More error-prone if formatting rules change

3. Move constants to file-scope enum/static constants

• ➕ Still compile-time constant if enum at file scope
• ➕ Avoids repeating constants in multiple functions
• ➖ Wider scope than necessary for values used only in one function
• ➖ Static const at file scope still isn’t an ICE in C for array bounds

Recommendation: Keep the PR’s local enum approach: it is the most correct C fix (true integer constant expressions) while staying narrowly scoped and preserving readability and behavior. Macros and hardcoded sizes are viable but either broaden scope or reduce clarity.

Files changed (1) +6 / -2

Bug fix (1) +6 / -2

log.cMake _logBufferHex() stack buffer size a true constant expression +6/-2

Make _logBufferHex() stack buffer size a true constant expression

• Replaces two 'const size_t' locals used in an array bound with a local 'enum' so AppleClang no longer treats the buffer as a VLA under -Wgnu-folding-constant. Adds a clarifying comment and preserves the exact buffer sizing and output behavior.

src/main/common/log.c

[qodo-code-review]

Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

Great, no issues found!

Qodo reviewed your code and found no material issues that require review

[github-actions]

Test firmware build ready — commit b757e48

Download firmware for PR #11680

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