uBPF should build /w4 /wx clean (i.e. no level 4 warnings).

[Alan-Jowett]

[Alan-Jowett]

Feature Specification: Enable /W4 /WX (Warnings as Errors) on Windows

Problem Statement

The uBPF build currently has inconsistent warning treatment across platforms:

Platform	Warning Level	Warnings as Errors
Linux/macOS	-Wall	-Werror ✅
Windows	/W4	Missing ❌

Current Windows config (cmake/settings.cmake:92-94):

target_compile_options("ubpf_settings" INTERFACE
  /W4
)

Missing: /WX to treat warnings as errors, equivalent to -Werror.

---

Goals

1. Add /WX to Windows builds to match Linux/macOS strictness
2. Fix all existing level 4 warnings in the codebase
3. Ensure CI catches new warnings on all platforms

---

Common Level 4 Warnings to Fix

Based on typical MSVC /W4 warnings in C code:

Warning	Description	Typical Fix
C4100	Unreferenced formal parameter	UNUSED_PARAMETER(x) macro
C4127	Conditional expression is constant	Refactor or #pragma warning(disable)
C4201	Nameless struct/union	Add names or disable
C4244	Conversion with possible data loss	Explicit cast
C4245	Signed/unsigned mismatch	Explicit cast
C4267	Size_t to smaller type	Explicit cast
C4389	Signed/unsigned comparison	Fix types
C4706	Assignment within conditional	Use if ((x = y) != 0)

---

Implementation Plan

Phase 1: Audit Current Warnings

# Build with /W4 and capture warnings
cmake -S . -B build
cmake --build build 2>&1 | Select-String "warning C"

Phase 2: Fix Warnings

Categorize and fix each warning type:

1. Unused parameters - Add UNUSED_PARAMETER() or (void)param;
2. Type conversions - Add explicit casts with comments
3. Intentional patterns - Add targeted #pragma warning(disable:XXXX)

Phase 3: Enable /WX

File: cmake/settings.cmake line 92-94:

target_compile_options("ubpf_settings" INTERFACE
  /W4
  /WX    # Treat warnings as errors
)

---

Handling Unavoidable Warnings

For warnings that can't be fixed (e.g., external headers, intentional patterns):

// Option 1: Targeted pragma (preferred)
#pragma warning(push)
#pragma warning(disable:4201)  // nameless struct/union
#include <some_header.h>
#pragma warning(pop)

// Option 2: Macro wrapper
#ifdef _MSC_VER
#define UBPF_SUPPRESS_WARNING_BEGIN(num) __pragma(warning(push)) __pragma(warning(disable:num))
#define UBPF_SUPPRESS_WARNING_END __pragma(warning(pop))
#else
#define UBPF_SUPPRESS_WARNING_BEGIN(num)
#define UBPF_SUPPRESS_WARNING_END
#endif

---

Files Likely to Need Changes

File	Expected Issues
vm/ubpf_vm.c	Unused params, type conversions
vm/ubpf_jit_x86_64.c	Size conversions, casts
vm/ubpf_loader.c	Signed/unsigned comparisons
vm/ubpf_jit_arm64.c	Similar to x86_64

---

Acceptance Criteria

• /WX added to Windows build settings
• All /W4 warnings fixed or explicitly suppressed
• Windows CI builds pass with no warnings
• Linux/macOS builds still pass (no regressions)
• Code review ensures fixes don't introduce bugs
• Suppressed warnings documented with rationale

---

CI Verification

The Windows CI workflow already builds with the settings from cmake/settings.cmake. Once /WX is added, any new warnings will fail the build.

---

Test Plan

# Local verification on Windows
cmake -S . -B build -DUBPF_ENABLE_TESTS=true
cmake --build build --config Release 2>&1 | Tee-Object build.log

# Check for any warnings
Select-String "warning" build.log
# Should return empty after fixes

---

References

• Current settings: cmake/settings.cmake:89-103
• MSVC Warning levels: https://docs.microsoft.com/en-us/cpp/build/reference/compiler-option-warning-level
• Linux equivalent: -Wall -Werror at line 17-18