Introduction

This error means an iOS build is passing the compiler flag -G to an Apple clang toolchain targeting arm64-apple-ios15.0, even though that flag is not valid for that target. The real problem is usually not BoringSSL itself. It is a bad flag leaking into the gRPC or BoringSSL build from outdated build settings, a dependency integration issue, or an incorrectly inherited cross-platform compiler configuration.

Why -G fails on this target

-G is not a normal Apple iOS clang option for arm64 builds. Flags like this often make sense only in other compiler or architecture contexts. When an iOS dependency build sees it, the failure usually means some build configuration was written with the wrong platform assumptions and then reused where it does not belong.

So the useful question is not "what does BoringSSL do with -G?" The useful question is "who injected -G into the iOS compile command?"

Start by finding the source of the flag

Inspect the actual build command or Xcode build log. Search for -G in:

• Xcode build settings
• 'OTHER_CFLAGS'
• podspecs and generated CocoaPods xcconfig files
• custom environment variables in the build pipeline
• third-party scripts that patch compiler flags globally

The goal is to find where the bad flag first appears.

Old dependency integrations are a common cause

This kind of error often shows up when:

• CocoaPods state is stale
• gRPC and BoringSSL versions are mismatched
• a project carries old manually edited xcconfig files
• a cross-platform project injects generic C flags into iOS targets

That is why a clean dependency refresh is often part of the fix.

A typical cleanup sequence looks like this:

rm -rf Pods Podfile.lock
pod repo update
pod install

If the flag came from stale generated pod settings, regenerating the integration can remove it.

Check for globally inherited compiler flags

In larger iOS projects, the bad flag is sometimes not inside BoringSSL or gRPC at all. It may come from a parent project setting that gets inherited by every native dependency target.

In Xcode, inspect target and project build settings for Other C Flags and Other C++ Flags. If -G appears there, removing it from the shared configuration often fixes all affected dependency targets at once.

That is especially common in mixed-platform build systems where iOS inherits flags intended for Linux, embedded, or non-Apple toolchains.

Keep the iOS build path boring

The safest iOS build configuration is usually the least clever one:

• use Apple's toolchain as intended
• let CocoaPods or Swift Package Manager generate dependency settings cleanly
• avoid global compiler-flag overrides unless absolutely necessary

BoringSSL and gRPC are sensitive low-level dependencies. Exotic project-wide compiler mutations tend to surface there first.

Update instead of patching blindly

You can sometimes force the build to continue by manually stripping -G from generated files, but that is usually a short-lived workaround. If the bad flag is generated from upstream config, the next install or build regeneration will reintroduce it.

The durable fix is to remove the source of the flag, not the symptom copy.

Common Pitfalls

• Assuming BoringSSL itself invented the bad flag rather than checking inherited build settings first.
• Editing generated pod files manually without fixing the upstream config that reintroduces the flag.
• Keeping stale CocoaPods or dependency lock state after changing the toolchain or iOS target.
• Applying cross-platform compiler flags globally to Apple iOS targets.
• Treating this as an ARM64 problem alone when the real issue is toolchain-flag mismatch.

Summary

• The error occurs because -G is being passed to an iOS arm64 Apple clang build where it is unsupported.
• The real bug is usually a leaked or inherited compiler flag, not BoringSSL's core logic.
• Search build settings, CocoaPods configs, and generated compile commands for the source of -G.
• Regenerating dependency integration often helps if stale pod configuration is involved.
• Fix the origin of the bad flag instead of patching generated files repeatedly.