Firebase/React Native iOS Build Issue: Abseil Undefined Symbols, React Native0.76.5, Firebase and Xcode26.2

[dimturkee-lab]

Description

Building a React Native iOS app with Firebase Firestore results in 50+ undefined symbol errors for absl::lts_20240722::* functions. The symbols exist in the abseil library (verified with nm), but are not being resolved by the linker despite using -force_load.

Critical Finding: Symbols ARE present in the archive, but -force_load is not loading all archive members. Some abseil symbols ARE resolved (e.g., Mutex::Mutex()), but many others are not (e.g., CHexEscape, FormatTime, SimpleAtod, etc.).

Environment History

React Native Versions Tested

• Started with: React Native 0.74.5 (original issue)
• Upgraded to: React Native 0.76.5 (issue persists)
• Rationale for upgrade: Attempted to resolve compatibility issues, but did not fix the abseil linking problem

Xcode Versions Tested

• Xcode 26.2 (Build 17C52) - Issue present
• Xcode 16.4 - Issue persists, additionally had glog build problems
• Current: Xcode 26.2

Current Environment

• React Native: 0.76.5
• Firebase iOS SDK: 12.6.0
• abseil: 1.20240722.0
• CocoaPods: 1.16.2 (also tried 1.15.2 - same results)
• xcodeproj gem: 1.27.0
• Platform: iOS Simulator (arm64)
• Linkage Mode: Static libraries (not frameworks)

Error Messages

Undefined symbols for architecture arm64:
  "absl::lts_20240722::CHexEscape(std::__1::basic_string_view<char, std::__1::char_traits<char>>)"
  "absl::lts_20240722::FormatTime(std::__1::basic_string_view<char, std::__1::char_traits<char>>, absl::lts_20240722::Time, absl::lts_20240722::TimeZone)"
  "absl::lts_20240722::SimpleAtod(std::__1::basic_string_view<char, std::__1::char_traits<char>>, double*)"
  "absl::lts_20240722::SimpleAtof(std::__1::basic_string_view<char, std::__1::char_traits<char>>, float*)"
  "absl::lts_20240722::Base64Escape(...)"
  ... (50+ more similar errors)

Verification: Symbols Exist in Archive ✅

Confirmed with nm command:

nm libabseil.a | grep CHexEscape
# Output: 0000000000000684 T __ZN4absl12lts_20240722CHexEscapeENS0_11string_viewE

nm libabseil.a | grep FormatTime  
# Output: 0000000000000000 T __ZN4absl12lts_2024072210FormatTimeENS0_11string_viewENS0_4TimeENS0_8TimeZoneE

Archive Details:

• Archive exists at: ${PODS_CONFIGURATION_BUILD_DIR}/abseil/libabseil.a
• Architecture: Universal binary (arm64 + x86_64) ✅
• Symbols present: Verified with nm ✅
• Some symbols DO resolve: Mutex::Mutex(), Notification::WaitForNotification() ✅
• Many symbols DO NOT resolve: CHexEscape, FormatTime, SimpleAtod, etc. ❌

Linker Command Observation:

• -Wl,-force_load,${PODS_CONFIGURATION_BUILD_DIR}/abseil/libabseil.a is present ✅
• Flag is positioned BEFORE $(inherited) ✅
• Archive path resolves correctly ✅
• BUT: Symbols still not resolved ❌

Comprehensive List of Attempted Fixes

1. Firebase Recommended Workaround ✅ Applied

• Action: Set CLANG_CXX_LANGUAGE_STANDARD = 'gnu++14' for abseil target
• Location: Applied at the very end of Podfile post_install hook
• Result: ❌ Did not resolve the issue
• Verification: Confirmed workaround is applied (shown in pod install output)

2. CocoaPods Version Changes ✅ Tested

• Versions tried: CocoaPods 1.16.2 (latest) and 1.15.2 (older)
• Result: ❌ Both versions produce identical errors
• xcodeproj gem: 1.27.0 (required for CocoaPods 1.16+)

3. Xcode Version Changes ✅ Tested

• Xcode 26.2: Issue present
• Xcode 16.4: Same errors, plus glog build issues
• Result: ❌ Xcode version is not the root cause

4. React Native Version Upgrade ✅ Tested

• Started: React Native 0.74.5
• Upgraded to: React Native 0.76.5 (hoping to fix compatibility issues)
• Result: ❌ Issue persists on both versions

5. Linker Flag Approaches ✅ Multiple Attempts

A. Added -force_load to intermediate targets

• Action: Added -Wl,-force_load for abseil to gRPC-Core, FirebaseFirestoreInternal, gRPC-C++ targets
• Result: ❌ Symbols still undefined

B. Added -force_load to main app target

• Action: Added -Wl,-force_load,${PODS_CONFIGURATION_BUILD_DIR}/abseil/libabseil.a to ResponderMapNew target's OTHER_LDFLAGS
• Position: BEFORE $(inherited) to ensure early processing
• Result: ❌ Symbols still undefined

C. Tried -all_load flag

• Action: Attempted -Wl,-all_load instead of -force_load
• Result: ❌ Same errors, also causes issues with other libraries

D. Verified flag position in linker command

• Action: Confirmed -force_load appears before other libraries in actual linker command
• Result: ✅ Flag is correctly positioned, but still not working

6. Abseil Build Configuration ✅ Applied

All of the following settings are applied to the abseil target in Podfile post_install:

config.build_settings['MACH_O_TYPE'] = 'staticlib'
config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
config.build_settings['GCC_GENERATE_DEBUGGING_SYMBOLS'] = 'YES'
config.build_settings['SKIP_INSTALL'] = 'NO'
config.build_settings['ARCHS'] = 'arm64 x86_64'
config.build_settings['DEAD_CODE_STRIPPING'] = 'NO'
config.build_settings['SYMBOLS_HIDDEN_BY_DEFAULT'] = 'NO'
config.build_settings['CLANG_CXX_LANGUAGE_STANDARD'] = 'gnu++14'  # Firebase workaround

• Result: ❌ Issue persists with all these settings

7. Target Dependencies ✅ Applied

• Action: Added abseil as explicit target dependency for ResponderMapNew
• Result: ❌ Does not resolve the linking issue

8. Clean Builds ✅ Performed Multiple Times

• Actions:
  • Cleaned DerivedData multiple times
  • Removed Pods directory and reinstalled
  • Clean Build Folder in Xcode
  • Rebuilt from scratch
• Result: ❌ Issue persists after every clean build

9. Module Map Fixes ✅ Applied

• Action: Fixed gRPC-Core.modulemap path issues (common Firebase/React Native issue)
• Location: Created modulemap and added pre-compile script
• Result: ✅ Module map issues resolved, but abseil linking issue persists

10. React Native Upgrade Related Fixes ✅ Applied

• Action: Applied fixes for React Native 0.76.5:
  • Global use_modular_headers! for Firebase Swift pods
  • gRPC-Core.modulemap creation and pre-compile script
  • Fixed react-native-maps EventEmitterCallbackWrapper access (separate issue)
• Result: ✅ These fixes applied successfully, but abseil linking issue persists

Current Podfile Configuration

Key post_install Hook Sections:

1. Abseil Build Settings:

   • Forces static library build
   • Disables dead code stripping
   • Disables symbol hiding
   • Sets C++ standard to gnu++14
   • Builds universal binary

2. Force Load Flag:

   abseil_force_load_flag = '-Wl,-force_load,${PODS_CONFIGURATION_BUILD_DIR}/abseil/libabseil.a'
   # Prepend BEFORE $(inherited) in OTHER_LDFLAGS

3. Target Dependencies:

   • Explicitly adds abseil as dependency for ResponderMapNew target

Critical Observations

1. Partial Linking Success:

   • Some abseil symbols ARE resolved (e.g., Mutex::Mutex() found in libabseil.a[arm64][82](mutex.o))
   • Many abseil symbols are NOT resolved (e.g., CHexEscape, FormatTime)
   • This suggests the archive IS being processed, but not all members are loaded

2. Symbol Verification:

   • Verified with nm that missing symbols exist in the archive
   • Archive is a valid universal binary with both architectures
   • Archive path is correct and accessible

3. Linker Behavior:

   • -force_load flag is present and correctly positioned
   • Linker processes the archive (some symbols work)
   • But -force_load is not forcing ALL archive members to load

4. Consistency Across Versions:

   • Issue persists across React Native 0.74.5 and 0.76.5
   • Issue persists across Xcode 26.2 and 16.4
   • Standard linking fixes have no effect

Hypothesis

The issue appears to be that -force_load is not functioning as expected for the abseil static library. Possible causes:

1. Linker Bug: There may be a bug in the linker (ld) that prevents -force_load from loading all archive members for this specific library
2. Archive Structure: The abseil archive might have a structure that prevents -force_load from working correctly
3. Symbol Visibility: Despite setting SYMBOLS_HIDDEN_BY_DEFAULT = NO, symbols might still have hidden visibility
4. Build Toolchain Issue: Combination of React Native, Firebase, abseil, and Xcode might expose a toolchain bug

Additional Context

• Android Build: Works correctly (not affected by this iOS-specific issue)
• Other Libraries: No linking issues with other Firebase or React Native libraries
• Project Complexity: Standard React Native app with Firebase Firestore, Auth, Functions, Messaging

Request for Help

This issue has persisted through:

• Multiple React Native versions (0.74.5 → 0.76.5)
• Multiple Xcode versions (26.2, 16.4)
• Extensive configuration changes
• All standard troubleshooting approaches

Given that:

1. Symbols exist in the archive (verified)
2. -force_load is correctly configured (verified)
3. Some symbols ARE resolved (proving the archive is processed)
4. Many symbols are NOT resolved (despite being in the archive)

We believe this may be:

• A deeper linker/toolchain issue
• A compatibility problem between React Native, Firebase, abseil, and recent Xcode versions
• A bug that requires upstream fixes

Questions for Firebase/React Native Firebase team:

1. Is this a known issue with React Native 0.74.5+ / 0.76.5 and Firebase?
2. Are there any workarounds beyond the standard gnu++14 setting?
3. Is there a different linking approach we should try?
4. Should we consider downgrading Firebase iOS SDK versions?
5. Are there any pending fixes for abseil linking in upcoming releases?

Files Modified

• ios/Podfile - Extensive post_install hooks for abseil configuration
• ios/Pods/Target Support Files/**/*.xcconfig - Modified to fix module map paths
• node_modules/react-native-maps/ios/generated/RNMapsSpecs/* - Fixed for RN 0.76.5 compatibility

Build Command Output

The linker command includes:

-Wl,-force_load,/path/to/Build/Products/Debug-iphonesimulator/abseil/libabseil.a

Positioned before all other library flags, but symbols still not resolved.

---

Date: December 23, 2024
Status: Issue unresolved after extensive troubleshooting
Next Steps: Awaiting guidance from Firebase/React Native Firebase support

Reproducing the issue

Reproduction Steps

1. Create React Native 0.76.5 project
2. Install Firebase: npm install @react-native-firebase/app @react-native-firebase/firestore
3. Run cd ios && pod install
4. Build in Xcode
5. Observe undefined symbol errors for abseil functions

Firebase SDK Version

12.6.0

Xcode Version

26.2

Installation Method

CocoaPods

Firebase Product(s)

All

Targeted Platforms

iOS, macOS

Relevant Log Output

If using Swift Package Manager, the project's Package.resolved

Expand Package.resolved snippet

Replace this line with the contents of your Package.resolved.

If using CocoaPods, the project's Podfile.lock

Expand Podfile.lock snippet

Replace this line with the contents of your Podfile.lock!

[MarkDuckworth]

Hi @dimturkee-lab, thanks for your post. Due to the proximity to the holiday, we may be delayed in responding. But one of our c++ experts should be able to take a look soon after the holiday.

[dimturkee-lab]

Thank you! Merry Christmas and Happy New Year! Tim

…

On Wed, Dec 24, 2025, 09:48 Mark Duckworth ***@***.***> wrote: *MarkDuckworth* left a comment (firebase/firebase-ios-sdk#15642) <#15642 (comment)> Hi @dimturkee-lab <https://github.com/dimturkee-lab>, thanks for your post. Due to the proximity to the holiday, we may be delayed in responding. But one of our c++ experts should be able to take a look soon after the holiday. — Reply to this email directly, view it on GitHub <#15642 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BZOGY3CNIIOL77T7PE7WE234DLGVJAVCNFSM6AAAAACP5K2HUWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMOJQGMYDKNJUGU> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[cherylEnkidu]

Hi @dimturkee-lab — thanks again for the detailed report.

I’m going to take another look at this early next year, but in the meantime there are a couple of things you could try during the holidays.

So far, we haven’t been able to reproduce the issue. However, we’ve seen very similar error messages internally when updating the SDK to use C++17.

Our current hypothesis is that the language standard defined only applies to that package’s own targets. If one dependency is built with C++17 and another with C++14, there’s no single resolution step — each package ends up being built with its own compiler flags.

In your project, it’s possible that another dependency is pulling in a different version of abseil, which could lead to inconsistent build behavior (even though, in theory, the compiler should handle this more gracefully).

Another observation we’ve made is that the build result can differ depending on whether the SDK is built from source or from a prebuilt dependency. This difference seems to show up when using Swift Package Manager, but not when using CocoaPods. As an experiment, you could try pointing your Podfile to a local clone of the SDK (building from source) to see whether that changes the behavior.

Thanks again for taking the time to put together such a thorough bug report, and happy holidays! 🎄