I'm using a different configuration and keep running into
`gen/third_party/libc++/src/include/__cstddef/byte.h:13:10: fatal error:
'__fwd/byte.h' file not found`.
```
target_os="android"
target_cpu="arm64"
v8_target_cpu="arm64"
android_ndk_api_level = 27
android_ndk_root = "/v8build/android-ndk-r27d"
android_ndk_version = "r27d"
# false = use ndk's libc++, true (default) = use custom bundled version
use_custom_libcxx = false
# this will tell compiler to use custom bundled libcc for compiling
#use_custom_libcxx_for_host = true
is_component_build=false
v8_monolithic=true
v8_static_library=true
is_clang = true
clang_use_chrome_plugins=false
dcheck_always_on = false
icu_use_data_file = false
is_debug = false
strip_debug_info=true
symbol_level=0
v8_symbol_level=0
use_libfuzzer=false
v8_android_log_stdout = true
v8_enable_handle_zapping=false
v8_enable_i18n_support=true
v8_enable_pointer_compression=false
v8_enable_test_features=false
v8_enable_webassembly=false
v8_use_external_startup_data=false
```
```
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MD -MF
obj/build/modules/android-arm64/std_core/module.pcm.d -D_GNU_SOURCE
-D__ARM_NEON__=1 -DANDROID -D__ANDROID_UNAVAILABLE_SYMBOLS_ARE_WEAK__
-DHAVE_SYS_UIO_H -DANDROID_NDK_VERSION_ROLL=r27d_1
-DCR_CLANG_REVISION=\"llvmorg-22-init-8940-g4d4cb757-84\"
-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_NONE -DNDEBUG -DNVALGRIND
-DDYNAMIC_ANNOTATIONS_ENABLED=0 -D_LIBCPP_BUILDING_LIBRARY -I../.. -Igen
-fno-implicit-module-maps -fno-delete-null-pointer-checks
-fno-strict-overflow -fno-ident -fno-math-errno -fno-strict-aliasing
-fstack-protector -funwind-tables -fPIC -fcolor-diagnostics
-fmerge-all-constants -fno-sized-deallocation
-fcrash-diagnostics-dir=../../out/clang-crashreports -mllvm
-instcombine-lower-dbg-declare=0 -mllvm
-split-threshold-for-reg-with-hint=0 -ffp-contract=off -ffunction-sections
-fno-short-enums -mbranch-protection=standard
--target=aarch64-linux-android27 -mno-outline -Wno-builtin-macro-redefined
-D__DATE__= -D__TIME__= -D__TIMESTAMP__= -ffile-compilation-dir=.
-no-canonical-prefixes -Xclang -fmodule-file-home-is-cwd -Xclang
-fmodules-cache-path=/not_exist_dummy_dir -ftrivial-auto-var-init=pattern
-O2 -fdata-sections -ffunction-sections -fno-unique-section-names
-fno-omit-frame-pointer -g0 -fsanitize=array-bounds
-fsanitize-trap=array-bounds -fvisibility=hidden -Wheader-hygiene
-Wstring-conversion -Wtautological-overlap-compare -fstrict-aliasing
-Wundef -fPIC -Wall -Wno-unused-variable -Wno-c++11-narrowing
-Wno-unused-but-set-variable -Wunguarded-availability
-Wno-missing-field-initializers -Wno-unused-parameter -Wno-psabi
-Wloop-analysis -Wno-unneeded-internal-declaration -Wno-cast-function-type
-Wno-thread-safety-reference-return -Wno-nontrivial-memcall
-Wno-uninitialized-const-pointer -Werror -Wno-exit-time-destructors
-std=c++20 -Wno-trigraphs -gsimple-template-names -fno-exceptions -fno-rtti
--sysroot=../../../android-ndk-r27d/toolchains/llvm/prebuilt/linux-x86_64/sysroot
-fvisibility-inlines-hidden -fbuiltin-module-map
-fmodule-map-file=gen/third_party/libc++/src/include/module.modulemap
-fmodule-map-file=gen/build/modules/android-arm64/module.modulemap
-Wno-invalid-offsetof -Wenum-compare-conditional
-Wno-nullability-completeness
-fmodule-map-file=gen/third_party/libc++/src/include/module.modulemap
-fbuiltin-module-map
-fmodule-map-file=gen/build/modules/android-arm64/module.modulemap
-fmodule-file=obj/build/modules/android-arm64/_Builtin_stddef/module.pcm
-fmodule-file=obj/build/modules/android-arm64/_Builtin_stdint/module.pcm
-fmodule-file=obj/build/modules/android-arm64/sys_stage1/module.pcm
-fmodule-name=std_core -x c++ -Xclang -emit-module -c
gen/third_party/libc++/src/include/module.modulemap -o
obj/build/modules/android-arm64/std_core/module.pcm
build step: cxx_module
"./obj/build/modules/android-arm64/std_core/module.pcm"
siso_rule: clang/cxx_module
stderr:
While building module 'std_core':
In file included from <module-includes>:1:
gen/third_party/libc++/src/include/__cstddef/byte.h:13:10: fatal error:
'__fwd/byte.h' file not found
13 | #include <__fwd/byte.h>
| ^~~~~~~~~~~~~~
1 error generated.
```
On Thursday, January 15, 2026 at 12:37:21 PM UTC-7 Dustin Breese wrote:
> Hi,
>
> I'm attempting to build V8 14.3.127.17 for Android ARM64. I'm on OSX, but
> using Ubuntu 24.04 docker image to perform the V8 build.
>
> I'm able to successfully install all build deps (install-sysroot.py),
> gclient sync, and even install sysroots
> (build/linux/sysroot_scripts/install-sysroot.py --arch=arm64)
>
> What I am confused about is how to properly configure the build so that
> the android-arm64 build can be loaded and works on Android. Should I be
> using use_custom_libcxx=true or false? Should I be pointing to the NDK
> libc++ libraries instead?
>
> I've spent several days trying different builds and just can't seem to get
> anything working or to understand what the proper approach is. I need to
> embed the v8 engine in my Android app and am currently on a very old V8
> version that DOES BUILD (11.3.42). Any pointers would be appreciated!
>
> I'm a bit confused on what build settings I should use. I was able to
> successfully build the v8 monolith with the following settings, but
> attempting to build and link the lib_monolith.a on Android seems to have a
> libc++ mismatch and fails.
>
> Here's the buildable args.gn:
>
> ```
> target_os="android"
> target_cpu="arm64"
> v8_target_cpu = "arm64"
>
> clang_use_chrome_plugins=false
> dcheck_always_on = false
> icu_use_data_file = false
> is_component_build=false
> is_debug = false
> strip_debug_info=true
> symbol_level=0
> use_libfuzzer=false
> v8_android_log_stdout = true
> v8_enable_handle_zapping=false
> v8_enable_i18n_support=true
> v8_enable_pointer_compression=false
> v8_enable_test_features=false
> v8_enable_webassembly=false
> v8_monolithic=true
> v8_static_library=true
> v8_symbol_level=0
> v8_use_external_startup_data=false
>
> # --- NDK Path Configuration ---
> android_ndk_root = "/v8build/android-ndk-r29"
> android_ndk_version = "r29"
>
> # --- Libc++ Selection ---
> # Disables V8's bundled libc++ so it searches the NDK path instead
> use_custom_libcxx = true
>
> # --- Essential Build Flags ---
> is_clang = true
> ```
>
> Switching to `use_custom_libcxx=false` fails the v8 build in Docker with:
>
> ```
> In file included from <module-includes>:1:
> gen/third_party/libc++/src/include/__cstddef/byte.h:22:1: error: unknown
> type name '_LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD'
> 22 | _LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD
> | ^
> gen/third_party/libc++/src/include/__cstddef/byte.h:57:41: error: no
> template named 'is_integral'; did you mean 'std::is_integral'?
> 57 | template <class _Integer,
> __enable_if_t<is_integral<_Integer>::value, int> = 0>
> | ^
> ...
> ```
>
> Thanks,
> Dustin
>
>
>
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