Android 16 KB page sizes

[Mati Cohen]

Hi,

My app is using v8 to run a JS environment. Last time I built v8 was about 3 years ago by pointing to 10.4.132.

As per Google policy, my app needs to support 16 KB page size and I've been checking all my dependencies to meet that criteria.

Apparently, based on my checks, my v8 build does support it and I managed to run the app on my device.

However, v8 is crashing as soon as I call V8::Initialize(); with the following stack trace:

/base.apk!liben8.so (offset 0x8ad8000) (v8::base::OS::Abort()+28)

/base.apk!liben8.so (offset 0x8ad8000) (V8_Fatal(char const*, ...)+376)
/base.apk!liben8.so (offset 0x8ad8000) (v8::base::OS::SetDataReadOnly(void*, unsigned long)+52)
/base.apk!liben8.so (offset 0x8ad8000) (v8::internal::V8::Initialize()+1552)

/base.apk!liben8.so (offset 0x8ad8000) (v8::V8::Initialize(int)+28)

/base.apk!liben8.so (offset 0x8ad8000) (Runtime::Runtime(_JNIEnv*)+172)

As explained at https://developer.android.com/guide/practices/page-sizes#check-code, I was trying to look for references to PAGE_SIZE and 4096 to see if I was setting up something wrong, but I didn't find anything.

Does anyone have any knowledge about this?

Thanks a lot,

Mati

[Ben Noordhuis]

V8 doesn't use PAGE_SIZE, it uses sysconf(_SC_PAGESIZE).

You mention 10.4.132 but that stack trace is from a different version,
isn't it? Because SetDataReadOnly didn't exist back then.

It crashes when trying to mprotect(PROT_READ) the command line flags,
v8_flags. v8_flags is aligned to kMinimumOSPageSize and that _should_
be 16k on Android but you'll want to double-check that. It's defined
in src/base/build_config.h.

What error message did V8 print?

[Matias Cohen]

Thanks Ben.

Yeah, that’s strange. I also noticed that SetDataReadOnly didn’t exist in 10.4.132. Moreover, the V8_FATAL exception that is raised was added even later. Maybe my records about 10.4.132 are wrong, but I am sure that we built v8 last time in August 2022, so I can’t explain it.

Android Studio don’t show any error message more than the stacktrace I already shared.

My guess is that kMinimumOSPageSize was still 4KB for Android back then when I built v8 (yet I can’t explain why SetDataReadOnly is part of the stacktrace).

Is there any way for me to overwrite kMinimumOSPageSize from “outside” v8, just to test if that makes a difference?

Thanks!

> On Sep 12, 2025, at 5:20 AM, Ben Noordhuis <in...@bnoordhuis.nl> wrote:
>
> On Fri, Sep 12, 2025 at 8:26 AM 'Mati Cohen' via v8-users
> <v8-u...@googlegroups.com> wrote:
>>
>> Hi,
>>
>> My app is using v8 to run a JS environment. Last time I built v8 was about 3 years ago by pointing to 10.4.132.
>>
>> As per Google policy, my app needs to support 16 KB page size and I've been checking all my dependencies to meet that criteria.
>>
>> Apparently, based on my checks, my v8 build does support it and I managed to run the app on my device.
>> However, v8 is crashing as soon as I call V8::Initialize(); with the following stack trace:
>>
>> /base.apk!liben8.so (offset 0x8ad8000) (v8::base::OS::Abort()+28)
>> /base.apk!liben8.so (offset 0x8ad8000) (V8_Fatal(char const*, ...)+376)
>> /base.apk!liben8.so (offset 0x8ad8000) (v8::base::OS::SetDataReadOnly(void*, unsigned long)+52)
>> /base.apk!liben8.so (offset 0x8ad8000) (v8::internal::V8::Initialize()+1552)
>> /base.apk!liben8.so (offset 0x8ad8000) (v8::V8::Initialize(int)+28)
>> /base.apk!liben8.so (offset 0x8ad8000) (Runtime::Runtime(_JNIEnv*)+172)
>>

>> As explained at https://www.google.com/url?q=https://developer.android.com/guide/practices/page-sizes%23check-code&source=gmail-imap&ust=1758273654000000&usg=AOvVaw2eBFhXRa0E0P-iWsikoJCW, I was trying to look for references to PAGE_SIZE and 4096 to see if I was setting up something wrong, but I didn't find anything.

>>
>> Does anyone have any knowledge about this?
>> Thanks a lot,
>> Mati
>
> V8 doesn't use PAGE_SIZE, it uses sysconf(_SC_PAGESIZE).
>
> You mention 10.4.132 but that stack trace is from a different version,
> isn't it? Because SetDataReadOnly didn't exist back then.
>
> It crashes when trying to mprotect(PROT_READ) the command line flags,
> v8_flags. v8_flags is aligned to kMinimumOSPageSize and that _should_
> be 16k on Android but you'll want to double-check that. It's defined
> in src/base/build_config.h.
>
> What error message did V8 print?
>

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[Ben Noordhuis]

Assuming recompiling is not a problem for you: just edit
build_config.h and change it to 16k.

IIRC, stdout and stderr are not normally hooked up to anything on
Android but it should be possible to freopen them to a log file.

On Fri, Sep 12, 2025 at 4:15 PM 'Matias Cohen' via v8-users

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[Mati Cohen]

I'm willing to recompile the latest stable version. I am looking at build_config.h and for it's using the following implementation:

#if (defined(V8_OS_MACOS) && defined(V8_HOST_ARCH_ARM64)) || \

(defined(V8_OS_ANDROID) && \

(defined(V8_HOST_ARCH_ARM64) || defined(V8_HOST_ARCH_X64))) || \

defined(V8_HOST_ARCH_LOONG64) || defined(V8_HOST_ARCH_MIPS64) || \

defined(V8_OS_IOS)

// Android 64 bit has experimental support for 16kB pages.

// MacOS & iOS on arm64 uses 16kB pages.

// LOONG64 and MIPS64 also use 16kB pages.

constexpr int kMinimumOSPageSize = 16 * 1024;

#elif defined(V8_OS_LINUX) && !defined(V8_OS_ANDROID) && \

(defined(V8_HOST_ARCH_ARM64) || defined(V8_HOST_ARCH_PPC64))

// Linux on arm64 (excluding android) and PPC64 can be configured for up to 64kB

// pages.

constexpr int kMinimumOSPageSize = 64 * 1024;

#else

// Everything else uses 4kB pages.

constexpr int kMinimumOSPageSize = 4 * 1024;

#endif

Sorry for my ignorance, but does it mean that all Android devices with arm64-v8a and x86_64 architectures will use a size of 16KB. Is this correct? I am trying to understand if there are devices with arm64-v8a and x86_64 architectures which still use 4KB for page sizes.

Thanks,

Matias.

[Mati Cohen]

Sorry, in addition to my above question:

I've started to set up my environment to build v8 (14.0.263.4).

When I run the following command:

local arch=$1

local output_dir=$2

local config=()

# building for Android on a specific arch

config+=('target_os="android"')

config+=("target_cpu=\"$arch\"")

config+=("v8_target_cpu=\"$arch\"")

# release configuration

config+=('is_debug=false')

config+=('symbol_level=0')

config+=('android_unstripped_runtime_outputs=false')

# static library

config+=('is_component_build=false')

config+=('v8_static_library=true')

config+=('v8_monolithic=true')

# use builtin snapshotting

config+=('v8_use_external_startup_data=false')

# disable i18n to reduce size

config+=('v8_enable_i18n_support=false')

# log everything to stdout on Android

config+=('v8_android_log_stdout=true')

# starting from v8 9.9 custom libc compiler causes overlaping issues with libstdc++.

# we should explicitly disable it

config+=('use_custom_libcxx=false')

tools/dev/v8gen.py -vv -b android.arm.release "$output_dir" -- "${config[@]}"

It fails with the following message:

  /mnt/upstream/v8/buildtools/linux64/gn gen out.gn/arm64-v8a --check
    -> returned 1
  ERROR at //gni/snapshot_toolchain.gni:115:1: Assertion failed.
  assert(v8_snapshot_toolchain != "",
  ^-----
  Do not know how to build a snapshot for //build/toolchain/android:android_clang_arm on linux arm64
  See //BUILD.gn:17:1: whence it was imported.
  import("gni/snapshot_toolchain.gni")
  ^----------------------------------
  GN gen failed: 1

And I also get this (before):

  Writing """\
  android_unstripped_runtime_outputs = false
  dcheck_always_on = false
  default_min_sdk_version = 21
  is_debug = false
  target_cpu = "arm"
  target_os = "android"
  v8_android_log_stdout = true
  """ to /mnt/upstream/v8/out.gn/arm64-v8a/args.gn.

It looks like my arguments are being ignored. However, if I go to v8/infra/mb/mb_config.pyl and I hardcode my flags in the android mixin it works properly.

Is there a bug or am I running something wrong?

Thanks,

Mati.

[Mati Cohen]

Sorry, I already fixed my problem. It was related to my Apple Silicon chip and docker.

If anyone face this issue, I solved it by running docker like this:

FROM --platform=linux/amd64 ubuntu:latest

Thanks,
Matias

[Ben Noordhuis]

Yes, 16k on x64 and arm64 android.

On Tue, Sep 16, 2025 at 6:53 PM 'Mati Cohen' via v8-users

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