How to use randen_engine under src\third_party\blink\renderer\core

[FlyingEagle]

Hi,

I have not found real example in Chromium 

what I am trying to use is:

typedef absl::randen_engine<uint64_t> FarblingPRNG;

int BraveSessionCache::FarbledInteger(FarbleKey key,

                                      int spoof_value,

                                      int min_random_offset,

                                      int max_random_offset) {

  if (farbled_integers_.count(key) == 0) {

    FarblingPRNG prng = MakePseudoRandomGenerator(key);

    farbled_integers_[key] =

        prng() % (1 + max_random_offset - min_random_offset) +

        min_random_offset;

  }

  return farbled_integers_[key] + spoof_value;

}

file structure is as below:

but failed

c:\code\chromium_git\chromium\src>ninja -C out\Release_GN_x86 cef

ninja: Entering directory `out\Release_GN_x86'

[0/1] Regenerating ninja files

[1/335] LINK v8_context_snapshot_generator.exe v8_context_snapshot_generator.exe.pdb

FAILED: v8_context_snapshot_generator.exe v8_context_snapshot_generator.exe.pdb

ninja -t msvc -e environment.x86 -- ..\..\third_party\llvm-build\Release+Asserts\bin\lld-link.exe /nologo -libpath:..\..\third_party\llvm-build\Release+Asserts\lib\clang\12.0.0\lib\windows "-libpath:..\..\..\..\..\..\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\ATLMFC\lib\x86" "-libpath:..\..\..\..\..\..\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\lib\x86" "-libpath:..\..\..\..\..\..\Program Files (x86)\Windows Kits\10\lib\10.0.19041.0\ucrt\x86" "-libpath:..\..\..\..\..\..\Program Files (x86)\Windows Kits\10\lib\10.0.19041.0\um\x86" /OUT:./v8_context_snapshot_generator.exe /PDB:./v8_context_snapshot_generator.exe.pdb @./v8_context_snapshot_generator.exe.rsp

lld-link: error: undefined symbol: public: __thiscall absl::random_internal::Randen::Randen(void)

>>> referenced by .\..\..\third_party\blink\renderer\core\farbling\brave_session_cache.cc:357

>>>               blink_core.lib(brave_session_cache.obj):(public: bool __thiscall brave::BraveSessionCache::AllowFontFamily(class blink::WebContentSettingsClient *, class WTF::AtomicString const &))

>>> referenced by .\..\..\third_party\blink\renderer\core\farbling\brave_session_cache.cc:343

>>>               blink_core.lib(brave_session_cache.obj):(public: int __thiscall brave::BraveSessionCache::FarbledInteger(enum brave::FarbleKey, int, int, int))

>>> referenced by .\..\..\third_party\blink\renderer\core\farbling\brave_session_cache.cc:329

>>>               blink_core.lib(brave_session_cache.obj):(public: class WTF::String __thiscall brave::BraveSessionCache::FarbledUserAgent(class WTF::String))

>>> referenced 1 more times

lld-link: error: undefined symbol: public: static void __cdecl absl::random_internal::RandenSlow::Generate(void const *, void *)

seems that abseil-cpp obj files are not generated in out folder.

then I add deps as

but failed as below

c:\code\chromium_git\chromium\src>ninja -C out\Release_GN_x86 cef

ninja: Entering directory `out\Release_GN_x86'

[0/1] Regenerating ninja files

ERROR Unresolved dependencies.

//third_party/blink/renderer/core:core(//build/toolchain/win:win_clang_x86)

  needs //third_party/abseil-cpp:abseil-cpp(//build/toolchain/win:win_clang_x86)

how to use abseil-cpp in a correct way? under src\third_party\blink\renderer\core

thx

[Derek Mauro]

For Chromium, I think the correct answer is don't use Abseil's Random library at all. Please see https://chromium.googlesource.com/chromium/src/+/HEAD/styleguide/c++/c++-features.md#Random-banned.

Hypothetically, if this were not Chromium, randen_engine is defined in absl/random/internal/randen_engine.h. The "internal" in the path means that it should not be used directly at all. Instead, use absl::BitGen. absl::BitGen makes no claims about the underlying engine, and we may delete or replace randen_engine at any time. See https://abseil.io/docs/cpp/guides/random for more information about supported use.

The error you are seeing looks like a linker error, which generally means a dependency is missing somewhere. I don't know anything about Chromium's build system, so you really need to do this, you will have to get help from Chromium.

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[wei cheng]

very kind and detailed replay, thanks, I'll try to turn to chromium groups or check if there are some other solution.