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docs: Refer to crazylinker as history.

Browse Source 
The crazylinker was removed in crrev.com/1075793, updating the
documentation. It carries some fly-by adjustments in documentation.

Also remove a stale entry from WATCHLISTS.

Bug: 1383210
Change-Id: I529c06e47ebf90ba424860f7005ef9dc3b0ced1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4061632
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Reviewed-by: Eric Foo <efoo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1078026}
This commit is contained in:
Egor Pasko
2022-12-01 14:14:10 +00:00
committed by Chromium LUCI CQ
parent a02a5eaa9f
commit 438cf4e22c
6 changed files with 16 additions and 36 deletions

4
WATCHLISTS

@ -59,9 +59,6 @@
'|components/crash/android/' \
'|components/minidump_uploader/'
},
'android_crazy_linker': {
'filepath': 'third_party/android_crazy_linker/'
},
'android_flags': {
'filepath': 'chrome/android/java/src/org/chromium/chrome/browser/flags/'
},
@ -2257,7 +2254,6 @@
'chikamune+watch@chromium.org'],
'android_crash_reporting': ['asvitkine+watch@chromium.org',
'wnwen+watch@chromium.org'],
'android_crazy_linker': ['johnmaguire+watch@google.com'],
'android_flags': ['hnakashima+watch@chromium.org'],
'android_infobars': ['dfalcantara+watch@chromium.org'],
'android_infra': ['agrieve+watch@chromium.org',

3
base/android/library_loader/README.md

@ -1,8 +1,5 @@
# //base/android/library_loader
Native code is split between this directory and:
* [//third_party/android_crazy_linker](../../../third_party/android_crazy_linker/README.chromium)
Java code lives at:
* [//base/android/java/src/org/chromium/base/library_loader/](../java/src/org/chromium/base/library_loader/)

3
base/android/linker/BUILD.gn

@ -15,9 +15,6 @@ shared_library("chromium_android_linker") {
"linker_minimal_libcxx.cc",
]
# The NDK contains the crazy_linker here:
# '<(android_ndk_root)/crazy_linker.gyp:crazy_linker'
# However, we use our own fork. See bug 384700.
deps = [ "//build:buildflag_header_h" ]
# Export JNI symbols.

7
docs/android_build_instructions.md

@ -184,14 +184,11 @@ depending on the version of Android running on a device. Chrome uses this
feature to package optimized versions for different OS versions.
1. `chrome_modern_public_bundle` (ChromeModernPublic.aab)
* `minSdkVersion=21` (Lollipop).
* Uses [Crazy Linker](https://cs.chromium.org/chromium/src/base/android/linker/BUILD.gn?rcl=6bb29391a86f2be58c626170156cbfaa2cbc5c91&l=9).
* Stores native library with "crazy." prefix to prevent extraction.
* `minSdkVersion=25` (Nougat).
* WebView packaged independently (`system_webview_bundle`).
2. `monochrome_public_bundle` (MonochromePublic.aab)
* `minSdkVersion=24` (Nougat).
* `minSdkVersion=25` (Nougat).
* Contains both Chrome and WebView (to save disk space).
* Does not use Crazy Linker (WebView requires system linker).
3. `trichrome_chrome_bundle` (TrichromeChrome.aab)
* `minSdkVersion=29` (Android 10).
* Native code shared with WebView through a "Static Shared Library APK": `trichrome_library_apk`

33
docs/android_native_libraries.md

@ -5,12 +5,6 @@ Chrome on Android.
[TOC]
## Library Packaging
* Android L & M (ChromeModernPublic.aab):
* `libchrome.so` is stored uncompressed within the apk (with the name
`crazy.libchrome.so` to avoid extraction).
* It is loaded directly from the apk via `libchromium_android_linker.so`.
* Only JNI_OnLoad is exported, since manual JNI registration is required
(see [//base/android/jni_generator/README.md]).
* Android N, O & P (MonochromePublic.aab):
* `libmonochrome.so` is stored uncompressed within the apk (an
AndroidManifest.xml attribute disables extraction).
@ -26,8 +20,6 @@ Chrome on Android.
* It is loaded by `libchromium_android_linker.so` using
`android_dlopen_ext()` to enable RELRO sharing.
[//base/android/jni_generator/README.md]: /base/android/jni_generator/README.md
## Build Variants (eg. monochrome_64_32_apk)
The packaging above extends to cover both 32-bit and 64-bit device
configurations.
@ -147,7 +139,6 @@ Builds on | Variant | Chrome | Library | Webview
* For ChromePublic.apk:
* `JNI_OnLoad()` is the only exported symbol (enforced by a linker script).
* Native methods registered explicitly during start-up by generated code.
* Explicit generation is required because the Android runtime uses the system's `dlsym()`, which doesn't know about Crazy-Linker-opened libraries.
* For MonochromePublic.apk and TrichromeChrome.aab:
* `JNI_OnLoad()` and `Java_*` symbols are exported by linker script.
* No manual JNI registration is done. Symbols are resolved lazily by the runtime.
@ -172,16 +163,6 @@ Builds on | Variant | Chrome | Library | Webview
* Processes `fork()`ed from the app zygote (where the library is loaded) share RELRO (via `fork()`'s copy-on-write semantics), but this region is not shared with other process types (privileged, utility, GPU)
**How does it work?**
* For Android < N (crazy linker):
1. Browser Process: `libchrome.so` loaded normally.
2. Browser Process: `GNU_RELRO` segment copied into `ashmem` (shared memory).
3. Browser Process (low-end only): RELRO private memory pages swapped out for ashmem ones (using `munmap()` & `mmap()`).
4. Browser Process: Load address and shared memory fd passed to renderers / gpu process.
5. Renderer Process: Crazy linker tries to load to the given load address.
* Loading can fail due to address space randomization causing something else to already by loaded at the address.
6. Renderer Process: If loading to the desired address succeeds:
* Linker puts `GNU_RELRO` into private memory and applies relocations as per normal.
* Afterwards, memory pages are compared against the shared memory and all identical pages are swapped out for ashmem ones (using `munmap()` & `mmap()`).
* For a more detailed description, refer to comments in [Linker.java](https://cs.chromium.org/chromium/src/base/android/java/src/org/chromium/base/library_loader/Linker.java).
* For Android N-P:
* The OS maintains a RELRO file on disk with the contents of the GNU_RELRO segment.
@ -204,6 +185,13 @@ Builds on | Variant | Chrome | Library | Webview
app zygote. `libmonochrome.so` is loaded in the zygote before `fork()`.
* Similar to O-P, app zygote provides copy-on-write memory semantics so
RELRO sharing is redundant.
* For Android R+ (still Trichrome)
* The RELRO region is created in the App Zygote, picked up by the Browser
process, which then redistributes the region to all other processes. The
receiving of the region and remapping it on top of the non-shared RELRO
happens asynchronously after the library has been loaded. Native code is
generally already running at this point. Hence the replacement must be
atomic.
## Partitioned libraries
Some Chrome code is placed in feature-specific libraries and delivered via
@ -267,6 +255,13 @@ Partitioned libraries are usable when all of the following are true:
* This was removed due to [poor performance](https://bugs.chromium.org/p/chromium/issues/detail?id=719977).
* We used to use `relocation_packer` to pack relocations after linking, which complicated our build system and caused many problems for our tools because it caused logical addresses to differ from physical addresses.
* We now link with `lld`, which supports packed relocations natively and doesn't have these problems.
* We used to use the Crazy Linker until Android M was deprecated
* It allowed storing `libchrome.so` uncompressed within the apk before the
system linker allowed it (with the name `crazy.libchrome.so` to avoid extraction).
* It was loaded directly from the apk via `libchromium_android_linker.so`.
* Only JNI_OnLoad was exported. Explicit JNI registration was required
because the Android runtime uses the system's `dlsym()`, which doesn't know
about Crazy-Linker-opened libraries. (see [//base/android/jni_generator/README.md]).
## See Also
* [//docs/android_build_instructions.md#Multiple-Chrome-APK-Targets](android_build_instructions.md#Multiple-Chrome-APK-Targets)

2
infra/inclusive_language_presubmit_exempt_dirs.txt

@ -261,8 +261,6 @@ third_party/afl/src 3 1
third_party/afl/src/docs 11 2
third_party/afl/src/llvm_mode 1 1
third_party/afl/src/qemu_mode 1 1
third_party/android_crazy_linker 1 1
third_party/android_crazy_linker/src/src 1 1
third_party/android_deps 1 1
third_party/android_deps_autorolled 1 1
third_party/android_deps/buildSrc/src/main/groovy 25 2