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a8d39b88406e2047746366355666b5f603105a2e doc: explain why passing -mlinker-version is required (fanquake) Pull request description: I have been down a 🐇 hole. Closes #19359. When Clang is compiled, [a check is run](https://github.com/llvm/llvm-project/blob/release/8.x/clang/CMakeLists.txt#L353) to define `HOST_LINK_VERSION` as the output of `$CMAKE_LINKER -v`. Note the this is the version of the linker being used to compile Clang itself.. and this check is only run when compiling Clang for macOS. In the Clang driver, if `HOST_LINK_VERSION` has been defined, there is some additional runtime functionality. An `-mlinker-version` argument, with the value of `HOST_LINK_VERSION` [will be added to the linker arguments](89de0d8dfb/clang/lib/Driver/Driver.cpp (L382)), if `-mlinker-version` has not been passed in by the user. This is a bit weird, as by default, you are setting `-mlinker-version` to the version of the linker that was used to build the Clang binary, not the linker which will be used when compiling. The commit which introduced the functionality,628fcf4e3b, described it as a "hack", that should be replaced. However, that was 10 years ago, and the behaviour is still here. In the Darwin driver, [a check is done](89de0d8dfb/clang/lib/Driver/ToolChains/Darwin.cpp (L208)) for the `-mlinker-version` argument. If there is no argument, the version will default to `0`. Given the above, this should never happen when using Clang for macOS. A series of comparisons are then performed, to check whether the linker version is modern enough to enable certain features, like [`-demangle`](89de0d8dfb/clang/lib/Driver/ToolChains/Darwin.cpp (L215)). ### What this means #### macOS A Clang compiled for macOS, i.e `clang+llvm-8.0.0-x86_64-apple-darwin`, will have `HOST_LINKER_VERSION` set to the version of the linker used to compile Clang itself. At runtime, `-mlinker-version=HOST_LINKER_VERSION` will be added to the linker args, if `-mlinker-version` wasn't passed in. In the Darwin driver, additional arguments, like `-demangle`, will be added to the linker arguments, because `HOST_LINKER_VERSION` was likely some very modern version of `lld` or `ld64`. #### Linux (cross compilation in depends) A Clang compiled for Linux, i.e `clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-14.04`, which we now use for macOS builds in depends, will behave differently. As it's built for Linux, `HOST_LINKER_VERSION` was not defined at compile time, and there will be no default behaviour of appending `-mlinker-version=HOST_LINKER_VERSION` to the linker args. Thus, unless you pass in `-mlinker-version` yourself, when the version checks are done in the Darwin driver, no modern linker features will be enabled, as the version will have defaulted to `0`. Therefore, it's important that we continue to pass `-mlinker-version="our LD64 version"` as part of our compilation flags, if we want to have "modern" linker features enabled for our macOS builds. #### Summary [Clang 8](https://releases.llvm.org/download.html#8.0.0). Building a macOS binary. Link line with path arguments trimmed. | | default behaviour | `-mlinker-version=100` (`-demangle threshold`) | `-mlinker-version=530` | | - | --------------- | --------------------- | ---------------------- | | macOS Clang | `-demangle -lto_library ../libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.15.0 -o a.out ../test-b8b9b3.o -lc++ -lSystem ../libclang_rt.osx.a` | `-demangle -dynamic -arch x86_64 -macosx_version_min 10.15.0 -o a.out ../test-a66966.o -lc++ -lSystem ../libclang_rt.osx.a` | same as default | | Linux Clang | `-dynamic -arch x86_64 -macosx_version_min 10.12.0 -o a.out ../test-bfce57.o -lc++ -lSystem` | `-demangle -dynamic -arch x86_64 -macosx_version_min 10.12.0 -o a.out ../test-a846a3.o -lc++ -lSystem` | `-demangle -lto_library ../libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.12.0 -o a.out ../test-de0280.o -lc++ -lSystem` | Note: Most links here are pointing to the 8.x branch of LLVM/Clang, as we are using that version in depends. Note: To add a little more confusion, you wont see `-mlinker-version X` in your compile flags, you'll see [`-target-linker-version X`](431daedee4/clang/lib/Driver/ToolChains/Clang.cpp (L4777)). ACKs for top commit: laanwj: ACK a8d39b88406e2047746366355666b5f603105a2e Tree-SHA512: 92f93079a5e59a0d561e74336b5cb03e3bf5a34437f5850283b9128c7624494b8285ec16290b1fa8103fe87f8789a53ce44b17902b8c1db5fde24d74b76fb168
Usage
To build dependencies for the current arch+OS:
make
To build for another arch/OS:
make HOST=host-platform-triplet
For example:
make HOST=x86_64-w64-mingw32 -j4
Bitcoin Core's configure script by default will ignore the depends output. In
order for it to pick up libraries, tools, and settings from the depends build,
you must point it at the appropriate --prefix directory generated by the
build. In the above example, a prefix dir named x86_64-w64-mingw32 will be
created. To use it for Bitcoin:
./configure --prefix=$PWD/depends/x86_64-w64-mingw32
Common host-platform-triplets for cross compilation are:
i686-pc-linux-gnufor Linux 32 bitx86_64-pc-linux-gnufor x86 Linuxx86_64-w64-mingw32for Win64x86_64-apple-darwin16for macOSarm-linux-gnueabihffor Linux ARM 32 bitaarch64-linux-gnufor Linux ARM 64 bitpowerpc64-linux-gnufor Linux POWER 64-bit (big endian)powerpc64le-linux-gnufor Linux POWER 64-bit (little endian)riscv32-linux-gnufor Linux RISC-V 32 bitriscv64-linux-gnufor Linux RISC-V 64 bits390x-linux-gnufor Linux S390Xarmv7a-linux-androidfor Android ARM 32 bitaarch64-linux-androidfor Android ARM 64 biti686-linux-androidfor Android x86 32 bitx86_64-linux-androidfor Android x86 64 bit
The paths are automatically configured and no other options are needed unless targeting Android.
Install the required dependencies: Ubuntu & Debian
For macOS cross compilation
sudo apt-get install curl librsvg2-bin libtiff-tools bsdmainutils cmake imagemagick libcap-dev libz-dev libbz2-dev python3-setuptools
For Win64 cross compilation
- see build-windows.md
For linux (including i386, ARM) cross compilation
Common linux dependencies:
sudo apt-get install make automake cmake curl g++-multilib libtool binutils-gold bsdmainutils pkg-config python3 patch
For linux ARM cross compilation:
sudo apt-get install g++-arm-linux-gnueabihf binutils-arm-linux-gnueabihf
For linux AARCH64 cross compilation:
sudo apt-get install g++-aarch64-linux-gnu binutils-aarch64-linux-gnu
For linux POWER 64-bit cross compilation (there are no packages for 32-bit):
sudo apt-get install g++-powerpc64-linux-gnu binutils-powerpc64-linux-gnu g++-powerpc64le-linux-gnu binutils-powerpc64le-linux-gnu
For linux RISC-V 64-bit cross compilation (there are no packages for 32-bit):
sudo apt-get install g++-riscv64-linux-gnu binutils-riscv64-linux-gnu
RISC-V known issue: gcc-7.3.0 and gcc-7.3.1 result in a broken test_bitcoin executable (see https://github.com/bitcoin/bitcoin/pull/13543),
this is apparently fixed in gcc-8.1.0.
For linux S390X cross compilation:
sudo apt-get install g++-s390x-linux-gnu binutils-s390x-linux-gnu
Dependency Options
The following can be set when running make: make FOO=bar
SOURCES_PATH: downloaded sources will be placed here
BASE_CACHE: built packages will be placed here
SDK_PATH: Path where sdk's can be found (used by macOS)
FALLBACK_DOWNLOAD_PATH: If a source file can't be fetched, try here before giving up
NO_QT: Don't download/build/cache qt and its dependencies
NO_QR: Don't download/build/cache packages needed for enabling qrencode
NO_ZMQ: Don't download/build/cache packages needed for enabling zeromq
NO_WALLET: Don't download/build/cache libs needed to enable the wallet
NO_UPNP: Don't download/build/cache packages needed for enabling upnp
MULTIPROCESS: build libmultiprocess (experimental, requires cmake)
DEBUG: disable some optimizations and enable more runtime checking
HOST_ID_SALT: Optional salt to use when generating host package ids
BUILD_ID_SALT: Optional salt to use when generating build package ids
If some packages are not built, for example make NO_WALLET=1, the appropriate
options will be passed to bitcoin's configure. In this case, --disable-wallet.
Additional targets
download: run 'make download' to fetch all sources without building them
download-osx: run 'make download-osx' to fetch all sources needed for macOS builds
download-win: run 'make download-win' to fetch all sources needed for win builds
download-linux: run 'make download-linux' to fetch all sources needed for linux builds
Android
Before proceeding with an Android build one needs to get the Android SDK and use the "SDK Manager" tool to download the NDK and one or more "Platform packages" (these are Android versions and have a corresponding API level).
In order to build ANDROID_API_LEVEL (API level corresponding to the Android version targeted, e.g. Android 9.0 Pie is 28 and its "Platform package" needs to be available) and ANDROID_TOOLCHAIN_BIN (path to toolchain binaries depending on the platform the build is being performed on) need to be set.
API levels from 24 to 29 have been tested to work.
If the build includes Qt, environment variables ANDROID_SDK and ANDROID_NDK need to be set as well but can otherwise be omitted.
This is an example command for a default build with no disabled dependencies:
ANDROID_SDK=/home/user/Android/Sdk ANDROID_NDK=/home/user/Android/Sdk/ndk-bundle make HOST=aarch64-linux-android ANDROID_API_LEVEL=28 ANDROID_TOOLCHAIN_BIN=/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin
Other documentation
- description.md: General description of the depends system
- packages.md: Steps for adding packages