What is a compiler toolchain? - toolchain

Question

From the latest CS:GO update, a valve dev commented this on the reddit post:
We are upgrading the compiler toolchain we use to build CS:GO. This
pre-release branch has CS:GO built with the new toolchain. We are
releasing it as a pre-release branch to allow for testing ahead of it
being used in the next update.
There are no functional changes expected, though the new compiler
toolchain may yield a small performance boost.
Can anyone explain what a compiler toolchain is?

Answer 1

A tool chain is a set of tools (chain of tools) that are used to create a programmed product (runnable/executable program etc.).
Usually toolchains are used in the embedded world for cross-compiling, which means creating a program on a host which will eventually run on a different kind of target - therefore there is a need to create it with a specific compiler, linker, debugger etc.
In order to create from scratch a compiler for the target, you need to cross-compile it with a specific toolchain - that is the compiler toolchain.
So, by using the compiler toolchain you will be able to create a compiler for your target system.

Answer 2

A compiler toolchain is a set of tools, supporting libraries and header files that help build a program from source to an executable that can run on a machine. To see what different tools are invoked during a compilation process pass '-v' flag. e.g., gcc -v hello.c will print the following (Note comments # are mine):
$ /usr/local/Cellar/gcc/11.2.0/bin/gcc-11 -v hello.c
# Configuration options which were used to build gcc itself.
Using built-in specs.
COLLECT_GCC=/usr/local/Cellar/gcc/11.2.0/bin/gcc-11
COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/11.2.0/lto-wrapper
Target: x86_64-apple-darwin20
Configured with: ../configure --prefix=/usr/local/Cellar/gcc/11.2.0 --libdir=/usr/local/Cellar/gcc/11.2.0/lib/gcc/11 --disable-nls --enable-checking=release --enable-languages=c,c++,objc,obj-c++,fortran,d --program-suffix=-11 --with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr --with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl --with-zstd=/usr/local/opt/zstd --with-pkgversion='Homebrew GCC 11.2.0' --with-bugurl=https://github.com/Homebrew/homebrew-core/issues --enable-libphobos --build=x86_64-apple-darwin20 --with-system-zlib --disable-multilib --without-build-config --with-native-system-header-dir=/usr/include --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (Homebrew GCC 11.2.0)
COLLECT_GCC_OPTIONS='-v' '-mmacosx-version-min=11.5.0' '-asm_macosx_version_min=11.5' '-mtune=core2' '-dumpdir' 'a-'
# Compiler invocation of cc1
/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/11.2.0/cc1 -quiet -v -D__DYNAMIC__ hello.c -fPIC -quiet -dumpdir a- -dumpbase hello.c -dumpbase-ext .c -mmacosx-version-min=11.5.0 -mtune=core2 -version -o /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//ccfvEkdl.s
GNU C17 (Homebrew GCC 11.2.0) version 11.2.0 (x86_64-apple-darwin20)
compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include"
ignoring nonexistent directory "/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/../../../../../../x86_64-apple-darwin20/include"
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/include
/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/include-fixed
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks
End of search list.
GNU C17 (Homebrew GCC 11.2.0) version 11.2.0 (x86_64-apple-darwin20)
compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d0f2649375ab2f2193374e77e0a72e7c
COLLECT_GCC_OPTIONS='-v' '-mmacosx-version-min=11.5.0' '-mtune=core2' '-dumpdir' 'a-'
# Assembler invocation
as -arch x86_64 -v -force_cpusubtype_ALL -mmacosx-version-min=11.5 -o /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//cc2nzxXo.o /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//ccfvEkdl.s
Apple clang version 12.0.5 (clang-1205.0.22.9)
Target: x86_64-apple-darwin20.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1as -triple x86_64-apple-macosx11.5.0 -filetype obj -main-file-name ccfvEkdl.s -target-cpu penryn -fdebug-compilation-dir /Users/Coolest -dwarf-debug-producer "Apple clang version 12.0.5 (clang-1205.0.22.9)" -dwarf-version=4 -mrelocation-model pic -mllvm -disable-aligned-alloc-awareness=1 -o /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//cc2nzxXo.o /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//ccfvEkdl.s
COMPILER_PATH=/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/11.2.0/:/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/11.2.0/:/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/:/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/:/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/
LIBRARY_PATH=/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/:/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/../../../
COLLECT_GCC_OPTIONS='-v' '-mmacosx-version-min=11.5.0' '-mtune=core2' '-dumpdir' 'a.'
/usr/local/Cellar/gcc/11.2.0/libexec/gcc/x86_64-apple-darwin20/11.2.0/collect2 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/ -dynamic -arch x86_64 -macosx_version_min 11.5.0 -weak_reference_mismatches non-weak -o a.out -L/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0 -L/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/../../.. /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//cc2nzxXo.o -lSystem -lgcc_ext.10.5 -lgcc -lSystem -no_compact_unwind -v
collect2 version 11.2.0
# linker invocation
/usr/bin/ld -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/ -dynamic -arch x86_64 -macosx_version_min 11.5.0 -weak_reference_mismatches non-weak -o a.out -L/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0 -L/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0/../../.. /var/folders/1n/lll3n8mj6wj975zjw804hg300000gq/T//cc2nzxXo.o -lSystem -lgcc_ext.10.5 -lgcc -lSystem -no_compact_unwind -v
#(#)PROGRAM:ld PROJECT:ld64-650.9
BUILD 00:19:30 Mar 17 2021
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
Library search paths:
/usr/local/Cellar/gcc/11.2.0/lib/gcc/11/gcc/x86_64-apple-darwin20/11.2.0
/usr/local/Cellar/gcc/11.2.0/lib/gcc/11
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib
Framework search paths:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/
Note that a compiler toolchain is necessary to build executables but it is not sufficient. What is missing from the toolchain to have ‘everything’ that is needed to build executable programs is the ‘sysroot’.
Normally when we compile a program for the same machine the compiler uses the standard headers available in ‘/usr/include‘ and libraries from ‘/usr/lib‘. These paths are hardcoded in the compiler itself so we never have to think about it. However, when building a custom compiler or when cross-compiling programs we have to tell the compiler where the sysroot is by passing a flag e.g.
gcc --sysroot="/path/to/arm64/sysroot/usr" hello.c
Most often pre-packaged cross compilers come with a script/binary that has a ‘sysroot’ path embedded into it. e.g., aarch64-linux-gnu-gcc (https://packages.ubuntu.com/xenial/devel/gcc-aarch64-linux-gnu).