编译器

gcc
g++ (GNU, latest version 12 ~ 13)
clang
clang++ (LLVM, latest version 16 ~ 17)

gcc 的优化级别

-O 和 -O1 是等价的。 -O 会对目标文件大小和执行时间进行优化，但不会进行非常耗时的优化，以下是 -O 打开的优化: (其中红色的是 -Og 关闭的)

-fauto-inc-dec
-fbranch-count-reg
-fcombine-stack-adjustments
-fcompare-elim
-fcprop-registers
-fdce
-fdefer-pop
-fdelayed-branch
-fdse
-fforward-propagate
-fguess-branch-probability
-fif-conversion
-fif-conversion2
-finline-functions-called-once
-fipa-modref
-fipa-profile
-fipa-reference
-fipa-reference-addressable
-fmerge-constants
-fmove-loop-invariants
-fmove-loop-stores
-fomit-frame-pointer
-freorder-blocks
-fshrink-wrap
-fshrink-wrap-separate
-fsplit-wide-types
-fssa-backprop
-fssa-phiopt
-ftree-bit-ccp
-ftree-ccp
-ftree-ch
-ftree-coalesce-vars
-ftree-copy-prop
-ftree-dce
-ftree-dominator-opts
-ftree-dse
-ftree-forwprop
-ftree-fre
-ftree-phiprop
-ftree-pta
-ftree-scev-cprop
-ftree-sink
-ftree-slsr
-ftree-sra
-ftree-ter
-funit-at-a-time

链接器

bfd (使用 Binary File Descriptor 库构建的 Linker)
gold (Google linker, faster than bfd, but fewer features)
mold (A modern linker)

动态链接库 (shared library) 无处不在。使用动态链接库基本上是通过链接器 (linker, generally a program suffixing with “ld”)。本文主要回答以下问题:

有哪些链接器?
如何查看一个可执行文件链接哪些动态库?
链接器从哪里找到动态库?

`pkg-config` vs `ldconfig`

pkg-config

dpkg-deb --contents /var/cache/apt/archives/pkg-config_0.29.1-0ubuntu4_amd64.deb

drwxr-xr-x root/root         0 2020-02-07 17:04 ./
drwxr-xr-x root/root         0 2020-02-07 17:04 ./etc/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./etc/dpkg/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./etc/dpkg/dpkg.cfg.d/
-rw-r--r-- root/root       204 2020-02-07 17:04 ./etc/dpkg/dpkg.cfg.d/pkg-config-hook-config
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/bin/
-rwxr-xr-x root/root     55552 2020-02-07 17:04 ./usr/bin/pkg-config
hrwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/bin/x86_64-pc-linux-gnu-pkg-config link to ./usr/bin/pkg-config
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/lib/
-rw-r--r-- root/root        17 2020-02-07 17:04 ./usr/lib/pkg-config.multiarch
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/lib/pkgconfig/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/aclocal/
-rw-r--r-- root/root     10249 2020-02-07 17:04 ./usr/share/aclocal/pkg.m4
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/doc/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/doc/pkg-config/
-rw-r--r-- root/root       359 2014-02-09 01:57 ./usr/share/doc/pkg-config/AUTHORS
-rw-r--r-- root/root      5320 2016-03-02 03:40 ./usr/share/doc/pkg-config/NEWS.gz
-rw-r--r-- root/root      2599 2014-02-09 01:57 ./usr/share/doc/pkg-config/README
-rw-r--r-- root/root      1376 2020-02-07 17:04 ./usr/share/doc/pkg-config/changelog.Debian.gz
-rw-r--r-- root/root       772 2020-02-07 17:04 ./usr/share/doc/pkg-config/copyright
-rw-r--r-- root/root     17832 2020-02-07 17:04 ./usr/share/doc/pkg-config/pkg-config-guide.html
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/man/
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/man/man1/
-rw-r--r-- root/root      7556 2020-02-07 17:04 ./usr/share/man/man1/pkg-config.1.gz
-rwxr-xr-x root/root      2235 2020-02-07 17:04 ./usr/share/pkg-config-crosswrapper
-rwxr-xr-x root/root      1826 2020-02-07 17:04 ./usr/share/pkg-config-dpkghook
drwxr-xr-x root/root         0 2020-02-07 17:04 ./usr/share/pkgconfig/

`lib-dev` 与 `lib` 的区别

$ dpkg -L libxcb1
/.
/usr
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/libxcb.so.1.1.0
/usr/share
/usr/share/doc
/usr/share/doc/libxcb1
/usr/share/doc/libxcb1/changelog.Debian.gz
/usr/share/doc/libxcb1/copyright
/usr/lib/x86_64-linux-gnu/libxcb.so.1

$ dpkg -L libxcb1-dev
/.
/usr
/usr/include
/usr/include/xcb
/usr/include/xcb/bigreq.h
/usr/include/xcb/xc_misc.h
/usr/include/xcb/xcb.h
/usr/include/xcb/xcbext.h
/usr/include/xcb/xproto.h
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/libxcb.a
/usr/lib/x86_64-linux-gnu/pkgconfig
/usr/lib/x86_64-linux-gnu/pkgconfig/xcb.pc
/usr/share
/usr/share/doc
/usr/share/doc/libxcb1-dev
/usr/share/doc/libxcb1-dev/copyright
/usr/lib/x86_64-linux-gnu/libxcb.so
/usr/share/doc/libxcb1-dev/changelog.Debian.gz

`/usr/sbin/ldconfig`

Configure Dynamic Linker Run Time Bindings

#!/bin/sh

if  test $# = 0							\
    && test x"$LDCONFIG_NOTRIGGER" = x				\
 && test x"$DPKG_MAINTSCRIPT_PACKAGE" != x			\
 && dpkg-trigger --check-supported 2>/dev/null
then
	if dpkg-trigger --no-await ldconfig; then
		if test x"$LDCONFIG_TRIGGER_DEBUG" != x; then
			echo "ldconfig: wrapper deferring update (trigger activated)"
		fi
		exit 0
	fi	
fi

exec /sbin/ldconfig.real "$@"

build system

autotools

最近在 Ubuntu 上构建一个软件时遇到以下问题:

1 2	pkg-config --cflags egl # Nothing

打开 pkg-config 的调试模式

pkg-config --cflags egl --debug
  line>prefix=/usr
 Variable declaration, 'prefix' has value '/usr'
  line>libdir=${prefix}/lib/x86_64-linux-gnu
 Variable declaration, 'libdir' has value '/usr/lib/x86_64-linux-gnu'
  line>includedir=${prefix}/include
 Variable declaration, 'includedir' has value '/usr/include'
  line>
  line>Name: EGL
  line>Description: EGL library and headers
  line>Version: 1.5
  line>Libs: -L${libdir} -lEGL
  line>Cflags: -I${includedir}
Path position of 'egl' is 4
Adding 'egl' to list of known packages
Package egl has -I/usr/include in Cflags
Removing -I/usr/include from cflags for egl
Package egl has -L /usr/lib/x86_64-linux-gnu in Libs
Removing -L /usr/lib/x86_64-linux-gnu from libs for egl
  pre-remove: egl
 post-remove: egl
adding CFLAGS_OTHER string ""
  pre-remove: egl
 post-remove: egl
 original: egl
   sorted: egl
adding CFLAGS_I string ""
returning flags string ""

其中的 Package egl has ... 和 Removing ... from cflags for ... 让我十分纳闷。所以想从 pkg-config 的源码一探究竟。当我打开它时，发现它的构建系统还是“古老的” AutoTools.

➜  pg-config git:(master) ✗ ./autogen.sh
+ PROJECT=pkg-config
+ dirname ./autogen.sh
+ srcdir=.
+ test -z .
+ pwd
+ ORIGDIR=/home/luc/gh/pkg-config
+ cd .
+ autoreconf -iv
./autogen.sh: 13: autoreconf: not found
+ exit 127

autotools 包含什么

autoconf
automake
libtool
gettext

meson

-D buildtype

meson 的 buildtype 是用来设定编译优化级别 (optimization levels: -O0, -O1, -O2, -O3, -Os) 和是否有调试信息 (debug: -g)。实际上，meson 提供两个分开的选项分别控制编译优化级别和调试信息

-Doptimization (plain|0|2|3|s, plain 指不设置任何 optimization flags)
-Ddebug (true|false)

use `gold`

1	meson build --prefix=/usr -D{c,cpp}_args=-fuse-ld=gold -Dflavors=x11-gl,x11-glesv2

cmake

use `gold`

1	cmake -B build -DCMAKE_BUILD_TYPE=Debug -DCMAKE_EXPORT_COMPILE_COMMANDS=On -DCMAKE_EXE_LINKER_FLAGS=-fuse-ld=gold

编译 mold

WSL2 Ubuntu 20.04 hosted Windows 11 Dell OptiPlex 3090

$ cmake -B build -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_EXPORT_COMPILE_COMMANDS=On
$ time cmake --build build -j 8
...
[100%] Linking CXX executable mold
[100%] Built target mold
cmake --build build -j 8  844.42s user 94.17s system 674% cpu 2:19.20 total

编译 mesa

➜  forked git:(23.1.3) meson build -Dprefix=/usr/local -Dbuildtype=debug -Dplatforms=x11 -Dvulkan-drivers=swrast -Dgallium-drivers=swrast,radeonsi,panfrost -Dglx=dri -Dllvm=enabled -Dcpp_rtti=false
➜  forked git:(23.1.3) time ninja -C build
ninja: Entering directory `build'
[1559/1559] Generating src/gallium/targets/dri/devenv_panfrost_dri.so with a custom command
ninja -C build  1214.38s user 240.13s system 710% cpu 3:24.62 total

➜  forked git:(23.1.3) ✗ CC=clang CC_LD=mold meson build -Dprefix=/usr/local -Dbuildtype=debug -Dplatforms=x11 -Dvulkan-drivers=swrast -Dgallium-drivers=swrast,radeonsi,panfrost -Dglx=dri -Dllvm=enabled -Dcpp_rtti=false
➜  forked git:(23.1.3) ✗ time ninja -C build
2 warnings generated.
[1559/1559] Generating src/gallium/targets/dri/devenv_mcde_dri.so with a custom command
ninja -C build  12971.24s user 158.32s system 1146% cpu 19:04.81 total

编译 LLVM

主要的配置

cmake -S llvm -B build -G Ninja                                     \
  -DCMAKE_C_COMPILER=gcc-10                                         \
  -DCMAKE_CXX_COMPILER=g++-10                                       \
  -DCMAKE_BUILD_TYPE=Release                                        \
  -DCMAKE_INSTALL_PREFIX="$INSTALL_DIR"                             \
  -DLLVM_LIBDIR_SUFFIX="64"                                         \
  -DLLVM_TARGETS_TO_BUILD="host;AMDGPU"                             \
  -DLLVM_BUILD_LLVM_DYLIB="ON"                                      \
  -DBUILD_SHARED_LIBS="ON"                                          \
  -DLLVM_USE_LINKER="gold"                                          \
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld"              \
  -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"               \
  -DLLVM_PARALLEL_COMPILE_JOBS="1"                                  \
  -DLLVM_PARALLEL_LINK_JOBS="1"

OOM 问题

如果机器内存不够在编译 LLVM 的时候可能会触发 OOM Killer (我在 WSL2 下就100%触发). 可以通过临时添加 swap 分区的方法避免这个问题（Linux Add a Swap File Tutorial）

Build your program

Contents

编译器

gcc 的优化级别

链接器

`pkg-config` vs `ldconfig`

pkg-config

`lib-dev` 与 `lib` 的区别

`/usr/sbin/ldconfig`

build system

autotools

autotools 包含什么

meson

-D buildtype

use `gold`

cmake

use `gold`

编译 mold

编译 mesa

编译 LLVM

主要的配置

OOM 问题

Contents

编译器

gcc 的优化级别

链接器

pkg-config vs ldconfig

pkg-config

lib*-dev 与 lib* 的区别

/usr/sbin/ldconfig

build system

autotools

autotools 包含什么

meson

-D buildtype

use gold

cmake

use gold

编译 mold

编译 mesa

编译 LLVM

主要的配置

OOM 问题

`pkg-config` vs `ldconfig`

`lib-dev` 与 `lib` 的区别

`/usr/sbin/ldconfig`

use `gold`

use `gold`