1 =========================
2 GCC plugin infrastructure
3 =========================
4
5
6 Introduction
7 ============
8
9 GCC plugins are loadable modules that provide extra features to the
10 compiler [1]_. They are useful for runtime instrumentation and static analysis.
11 We can analyse, change and add further code during compilation via
12 callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes [5]_.
13
14 The GCC plugin infrastructure of the kernel supports building out-of-tree
15 modules, cross-compilation and building in a separate directory.
16 Plugin source files have to be compilable by a C++ compiler.
17
18 Currently the GCC plugin infrastructure supports only some architectures.
19 Grep "select HAVE_GCC_PLUGINS" to find out which architectures support
20 GCC plugins.
21
22 This infrastructure was ported from grsecurity [6]_ and PaX [7]_.
23
24 --
25
26 .. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html
27 .. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API
28 .. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html
29 .. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html
30 .. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html
31 .. [6] https://grsecurity.net/
32 .. [7] https://pax.grsecurity.net/
33
34
35 Purpose
36 =======
37
38 GCC plugins are designed to provide a place to experiment with potential
39 compiler features that are neither in GCC nor Clang upstream. Once
40 their utility is proven, the goal is to upstream the feature into GCC
41 (and Clang), and then to finally remove them from the kernel once the
42 feature is available in all supported versions of GCC.
43
44 Specifically, new plugins should implement only features that have no
45 upstream compiler support (in either GCC or Clang).
46
47 When a feature exists in Clang but not GCC, effort should be made to
48 bring the feature to upstream GCC (rather than just as a kernel-specific
49 GCC plugin), so the entire ecosystem can benefit from it.
50
51 Similarly, even if a feature provided by a GCC plugin does *not* exist
52 in Clang, but the feature is proven to be useful, effort should be spent
53 to upstream the feature to GCC (and Clang).
54
55 After a feature is available in upstream GCC, the plugin will be made
56 unbuildable for the corresponding GCC version (and later). Once all
57 kernel-supported versions of GCC provide the feature, the plugin will
58 be removed from the kernel.
59
60
61 Files
62 =====
63
64 **$(src)/scripts/gcc-plugins**
65
66 This is the directory of the GCC plugins.
67
68 **$(src)/scripts/gcc-plugins/gcc-common.h**
69
70 This is a compatibility header for GCC plugins.
71 It should be always included instead of individual gcc headers.
72
73 **$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h,
74 $(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h,
75 $(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h,
76 $(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h**
77
78 These headers automatically generate the registration structures for
79 GIMPLE, SIMPLE_IPA, IPA and RTL passes.
80 They should be preferred to creating the structures by hand.
81
82
83 Usage
84 =====
85
86 You must install the gcc plugin headers for your gcc version,
87 e.g., on Ubuntu for gcc-10::
88
89 apt-get install gcc-10-plugin-dev
90
91 Or on Fedora::
92
93 dnf install gcc-plugin-devel libmpc-devel
94
95 Or on Fedora when using cross-compilers that include plugins::
96
97 dnf install libmpc-devel
98
99 Enable the GCC plugin infrastructure and some plugin(s) you want to use
100 in the kernel config::
101
102 CONFIG_GCC_PLUGINS=y
103 CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
104 ...
105
106 Run gcc (native or cross-compiler) to ensure plugin headers are detected::
107
108 gcc -print-file-name=plugin
109 CROSS_COMPILE=arm-linux-gnu- ${CROSS_COMPILE}gcc -print-file-name=plugin
110
111 The word "plugin" means they are not detected::
112
113 plugin
114
115 A full path means they are detected::
116
117 /usr/lib/gcc/x86_64-redhat-linux/12/plugin
118
119 To compile the minimum tool set including the plugin(s)::
120
121 make scripts
122
123 or just run the kernel make and compile the whole kernel with
124 the cyclomatic complexity GCC plugin.
125
126
127 4. How to add a new GCC plugin
128 ==============================
129
130 The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files
131 right under scripts/gcc-plugins/. Creating subdirectories is not supported.
132 It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins
133 and a relevant Kconfig file.
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