From 8bd51a2ba3c3bb81a693fff17e983d02d914c14c Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 20 Oct 2021 10:35:53 -0700 Subject: gcc-plugins: Explicitly document purpose and deprecation schedule GCC plugins should only exist when some compiler feature needs to be proven but does not exist in either GCC nor Clang. For example, if a desired feature is already in Clang, it should be added to GCC upstream. Document this explicitly. Additionally, mark the plugins with matching upstream GCC features as removable past their respective GCC versions. Cc: Masahiro Yamada Cc: Michal Marek Cc: Nick Desaulniers Cc: Jonathan Corbet Cc: James Morris Cc: "Serge E. Hallyn" Cc: Nathan Chancellor Cc: linux-hardening@vger.kernel.org Cc: linux-kbuild@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-security-module@vger.kernel.org Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook Reviewed-by: Nathan Chancellor Reviewed-by: Miguel Ojeda Acked-by: Nick Desaulniers Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20211020173554.38122-2-keescook@chromium.org --- Documentation/kbuild/gcc-plugins.rst | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'Documentation') diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst index 3349966f213d..4b28c7a4032f 100644 --- a/Documentation/kbuild/gcc-plugins.rst +++ b/Documentation/kbuild/gcc-plugins.rst @@ -32,6 +32,32 @@ This infrastructure was ported from grsecurity [6]_ and PaX [7]_. .. [7] https://pax.grsecurity.net/ +Purpose +======= + +GCC plugins are designed to provide a place to experiment with potential +compiler features that are neither in GCC nor Clang upstream. Once +their utility is proven, the goal is to upstream the feature into GCC +(and Clang), and then to finally remove them from the kernel once the +feature is available in all supported versions of GCC. + +Specifically, new plugins should implement only features that have no +upstream compiler support (in either GCC or Clang). + +When a feature exists in Clang but not GCC, effort should be made to +bring the feature to upstream GCC (rather than just as a kernel-specific +GCC plugin), so the entire ecosystem can benefit from it. + +Similarly, even if a feature provided by a GCC plugin does *not* exist +in Clang, but the feature is proven to be useful, effort should be spent +to upstream the feature to GCC (and Clang). + +After a feature is available in upstream GCC, the plugin will be made +unbuildable for the corresponding GCC version (and later). Once all +kernel-supported versions of GCC provide the feature, the plugin will +be removed from the kernel. + + Files ===== -- cgit v1.2.3 From b4d89579ccb1ad5ffcdb3430933ce1e31a009ec7 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 20 Oct 2021 10:35:54 -0700 Subject: gcc-plugins: Remove cyc_complexity This plugin has no impact on the resulting binary, is disabled under COMPILE_TEST, and is not enabled on any builds I'm aware of. Additionally, given the clarified purpose of GCC plugins in the kernel, remove cyc_complexity. Cc: Masahiro Yamada Cc: Michal Marek Cc: Nick Desaulniers Cc: Jonathan Corbet Cc: linux-hardening@vger.kernel.org Cc: linux-kbuild@vger.kernel.org Cc: linux-doc@vger.kernel.org Signed-off-by: Kees Cook Reviewed-by: Miguel Ojeda Reviewed-by: Nathan Chancellor Acked-by: Nick Desaulniers Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20211020173554.38122-3-keescook@chromium.org --- Documentation/kbuild/gcc-plugins.rst | 2 - scripts/Makefile.gcc-plugins | 2 - scripts/gcc-plugins/Kconfig | 16 ------- scripts/gcc-plugins/cyc_complexity_plugin.c | 69 ----------------------------- 4 files changed, 89 deletions(-) delete mode 100644 scripts/gcc-plugins/cyc_complexity_plugin.c (limited to 'Documentation') diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst index 4b28c7a4032f..0ba76719f1b9 100644 --- a/Documentation/kbuild/gcc-plugins.rst +++ b/Documentation/kbuild/gcc-plugins.rst @@ -96,7 +96,6 @@ Enable the GCC plugin infrastructure and some plugin(s) you want to use in the kernel config:: CONFIG_GCC_PLUGINS=y - CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=y CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y ... @@ -115,4 +114,3 @@ The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files right under scripts/gcc-plugins/. Creating subdirectories is not supported. It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins and a relevant Kconfig file. -See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin. diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins index 952e46876329..6583ecf2e674 100644 --- a/scripts/Makefile.gcc-plugins +++ b/scripts/Makefile.gcc-plugins @@ -1,7 +1,5 @@ # SPDX-License-Identifier: GPL-2.0 -gcc-plugin-$(CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) += cyc_complexity_plugin.so - gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY) += latent_entropy_plugin.so gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY) \ += -DLATENT_ENTROPY_PLUGIN diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig index 7c7ba3b0d3cd..51d81c3f03d6 100644 --- a/scripts/gcc-plugins/Kconfig +++ b/scripts/gcc-plugins/Kconfig @@ -19,22 +19,6 @@ menuconfig GCC_PLUGINS if GCC_PLUGINS -config GCC_PLUGIN_CYC_COMPLEXITY - bool "Compute the cyclomatic complexity of a function" if EXPERT - depends on !COMPILE_TEST # too noisy - help - The complexity M of a function's control flow graph is defined as: - M = E - N + 2P - where - - E = the number of edges - N = the number of nodes - P = the number of connected components (exit nodes). - - Enabling this plugin reports the complexity to stderr during the - build. It mainly serves as a simple example of how to create a - gcc plugin for the kernel. - config GCC_PLUGIN_SANCOV bool # Plugin can be removed once the kernel only supports GCC 6+ diff --git a/scripts/gcc-plugins/cyc_complexity_plugin.c b/scripts/gcc-plugins/cyc_complexity_plugin.c deleted file mode 100644 index 73124c2b3edd..000000000000 --- a/scripts/gcc-plugins/cyc_complexity_plugin.c +++ /dev/null @@ -1,69 +0,0 @@ -/* - * Copyright 2011-2016 by Emese Revfy - * Licensed under the GPL v2, or (at your option) v3 - * - * Homepage: - * https://github.com/ephox-gcc-plugins/cyclomatic_complexity - * - * https://en.wikipedia.org/wiki/Cyclomatic_complexity - * The complexity M is then defined as: - * M = E - N + 2P - * where - * - * E = the number of edges of the graph - * N = the number of nodes of the graph - * P = the number of connected components (exit nodes). - * - * Usage (4.5 - 5): - * $ make clean; make run - */ - -#include "gcc-common.h" - -__visible int plugin_is_GPL_compatible; - -static struct plugin_info cyc_complexity_plugin_info = { - .version = "20160225", - .help = "Cyclomatic Complexity\n", -}; - -static unsigned int cyc_complexity_execute(void) -{ - int complexity; - expanded_location xloc; - - /* M = E - N + 2P */ - complexity = n_edges_for_fn(cfun) - n_basic_blocks_for_fn(cfun) + 2; - - xloc = expand_location(DECL_SOURCE_LOCATION(current_function_decl)); - fprintf(stderr, "Cyclomatic Complexity %d %s:%s\n", complexity, - xloc.file, DECL_NAME_POINTER(current_function_decl)); - - return 0; -} - -#define PASS_NAME cyc_complexity - -#define NO_GATE -#define TODO_FLAGS_FINISH TODO_dump_func - -#include "gcc-generate-gimple-pass.h" - -__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) -{ - const char * const plugin_name = plugin_info->base_name; - - PASS_INFO(cyc_complexity, "ssa", 1, PASS_POS_INSERT_AFTER); - - if (!plugin_default_version_check(version, &gcc_version)) { - error(G_("incompatible gcc/plugin versions")); - return 1; - } - - register_callback(plugin_name, PLUGIN_INFO, NULL, - &cyc_complexity_plugin_info); - register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, - &cyc_complexity_pass_info); - - return 0; -} -- cgit v1.2.3