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authorArnd Bergmann <arnd@arndb.de>2018-06-19 23:14:56 +0300
committerMasahiro Yamada <yamada.masahiro@socionext.com>2018-06-25 17:21:12 +0300
commit8793bb7f4a9dd1396575d2e9337d331662cb7555 (patch)
tree782e0fc99d35369747beb58e4aed8c0e1d462665 /include
parentce397d215ccd07b8ae3f71db689aedb85d56ab40 (diff)
downloadlinux-8793bb7f4a9dd1396575d2e9337d331662cb7555.tar.xz
kbuild: add macro for controlling warnings to linux/compiler.h
I have occasionally run into a situation where it would make sense to control a compiler warning from a source file rather than doing so from a Makefile using the $(cc-disable-warning, ...) or $(cc-option, ...) helpers. The approach here is similar to what glibc uses, using __diag() and related macros to encapsulate a _Pragma("GCC diagnostic ...") statement that gets turned into the respective "#pragma GCC diagnostic ..." by the preprocessor when the macro gets expanded. Like glibc, I also have an argument to pass the affected compiler version, but decided to actually evaluate that one. For now, this supports GCC_4_6, GCC_4_7, GCC_4_8, GCC_4_9, GCC_5, GCC_6, GCC_7, GCC_8 and GCC_9. Adding support for CLANG_5 and other interesting versions is straightforward here. GNU compilers starting with gcc-4.2 could support it in principle, but "#pragma GCC diagnostic push" was only added in gcc-4.6, so it seems simpler to not deal with those at all. The same versions show a large number of warnings already, so it seems easier to just leave it at that and not do a more fine-grained control for them. The use cases I found so far include: - turning off the gcc-8 -Wattribute-alias warning inside of the SYSCALL_DEFINEx() macro without having to do it globally. - Reducing the build time for a simple re-make after a change, once we move the warnings from ./Makefile and ./scripts/Makefile.extrawarn into linux/compiler.h - More control over the warnings based on other configurations, using preprocessor syntax instead of Makefile syntax. This should make it easier for the average developer to understand and change things. - Adding an easy way to turn the W=1 option on unconditionally for a subdirectory or a specific file. This has been requested by several developers in the past that want to have their subsystems W=1 clean. - Integrating clang better into the build systems. Clang supports more warnings than GCC, and we probably want to classify them as default, W=1, W=2 etc, but there are cases in which the warnings should be classified differently due to excessive false positives from one or the other compiler. - Adding a way to turn the default warnings into errors (e.g. using a new "make E=0" tag) while not also turning the W=1 warnings into errors. This patch for now just adds the minimal infrastructure in order to do the first of the list above. As the #pragma GCC diagnostic takes precedence over command line options, the next step would be to convert a lot of the individual Makefiles that set nonstandard options to use __diag() instead. [paul.burton@mips.com: - Rebase atop current master. - Add __diag_GCC, or more generally __diag_<compiler>, abstraction to avoid code outside of linux/compiler-gcc.h needing to duplicate knowledge about different GCC versions. - Add a comment argument to __diag_{ignore,warn,error} which isn't used in the expansion of the macros but serves to push people to document the reason for using them - per feedback from Kees Cook. - Translate severity to GCC-specific pragmas in linux/compiler-gcc.h rather than using GCC-specific in linux/compiler_types.h. - Drop all but GCC 8 macros, since we only need to define macros for versions that we need to introduce pragmas for, and as of this series that's just GCC 8. - Capitalize comments in linux/compiler-gcc.h to match the style of the rest of the file. - Line up macro definitions with tabs in linux/compiler-gcc.h.] Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Paul Burton <paul.burton@mips.com> Tested-by: Christophe Leroy <christophe.leroy@c-s.fr> Tested-by: Stafford Horne <shorne@gmail.com> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/compiler-gcc.h25
-rw-r--r--include/linux/compiler_types.h18
2 files changed, 43 insertions, 0 deletions
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index f1a7492a5cc8..fd282c7d3e5e 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -347,3 +347,28 @@
#if GCC_VERSION >= 50100
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
#endif
+
+/*
+ * Turn individual warnings and errors on and off locally, depending
+ * on version.
+ */
+#define __diag_GCC(version, severity, s) \
+ __diag_GCC_ ## version(__diag_GCC_ ## severity s)
+
+/* Severity used in pragma directives */
+#define __diag_GCC_ignore ignored
+#define __diag_GCC_warn warning
+#define __diag_GCC_error error
+
+/* Compilers before gcc-4.6 do not understand "#pragma GCC diagnostic push" */
+#if GCC_VERSION >= 40600
+#define __diag_str1(s) #s
+#define __diag_str(s) __diag_str1(s)
+#define __diag(s) _Pragma(__diag_str(GCC diagnostic s))
+#endif
+
+#if GCC_VERSION >= 80000
+#define __diag_GCC_8(s) __diag(s)
+#else
+#define __diag_GCC_8(s)
+#endif
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 6b79a9bba9a7..a8ba6b04152c 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -271,4 +271,22 @@ struct ftrace_likely_data {
# define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
#endif
+#ifndef __diag
+#define __diag(string)
+#endif
+
+#ifndef __diag_GCC
+#define __diag_GCC(version, severity, string)
+#endif
+
+#define __diag_push() __diag(push)
+#define __diag_pop() __diag(pop)
+
+#define __diag_ignore(compiler, version, option, comment) \
+ __diag_ ## compiler(version, ignore, option)
+#define __diag_warn(compiler, version, option, comment) \
+ __diag_ ## compiler(version, warn, option)
+#define __diag_error(compiler, version, option, comment) \
+ __diag_ ## compiler(version, error, option)
+
#endif /* __LINUX_COMPILER_TYPES_H */