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@@ -0,0 +1,140 @@
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+From: Arnd Bergmann <[email protected]>
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+Date: Tue, 19 Jun 2018 13:14:56 -0700
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+Subject: [PATCH] kbuild: add macro for controlling warnings to
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+ linux/compiler.h
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+
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+I have occasionally run into a situation where it would make sense to
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+control a compiler warning from a source file rather than doing so from
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+a Makefile using the $(cc-disable-warning, ...) or $(cc-option, ...)
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+helpers.
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+
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+The approach here is similar to what glibc uses, using __diag() and
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+related macros to encapsulate a _Pragma("GCC diagnostic ...") statement
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+that gets turned into the respective "#pragma GCC diagnostic ..." by
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+the preprocessor when the macro gets expanded.
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+
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+Like glibc, I also have an argument to pass the affected compiler
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+version, but decided to actually evaluate that one. For now, this
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+supports GCC_4_6, GCC_4_7, GCC_4_8, GCC_4_9, GCC_5, GCC_6, GCC_7,
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+GCC_8 and GCC_9. Adding support for CLANG_5 and other interesting
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+versions is straightforward here. GNU compilers starting with gcc-4.2
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+could support it in principle, but "#pragma GCC diagnostic push"
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+was only added in gcc-4.6, so it seems simpler to not deal with those
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+at all. The same versions show a large number of warnings already,
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+so it seems easier to just leave it at that and not do a more
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+fine-grained control for them.
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+
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+The use cases I found so far include:
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+
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+- turning off the gcc-8 -Wattribute-alias warning inside of the
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+ SYSCALL_DEFINEx() macro without having to do it globally.
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+
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+- Reducing the build time for a simple re-make after a change,
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+ once we move the warnings from ./Makefile and
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+ ./scripts/Makefile.extrawarn into linux/compiler.h
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+
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+- More control over the warnings based on other configurations,
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+ using preprocessor syntax instead of Makefile syntax. This should make
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+ it easier for the average developer to understand and change things.
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+
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+- Adding an easy way to turn the W=1 option on unconditionally
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+ for a subdirectory or a specific file. This has been requested
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+ by several developers in the past that want to have their subsystems
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+ W=1 clean.
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+
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+- Integrating clang better into the build systems. Clang supports
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+ more warnings than GCC, and we probably want to classify them
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+ as default, W=1, W=2 etc, but there are cases in which the
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+ warnings should be classified differently due to excessive false
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+ positives from one or the other compiler.
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+
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+- Adding a way to turn the default warnings into errors (e.g. using
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+ a new "make E=0" tag) while not also turning the W=1 warnings into
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+ errors.
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+
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+This patch for now just adds the minimal infrastructure in order to
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+do the first of the list above. As the #pragma GCC diagnostic
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+takes precedence over command line options, the next step would be
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+to convert a lot of the individual Makefiles that set nonstandard
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+options to use __diag() instead.
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+
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+[[email protected]:
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+ - Rebase atop current master.
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+ - Add __diag_GCC, or more generally __diag_<compiler>, abstraction to
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+ avoid code outside of linux/compiler-gcc.h needing to duplicate
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+ knowledge about different GCC versions.
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+ - Add a comment argument to __diag_{ignore,warn,error} which isn't
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+ used in the expansion of the macros but serves to push people to
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+ document the reason for using them - per feedback from Kees Cook.
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+ - Translate severity to GCC-specific pragmas in linux/compiler-gcc.h
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+ rather than using GCC-specific in linux/compiler_types.h.
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+ - Drop all but GCC 8 macros, since we only need to define macros for
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+ versions that we need to introduce pragmas for, and as of this
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+ series that's just GCC 8.
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+ - Capitalize comments in linux/compiler-gcc.h to match the style of
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+ the rest of the file.
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+ - Line up macro definitions with tabs in linux/compiler-gcc.h.]
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+
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+Signed-off-by: Arnd Bergmann <[email protected]>
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+Signed-off-by: Paul Burton <[email protected]>
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+Tested-by: Christophe Leroy <[email protected]>
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+Tested-by: Stafford Horne <[email protected]>
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+Signed-off-by: Masahiro Yamada <[email protected]>
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+---
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+
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+--- a/include/linux/compiler-gcc.h
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++++ b/include/linux/compiler-gcc.h
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+@@ -343,3 +343,28 @@
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+ * code
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+ */
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+ #define uninitialized_var(x) x = x
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++
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++/*
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++ * Turn individual warnings and errors on and off locally, depending
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++ * on version.
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++ */
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++#define __diag_GCC(version, severity, s) \
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++ __diag_GCC_ ## version(__diag_GCC_ ## severity s)
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++
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++/* Severity used in pragma directives */
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++#define __diag_GCC_ignore ignored
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++#define __diag_GCC_warn warning
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++#define __diag_GCC_error error
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++
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++/* Compilers before gcc-4.6 do not understand "#pragma GCC diagnostic push" */
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++#if GCC_VERSION >= 40600
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++#define __diag_str1(s) #s
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++#define __diag_str(s) __diag_str1(s)
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++#define __diag(s) _Pragma(__diag_str(GCC diagnostic s))
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++#endif
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++
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++#if GCC_VERSION >= 80000
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++#define __diag_GCC_8(s) __diag(s)
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++#else
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++#define __diag_GCC_8(s)
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++#endif
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+--- a/include/linux/compiler_types.h
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++++ b/include/linux/compiler_types.h
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+@@ -271,4 +271,22 @@ struct ftrace_likely_data {
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+ # define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
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+ #endif
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+
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++#ifndef __diag
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++#define __diag(string)
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++#endif
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++
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++#ifndef __diag_GCC
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++#define __diag_GCC(version, severity, string)
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++#endif
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++
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++#define __diag_push() __diag(push)
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++#define __diag_pop() __diag(pop)
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++
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++#define __diag_ignore(compiler, version, option, comment) \
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++ __diag_ ## compiler(version, ignore, option)
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++#define __diag_warn(compiler, version, option, comment) \
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++ __diag_ ## compiler(version, warn, option)
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++#define __diag_error(compiler, version, option, comment) \
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++ __diag_ ## compiler(version, error, option)
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++
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+ #endif /* __LINUX_COMPILER_TYPES_H */
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Felix Fietkau