target/linux/generic/backport-4.9/012-kbuild-add-macro-for-controlling-warnings-to-linux-c.patch

   1 From: Arnd Bergmann <arnd@arndb.de>
   2 Date: Tue, 19 Jun 2018 13:14:56 -0700
   3 Subject: [PATCH] kbuild: add macro for controlling warnings to
   4  linux/compiler.h
   5
   6 I have occasionally run into a situation where it would make sense to
   7 control a compiler warning from a source file rather than doing so from
   8 a Makefile using the $(cc-disable-warning, ...) or $(cc-option, ...)
   9 helpers.
  10
  11 The approach here is similar to what glibc uses, using __diag() and
  12 related macros to encapsulate a _Pragma("GCC diagnostic ...") statement
  13 that gets turned into the respective "#pragma GCC diagnostic ..." by
  14 the preprocessor when the macro gets expanded.
  15
  16 Like glibc, I also have an argument to pass the affected compiler
  17 version, but decided to actually evaluate that one. For now, this
  18 supports GCC_4_6, GCC_4_7, GCC_4_8, GCC_4_9, GCC_5, GCC_6, GCC_7,
  19 GCC_8 and GCC_9. Adding support for CLANG_5 and other interesting
  20 versions is straightforward here. GNU compilers starting with gcc-4.2
  21 could support it in principle, but "#pragma GCC diagnostic push"
  22 was only added in gcc-4.6, so it seems simpler to not deal with those
  23 at all. The same versions show a large number of warnings already,
  24 so it seems easier to just leave it at that and not do a more
  25 fine-grained control for them.
  26
  27 The use cases I found so far include:
  28
  29 - turning off the gcc-8 -Wattribute-alias warning inside of the
  30   SYSCALL_DEFINEx() macro without having to do it globally.
  31
  32 - Reducing the build time for a simple re-make after a change,
  33   once we move the warnings from ./Makefile and
  34   ./scripts/Makefile.extrawarn into linux/compiler.h
  35
  36 - More control over the warnings based on other configurations,
  37   using preprocessor syntax instead of Makefile syntax. This should make
  38   it easier for the average developer to understand and change things.
  39
  40 - Adding an easy way to turn the W=1 option on unconditionally
  41   for a subdirectory or a specific file. This has been requested
  42   by several developers in the past that want to have their subsystems
  43   W=1 clean.
  44
  45 - Integrating clang better into the build systems. Clang supports
  46   more warnings than GCC, and we probably want to classify them
  47   as default, W=1, W=2 etc, but there are cases in which the
  48   warnings should be classified differently due to excessive false
  49   positives from one or the other compiler.
  50
  51 - Adding a way to turn the default warnings into errors (e.g. using
  52   a new "make E=0" tag) while not also turning the W=1 warnings into
  53   errors.
  54
  55 This patch for now just adds the minimal infrastructure in order to
  56 do the first of the list above. As the #pragma GCC diagnostic
  57 takes precedence over command line options, the next step would be
  58 to convert a lot of the individual Makefiles that set nonstandard
  59 options to use __diag() instead.
  60
  61 [paul.burton@mips.com:
  62   - Rebase atop current master.
  63   - Add __diag_GCC, or more generally __diag_<compiler>, abstraction to
  64     avoid code outside of linux/compiler-gcc.h needing to duplicate
  65     knowledge about different GCC versions.
  66   - Add a comment argument to __diag_{ignore,warn,error} which isn't
  67     used in the expansion of the macros but serves to push people to
  68     document the reason for using them - per feedback from Kees Cook.
  69   - Translate severity to GCC-specific pragmas in linux/compiler-gcc.h
  70     rather than using GCC-specific in linux/compiler_types.h.
  71   - Drop all but GCC 8 macros, since we only need to define macros for
  72     versions that we need to introduce pragmas for, and as of this
  73     series that's just GCC 8.
  74   - Capitalize comments in linux/compiler-gcc.h to match the style of
  75     the rest of the file.
  76   - Line up macro definitions with tabs in linux/compiler-gcc.h.]
  77
  78 Signed-off-by: Arnd Bergmann <arnd@arndb.de>
  79 Signed-off-by: Paul Burton <paul.burton@mips.com>
  80 Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>
  81 Tested-by: Stafford Horne <shorne@gmail.com>
  82 Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
  83 ---
  84
  85 --- a/include/linux/compiler-gcc.h
  86 +++ b/include/linux/compiler-gcc.h
  87 @@ -338,3 +338,30 @@
  88  #if GCC_VERSION >= 50100
  89  #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
  90  #endif
  91 +
  92 +
  93 +/*
  94 + * Turn individual warnings and errors on and off locally, depending
  95 + * on version.
  96 + */
  97 +#define __diag_GCC(version, severity, s) \
  98 +       __diag_GCC_ ## version(__diag_GCC_ ## severity s)
  99 +
 100 +/* Severity used in pragma directives */
 101 +#define __diag_GCC_ignore      ignored
 102 +#define __diag_GCC_warn                warning
 103 +#define __diag_GCC_error       error
 104 +
 105 +/* Compilers before gcc-4.6 do not understand "#pragma GCC diagnostic push" */
 106 +#if GCC_VERSION >= 40600
 107 +#define __diag_str1(s)         #s
 108 +#define __diag_str(s)          __diag_str1(s)
 109 +#define __diag(s)              _Pragma(__diag_str(GCC diagnostic s))
 110 +#endif
 111 +
 112 +#if GCC_VERSION >= 80000
 113 +#define __diag_GCC_8(s)                __diag(s)
 114 +#else
 115 +#define __diag_GCC_8(s)
 116 +#endif
 117 +
 118 --- a/include/linux/compiler.h
 119 +++ b/include/linux/compiler.h
 120 @@ -578,4 +578,23 @@ static __always_inline void __write_once
 121  # define __kprobes
 122  # define nokprobe_inline       inline
 123  #endif
 124 +
 125 +#ifndef __diag
 126 +#define __diag(string)
 127 +#endif
 128 +
 129 +#ifndef __diag_GCC
 130 +#define __diag_GCC(version, severity, string)
 131 +#endif
 132 +
 133 +#define __diag_push()  __diag(push)
 134 +#define __diag_pop()   __diag(pop)
 135 +
 136 +#define __diag_ignore(compiler, version, option, comment) \
 137 +       __diag_ ## compiler(version, ignore, option)
 138 +#define __diag_warn(compiler, version, option, comment) \
 139 +       __diag_ ## compiler(version, warn, option)
 140 +#define __diag_error(compiler, version, option, comment) \
 141 +       __diag_ ## compiler(version, error, option)
 142 +
 143  #endif /* __LINUX_COMPILER_H */