OpenWrt – Blame information for rev 1
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1 | office | 1 | From: Arnd Bergmann <arnd@arndb.de> |
2 | Date: Tue, 19 Jun 2018 13:14:56 -0700 |
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3 | Subject: [PATCH] kbuild: add macro for controlling warnings to |
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4 | linux/compiler.h |
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5 | |||
6 | I have occasionally run into a situation where it would make sense to |
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7 | control a compiler warning from a source file rather than doing so from |
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8 | a Makefile using the $(cc-disable-warning, ...) or $(cc-option, ...) |
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9 | helpers. |
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10 | |||
11 | The approach here is similar to what glibc uses, using __diag() and |
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12 | related macros to encapsulate a _Pragma("GCC diagnostic ...") statement |
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13 | that gets turned into the respective "#pragma GCC diagnostic ..." by |
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14 | the preprocessor when the macro gets expanded. |
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15 | |||
16 | Like glibc, I also have an argument to pass the affected compiler |
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17 | version, but decided to actually evaluate that one. For now, this |
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18 | supports GCC_4_6, GCC_4_7, GCC_4_8, GCC_4_9, GCC_5, GCC_6, GCC_7, |
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19 | GCC_8 and GCC_9. Adding support for CLANG_5 and other interesting |
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20 | versions is straightforward here. GNU compilers starting with gcc-4.2 |
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21 | could support it in principle, but "#pragma GCC diagnostic push" |
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22 | was only added in gcc-4.6, so it seems simpler to not deal with those |
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23 | at all. The same versions show a large number of warnings already, |
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24 | so it seems easier to just leave it at that and not do a more |
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25 | fine-grained control for them. |
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26 | |||
27 | The use cases I found so far include: |
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28 | |||
29 | - turning off the gcc-8 -Wattribute-alias warning inside of the |
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30 | SYSCALL_DEFINEx() macro without having to do it globally. |
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31 | |||
32 | - Reducing the build time for a simple re-make after a change, |
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33 | once we move the warnings from ./Makefile and |
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34 | ./scripts/Makefile.extrawarn into linux/compiler.h |
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35 | |||
36 | - More control over the warnings based on other configurations, |
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37 | using preprocessor syntax instead of Makefile syntax. This should make |
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38 | it easier for the average developer to understand and change things. |
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39 | |||
40 | - Adding an easy way to turn the W=1 option on unconditionally |
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41 | for a subdirectory or a specific file. This has been requested |
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42 | by several developers in the past that want to have their subsystems |
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43 | W=1 clean. |
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44 | |||
45 | - Integrating clang better into the build systems. Clang supports |
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46 | more warnings than GCC, and we probably want to classify them |
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47 | as default, W=1, W=2 etc, but there are cases in which the |
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48 | warnings should be classified differently due to excessive false |
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49 | positives from one or the other compiler. |
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50 | |||
51 | - Adding a way to turn the default warnings into errors (e.g. using |
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52 | a new "make E=0" tag) while not also turning the W=1 warnings into |
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53 | errors. |
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54 | |||
55 | This patch for now just adds the minimal infrastructure in order to |
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56 | do the first of the list above. As the #pragma GCC diagnostic |
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57 | takes precedence over command line options, the next step would be |
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58 | to convert a lot of the individual Makefiles that set nonstandard |
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59 | options to use __diag() instead. |
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60 | |||
61 | [paul.burton@mips.com: |
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62 | - Rebase atop current master. |
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63 | - Add __diag_GCC, or more generally __diag_<compiler>, abstraction to |
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64 | avoid code outside of linux/compiler-gcc.h needing to duplicate |
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65 | knowledge about different GCC versions. |
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66 | - Add a comment argument to __diag_{ignore,warn,error} which isn't |
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67 | used in the expansion of the macros but serves to push people to |
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68 | document the reason for using them - per feedback from Kees Cook. |
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69 | - Translate severity to GCC-specific pragmas in linux/compiler-gcc.h |
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70 | rather than using GCC-specific in linux/compiler_types.h. |
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71 | - Drop all but GCC 8 macros, since we only need to define macros for |
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72 | versions that we need to introduce pragmas for, and as of this |
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73 | series that's just GCC 8. |
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74 | - Capitalize comments in linux/compiler-gcc.h to match the style of |
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75 | the rest of the file. |
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76 | - Line up macro definitions with tabs in linux/compiler-gcc.h.] |
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77 | |||
78 | Signed-off-by: Arnd Bergmann <arnd@arndb.de> |
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79 | Signed-off-by: Paul Burton <paul.burton@mips.com> |
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80 | Tested-by: Christophe Leroy <christophe.leroy@c-s.fr> |
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81 | Tested-by: Stafford Horne <shorne@gmail.com> |
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82 | Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> |
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83 | --- |
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84 | |||
85 | --- a/include/linux/compiler-gcc.h |
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86 | +++ b/include/linux/compiler-gcc.h |
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87 | @@ -362,3 +362,30 @@ |
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88 | #if GCC_VERSION >= 50100 |
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89 | #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 |
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90 | #endif |
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91 | + |
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92 | + |
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93 | +/* |
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94 | + * Turn individual warnings and errors on and off locally, depending |
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95 | + * on version. |
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96 | + */ |
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97 | +#define __diag_GCC(version, severity, s) \ |
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98 | + __diag_GCC_ ## version(__diag_GCC_ ## severity s) |
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99 | + |
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100 | +/* Severity used in pragma directives */ |
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101 | +#define __diag_GCC_ignore ignored |
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102 | +#define __diag_GCC_warn warning |
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103 | +#define __diag_GCC_error error |
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104 | + |
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105 | +/* Compilers before gcc-4.6 do not understand "#pragma GCC diagnostic push" */ |
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106 | +#if GCC_VERSION >= 40600 |
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107 | +#define __diag_str1(s) #s |
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108 | +#define __diag_str(s) __diag_str1(s) |
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109 | +#define __diag(s) _Pragma(__diag_str(GCC diagnostic s)) |
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110 | +#endif |
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111 | + |
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112 | +#if GCC_VERSION >= 80000 |
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113 | +#define __diag_GCC_8(s) __diag(s) |
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114 | +#else |
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115 | +#define __diag_GCC_8(s) |
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116 | +#endif |
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117 | + |
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118 | --- a/include/linux/compiler_types.h |
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119 | +++ b/include/linux/compiler_types.h |
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120 | @@ -283,4 +283,22 @@ struct ftrace_likely_data { |
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121 | # define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) |
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122 | #endif |
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123 | |||
124 | +#ifndef __diag |
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125 | +#define __diag(string) |
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126 | +#endif |
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127 | + |
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128 | +#ifndef __diag_GCC |
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129 | +#define __diag_GCC(version, severity, string) |
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130 | +#endif |
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131 | + |
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132 | +#define __diag_push() __diag(push) |
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133 | +#define __diag_pop() __diag(pop) |
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134 | + |
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135 | +#define __diag_ignore(compiler, version, option, comment) \ |
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136 | + __diag_ ## compiler(version, ignore, option) |
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137 | +#define __diag_warn(compiler, version, option, comment) \ |
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138 | + __diag_ ## compiler(version, warn, option) |
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139 | +#define __diag_error(compiler, version, option, comment) \ |
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140 | + __diag_ ## compiler(version, error, option) |
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141 | + |
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142 | #endif /* __LINUX_COMPILER_TYPES_H */ |