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README-WARNINGS.md

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Compiler Warnings

The general recommendation is to try to compile with as many warnings checks enabled, and explicitly disable some warnings where needed.

Enabling all warnings for GCC is a bit more complicated, so the minimum recommended would be to pass the build with clang -Wall -Weverything.

GCC

From the GCC 10 manual:

-Wall

This option turns on the following warning flags:

  • -Waddress
  • -Warray-bounds=1 (only with ‘-O2’)
  • -Wbool-compare
  • -Wbool-operation
  • -Wc++11-compat
  • -Wc++14-compat
  • -Wcatch-value (C++ and Objective-C++ only)
  • -Wchar-subscripts
  • -Wcomment
  • -Wduplicate-decl-specifier (C and Objective-C only)
  • -Wenum-compare (in C/ObjC; this is on by default in C++)
  • -Wenum-conversion in C/ObjC;
  • -Wformat
  • -Wformat-overflow
  • -Wformat-truncation
  • -Wint-in-bool-context
  • -Wimplicit (C and Objective-C only)
  • -Wimplicit-int (C and Objective-C only)
  • -Wimplicit-function-declaration (C and Objective-C only)
  • -Winit-self (only for C++)
  • -Wlogical-not-parentheses
  • -Wmain (only for C/ObjC and unless ‘-ffreestanding’)
  • -Wmaybe-uninitialized
  • -Wmemset-elt-size
  • -Wmemset-transposed-args
  • -Wmisleading-indentation (only for C/C++)
  • -Wmissing-attributes
  • -Wmissing-braces (only for C/ObjC)
  • -Wmultistatement-macros
  • -Wnarrowing (only for C++)
  • -Wnonnull
  • -Wnonnull-compare
  • -Wopenmp-simd
  • -Wparentheses
  • -Wpessimizing-move (only for C++)
  • -Wpointer-sign
  • -Wreorder
  • -Wrestrict
  • -Wreturn-type
  • -Wsequence-point
  • -Wsign-compare (only in C++)
  • -Wsizeof-pointer-div
  • -Wsizeof-pointer-memaccess
  • -Wstrict-aliasing
  • -Wstrict-overflow=1
  • -Wswitch
  • -Wtautological-compare
  • -Wtrigraphs
  • -Wuninitialized
  • -Wunknown-pragmas
  • -Wunused-function
  • -Wunused-label
  • -Wunused-value
  • -Wunused-variable
  • -Wvolatile-register-var
  • -Wzero-length-bounds

-Wextra

This enables some extra warning flags that are not enabled by ‘-Wall’.

  • -Wclobbered
  • -Wcast-function-type
  • -Wdeprecated-copy (C++ only)
  • -Wempty-body
  • -Wignored-qualifiers
  • -Wimplicit-fallthrough=3 ((attribute ((fallthrough));))
  • -Wmissing-field-initializers
  • -Wmissing-parameter-type (C only)
  • -Wold-style-declaration (C only)
  • -Woverride-init
  • -Wsign-compare (C only)
  • -Wstring-compare
  • -Wredundant-move (only for C++)
  • -Wtype-limits
  • -Wuninitialized
  • -Wshift-negative-value (in C++03 and in C99 and newer)
  • -Wunused-parameter (only with ‘-Wunused’ or ‘-Wall’)
  • -Wunused-but-set-parameter (only with ‘-Wunused’ or ‘-Wall’)

Other

  • -Waggregate-return
  • -Warith-conversion <-- since 10.x
  • -Wbad-function-cast (C and Objective-C only)
  • -Wc++-compat (C and Objective-C only)
  • -Wcast-align
  • -Wcast-qual
  • -Wconversion
  • -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
  • -Wduplicate-decl-specifier (C and Objective-C only)
  • -Wduplicated-branches
  • -Wduplicated-cond
  • -Wfloat-conversion
  • -Wfloat-equal
  • -Wformat-nonliteral
  • -Wformat-overflow=2
  • -Wformat-security
  • -Wformat-signedness
  • -Wformat-truncation=2
  • -Wformat-y2k
  • -Wformat=2
  • -Wlogical-op
  • -Wmissing-declarations
  • -Wmissing-include-dirs
  • -Wmissing-prototypes (C and Objective-C only)
  • -Wnested-externs (C and Objective-C only)
  • -Wnull-dereference
  • -Wold-style-definition
  • -Wpacked
  • -Wpadded
  • -Wpointer-arith
  • -Wredundant-decls
  • -Wshadow
  • -Wshift-overflow=2
  • -Wsign-conversion
  • -Wstrict-prototypes (C and Objective-C only)
  • -Wswitch-default
  • -Wswitch-enum
  • -Wundef
  • -Wuninitialized
  • -Wvla

And for C++

  • -Wabi-tag (C++ and Objective-C++ only) <- too noisy
  • -Wcomma-subscript (C++ and Objective-C++ only) <-- since 10.x
  • -Wctor-dtor-privacy (C++ and Objective-C++ only)
  • -Wextra-semi (C++, Objective-C++ only)
  • -Wmismatched-tags (C++ and Objective-C++ only) <-- since 10.x, fails on 10.1
  • -Wnoexcept (C++ and Objective-C++ only)
  • -Wnon-virtual-dtor (C++ and Objective-C++ only)
  • -Wold-style-cast (C++ and Objective-C++ only)
  • -Woverloaded-virtual (C++ and Objective-C++ only)
  • -Wplacement-new=2 (C++, Objective-C++ only)
  • -Wredundant-tags (C++ and Objective-C++ only) <-- since 10.x
  • -Wregister (C++ and Objective-C++ only)
  • -Wsign-promo (C++ and Objective-C++ only)
  • -Wstrict-null-sentinel (C++ and Objective-C++ only)
  • -Wsuggest-final-methods
  • -Wsuggest-final-types
  • -Wsuggest-override
  • -Wuseless-cast (C++ and Objective-C++ only)
  • -Wvolatile (C++ and Objective-C++ only) <-- since 10.x
  • -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)

-Wpedantic

Do not enable it, since it'll complain about #include_next.

-Wmismatched-tags

On RISC-V 10.1 it fails with note: replace the class-key with 'struct' in system headers.

Silencing GCC warnings

Silencing GCC warnings is strightforward:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"

#pragma GCC diagnostic pop

There are a few GCC specific warnings, that are not accepted by clang, for example:

#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic ignored "-Wuseless-cast"
#pragma GCC diagnostic ignored "-Wsuggest-final-types"
#pragma GCC diagnostic ignored "-Wsuggest-final-methods"
#if __GNUC__ >= 10
#pragma GCC diagnostic ignored "-Wredundant-tags"
#endif
#endif

For header files included in both C and C++ sources, it might be necessary to disable the -Wold-style-cast warning:

#pragma GCC diagnostic push

#if defined(__cplusplus)
#pragma GCC diagnostic ignored "-Wold-style-cast"
#endif

#pragma GCC diagnostic pop

Other warnings:

#pragma GCC diagnostic ignored "-Wpedantic"

GCC predefined macros

clang

For clang things are easier, to enable all possible checks use:

  • -Wall
  • -Weverything (includes -pedantic)
  • -Werror

Silencing clang warnings

There are many common warnings with GCC, and silencing them with #pragma GCC is ok, but there are several clang specific warnings, that need conditional compiling like:

#pragma GCC diagnostic push

#if defined(__clang__)
#pragma clang diagnostic ignored "-Wc++98-compat"
#endif

#pragma GCC diagnostic pop

Other warnings:

#pragma clang diagnostic ignored "-Wc++98-compat-pedantic"
#pragma clang diagnostic ignored "-Wglobal-constructors"
#pragma clang diagnostic ignored "-Wunused-macros"
#pragma clang diagnostic ignored "-Wempty-translation-unit"
#pragma clang diagnostic ignored "-Wdeprecated-volatile"