sparse(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | WARNING OPTIONS | MISC OPTIONS | DEBUG OPTIONS | OTHER OPTIONS | SEE ALSO | HOMEPAGE | MAILING LIST | CONTRIBUTING AND REPORTING BUGS | DOCUMENTATION | AUTHORS | COLOPHON

sparse(1)                  General Commands Manual                 sparse(1)

NAME         top

       sparse - Semantic Parser for C

SYNOPSIS         top

       sparse [WARNING OPTIONS]... file.c

DESCRIPTION         top

       Sparse parses C source and looks for errors, producing warnings on
       standard error.

       Sparse accepts options controlling the set of warnings to generate.
       To turn on warnings Sparse does not issue by default, use the
       corresponding warning option -Wsomething.  Sparse issues some
       warnings by default; to turn off those warnings, pass the negation of
       the associated warning option, -Wno-something.

WARNING OPTIONS         top

       -fmax-warnings=COUNT
              Set the maximum number of displayed warnings to COUNT, which
              should be a numerical value or 'unlimited'.  The default limit
              is 100.

       -Wsparse-all
              Turn on all sparse warnings, except for those explicitly
              disabled via -Wno-something.

       -Wsparse-error
              Turn all sparse warnings into errors.

       -Waddress-space
              Warn about code which mixes pointers to different address
              spaces.

              Sparse allows an extended attribute
              __attribute__((address_space(id))) on pointers, which
              designates a pointer target in address space id (an identifier
              or a constant integer).  With -Waddress-space, Sparse treats
              pointers with identical target types but different address
              spaces as distinct types and will warn accordingly.

              Sparse will also warn on casts which remove the address space
              (casts to an integer type or to a plain pointer type). An
              exception to this is when the destination type is uintptr_t
              (or unsigned long) since such casts are often used to "get a
              pointer value representation in an integer type" and such
              values are independent of the address space.

              To override these warnings, use a type that includes
              __attribute__((force)).

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-address-space.

       -Wbitwise
              Warn about unsupported operations or type mismatches with
              restricted integer types.

              Sparse supports an extended attribute,
              __attribute__((bitwise)), which creates a new restricted
              integer type from a base integer type, distinct from the base
              integer type and from any other restricted integer type not
              declared in the same declaration or typedef.  For example,
              this allows programs to create typedefs for integer types with
              specific endianness.  With -Wbitwise, Sparse will warn on any
              use of a restricted type in arithmetic operations other than
              bitwise operations, and on any conversion of one restricted
              type into another, except via a cast that includes
              __attribute__((force)).

              __bitwise ends up being a "stronger integer separation", one
              that doesn't allow you to mix with non-bitwise integers, so
              now it's much harder to lose the type by mistake.

              __bitwise is for *unique types* that cannot be mixed with
              other types, and that you'd never want to just use as a random
              integer (the integer 0 is special, though, and gets silently
              accepted iirc - it's kind of like "NULL" for pointers). So
              "gfp_t" or the "safe endianness" types would be __bitwise: you
              can only operate on them by doing specific operations that
              know about *that* particular type.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-bitwise.

       -Wbitwise-pointer
              Same as -Wbitwise but for casts to or from pointers to bitwise
              types.

              Sparse does not issue these warnings by default.

       -Wcast-from-as
              Warn about casts which remove an address space from a pointer
              type.

              This is similar to -Waddress-space but will also warn on casts
              to unsigned long.

              Sparse does not issues these warnings by default.

       -Wcast-to-as
              Warn about casts which add an address space to a pointer type.

              A cast that includes __attribute__((force)) will suppress this
              warning.  No warning is generated if the original type is
              uintptr_t (or unsigned long).

              Sparse does not issue these warnings by default.

       -Wcast-truncate
              Warn about casts that truncate constant values.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-cast-truncate.

       -Wconstant-suffix
              Warn if an integer constant is larger than the maximum
              representable value of the type indicated by its type suffix
              (if any). For example, on a system where ints are 32-bit and
              longs 64-bit, the constant 0x100000000U is larger than can be
              represented by an unsigned int but fits in an unsigned long.
              So its type is unsigned long but this is not indicated by its
              suffix. In this case, the warning could be suppressed by using
              the suffix UL: 0x100000000UL.

              Sparse does not issue these warnings by default.

       -Wconstexpr-not-const
              Warn if a non-constant expression is encountered when really
              expecting a constant expression instead.  Currently, this
              warns when initializing an object of static storage duration
              with an initializer which is not a constant expression.

              Sparse does not issue these warnings by default.

       -Wcontext
              Warn about potential errors in synchronization or other
              delimited contexts.

              Sparse supports several means of designating functions or
              statements that delimit contexts, such as synchronization.
              Functions with the extended attribute
              __attribute__((context(expression,in_context,out_context))
              require the context expression (for instance, a lock) to have
              the value in_context (a constant nonnegative integer) when
              called, and return with the value out_context (a constant
              nonnegative integer).  For APIs defined via macros, use the
              statement form __context__(expression,in_value,out_value) in
              the body of the macro.

              With -Wcontext Sparse will warn when it sees a function change
              the context without indicating this with a context attribute,
              either by decreasing a context below zero (such as by
              releasing a lock without acquiring it), or returning with a
              changed context (such as by acquiring a lock without releasing
              it).  Sparse will also warn about blocks of code which may
              potentially execute with different contexts.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-context.

       -Wdecl Warn about any non-static variable or function definition that
              has no previous declaration.

              Private symbols (functions and variables) internal to a given
              source file should use static, to allow additional compiler
              optimizations, allow detection of unused symbols, and prevent
              other code from relying on these internal symbols.  Public
              symbols used by other source files will need declarations
              visible to those other source files, such as in a header file.
              All declarations should fall into one of these two categories.
              Thus, with -Wdecl, Sparse warns about any symbol definition
              with neither static nor a declaration.  To fix this warning,
              declare private symbols static, and ensure that the files
              defining public symbols have the symbol declarations available
              first (such as by including the appropriate header file).

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-decl.

       -Wdeclaration-after-statement
              Warn about declarations that are not at the start of a block.

              These declarations are permitted in C99 but not in C89.

              Sparse issues these warnings by default only when the C
              dialect is C89 (i.e. -ansi or -std=c89).  To turn them off,
              use -Wno-declaration-after-statement.

       -Wdefault-bitfield-sign
              Warn about any bitfield with no explicit signedness.

              Bitfields have no standard-specified default signedness. (C99
              6.7.2) A bitfield without an explicit signed or unsigned
              creates a portability problem for software that relies on the
              available range of values.  To fix this, specify the bitfield
              type as signed or unsigned explicitly.

              Sparse does not issue these warnings by default.

       -Wdesignated-init
              Warn about positional initialization of structs marked as
              requiring designated initializers.

              Sparse allows an attribute __attribute__((designated_init))
              which marks a struct as requiring designated initializers.
              Sparse will warn about positional initialization of a struct
              variable or struct literal of a type that has this attribute.

              Requiring designated initializers for a particular struct type
              will insulate code using that struct type from changes to the
              layout of the type, avoiding the need to change initializers
              for that type unless they initialize a removed or incompatibly
              changed field.

              Common examples of this type of struct include collections of
              function pointers for the implementations of a class of
              related operations, for which the default NULL for an
              unmentioned field in a designated initializer will correctly
              indicate the absence of that operation.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-designated-init.

       -Wdo-while
              Warn about do-while loops that do not delimit the loop body
              with braces.

              Sparse does not issue these warnings by default.

       -Wenum-mismatch
              Warn about the use of an expression of an incorrect enum type
              when initializing another enum type, assigning to another enum
              type, or passing an argument to a function which expects
              another enum type.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-enum-mismatch.

       -Wexternal-function-has-definition
              Warn about function definitions that are declared with
              external linkage.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-external-function-has-definition.

       -Winit-cstring
              Warn about initialization of a char array with a too long
              constant C string.

              If the size of the char array and the length of the string are
              the same, there is no space for the last nul char of the
              string in the array:

              char s[3] = "abc";

              If the array is used as a byte array, not as C string, this
              warning is just noise. However, if the array is passed to
              functions dealing with C string like printf(%s) and strcmp, it
              may cause a trouble.

              Sparse does not issue these warnings by default.

       -Wmemcpy-max-count
              Warn about call of memcpy(), memset(), copy_from_user(), or
              copy_to_user() with a large compile-time byte count.

              Sparse issues these warnings by default. To turn them off, use
              -Wno-memcpy-max-count.

              The limit can be changed with -fmemcpy-max-count=COUNT, the
              default being 100000.

       -Wnewline-eof
              Warn if the input file doesn't end with a newline.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-newline-eof.

       -Wnon-pointer-null
              Warn about the use of 0 as a NULL pointer.

              0 has integer type.  NULL has pointer type.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-non-pointer-null.

       -Wold-initializer
              Warn about the use of the pre-C99 GCC syntax for designated
              initializers.

              C99 provides a standard syntax for designated fields in struct
              or union initializers:

              struct structname var = { .field = value };

              GCC also has an old, non-standard syntax for designated
              initializers which predates C99:

              struct structname var = { field: value };

              Sparse will warn about the use of GCC's non-standard syntax
              for designated initializers.  To fix this warning, convert
              designated initializers to use the standard C99 syntax.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-old-initializer.

       -Wone-bit-signed-bitfield
              Warn about any one-bit signed bitfields.

              A one-bit signed bitfield can only have the values 0 and -1,
              or with some compilers only 0; this results in unexpected
              behavior for programs which expected the ability to store 0
              and 1.

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-one-bit-signed-bitfield.

       -Wparen-string
              Warn about the use of a parenthesized string to initialize an
              array.

              Standard C syntax does not permit a parenthesized string as an
              array initializer.  GCC allows this syntax as an extension.
              With -Wparen-string, Sparse will warn about this syntax.

              Sparse does not issue these warnings by default.

       -Wpointer-arith
              Warn about anything that depends on the sizeof a void or
              function type.

              C99 does not allow the sizeof operator to be applied to
              function types or to incomplete types such as void. GCC allows
              sizeof to be applied to these types as an extension and
              assigns these types a size of 1. With -pointer-arith, Sparse
              will warn about pointer arithmetic on void or function
              pointers, as well as expressions which directly apply the
              sizeof operator to void or function types.

              Sparse does not issue these warnings by default.

       -Wptr-subtraction-blows
              Warn when subtracting two pointers to a type with a non-power-
              of-two size.

              Subtracting two pointers to a given type gives a difference in
              terms of the number of items of that type.  To generate this
              value, compilers will usually need to divide the difference by
              the size of the type, an potentially expensive operation for
              sizes other than powers of two.

              Code written using pointer subtraction can often use another
              approach instead, such as array indexing with an explicit
              array index variable, which may allow compilers to generate
              more efficient code.

              Sparse does not issue these warnings by default.

       -Wreturn-void
              Warn if a function with return type void returns a void
              expression.

              C99 permits this, and in some cases this allows for more
              generic code in macros that use typeof or take a type as a
              macro argument.  However, some programs consider this poor
              style, and those programs can use -Wreturn-void to get
              warnings about it.

              Sparse does not issue these warnings by default.

       -Wshadow
              Warn when declaring a symbol which shadows a declaration with
              the same name in an outer scope.

              Such declarations can lead to error-prone code.

              Sparse does not issue these warnings by default.

       -Wshift-count-negative
              Warn if a shift count is negative.

              Sparse issues these warnings by default.

       -Wshift-count-overflow
              Warn if a shift count is bigger than the operand's width.

              Sparse issues these warnings by default.

       -Wsizeof-bool
              Warn when checking the sizeof a _Bool.

              C99 does not specify the size of a _Bool. GCC, by default,
              uses 1.

              Sparse does not issue these warnings by default.

       -Wtransparent-union
              Warn about any declaration using the GCC extension
              __attribute__((transparent_union)).

              Sparse issues these warnings by default.  To turn them off,
              use -Wno-transparent-union.

       -Wtypesign
              Warn when converting a pointer to an integer type into a
              pointer to an integer type with different signedness.

              Sparse does not issue these warnings by default.

       -Wundef
              Warn about preprocessor conditionals that use the value of an
              undefined preprocessor symbol.

              Standard C (C99 6.10.1) permits using the value of an
              undefined preprocessor symbol in preprocessor conditionals,
              and specifies it has a value of 0.  However, this behavior can
              lead to subtle errors.

              Sparse does not issue these warnings by default.

       -Wuniversal-initializer
              Do not suppress warnings caused by using '{ 0 }' instead of
              '{ }' on aggregate types, ignoring its special status as
              universal initializer.  The concerned warnings are, for
              example, those triggered by -Wdesignated-init or
              -Wnon-pointer-null.

              Sparse does not issue these warnings by default, processing
              '{ 0 }' the same as '{ }'.

MISC OPTIONS         top

       --arch=ARCH
              Specify the target architecture.  For architectures having
              both a 32-bit and a 64-bit variant (mips, powerpc, riscv and
              sparc) the architecture name can be suffixed with 32 or 64.

              The default architecture and size is the one of the machine
              used to build Sparse.

       -gcc-base-dir dir
              Look for compiler-provided system headers in dir/include/ and
              dir/include-fixed/.

       -multiarch-dir dir
              Look for system headers in the multiarch subdirectory dir.
              The dir name would normally take the form of the target's
              normalized GNU triplet. (e.g. i386-linux-gnu).

DEBUG OPTIONS         top

       -fmem-report
              Report some statistics about memory allocation used by the
              tool.

OTHER OPTIONS         top

       -fdiagnostic-prefix[=PREFIX]
              Prefix all diagnostics by the given PREFIX, followed by ": ".
              If no one is given "sparse" is used.  The default is to not
              use a prefix at all.

       -fmemcpy-max-count=COUNT
              Set the limit for the warnings given by -Wmemcpy-max-count.  A
              COUNT of 'unlimited' or '0' will effectively disable the
              warning.  The default limit is 100000.

       -ftabstop=WIDTH
              Set the distance between tab stops.  This helps sparse report
              correct column numbers in warnings or errors.  If the value is
              less than 1 or greater than 100, the option is ignored.  The
              default is 8.

       -f[no-]unsigned-char, -f[no-]signed-char
              Let plain 'char' be unsigned or signed.  By default chars are
              signed.

SEE ALSO         top

       cgcc(1)

HOMEPAGE         top

       http://www.kernel.org/pub/software/devel/sparse/

MAILING LIST         top

       linux-sparse@vger.kernel.org

CONTRIBUTING AND REPORTING BUGS         top

       Submission of patches and reporting of bugs, as well as discussions
       related to Sparse, should be done via the mailing list (linux-
       sparse@vger.kernel.org) where the development and maintenance is
       primarily done.  You do not have to be subscribed to the list to send
       a message there.

       Bugs can also be reported and tracked via the Linux kernel's
       bugzilla:
       http://bugzilla.kernel.org/enter_bug.cgi?component=Sparse&product=Tools
       .

DOCUMENTATION         top

       More documentation about Sparse can be found at
       https://sparse.docs.kernel.org

AUTHORS         top

       Sparse was started by Linus Torvalds.  The complete list of
       contributors can be find at
       https://www.openhub.net/p/sparse/contributors .

       Luc Van Oostenryck is Sparse's current maintainer.

COLOPHON         top

       This page is part of the sparse (a Semantic Parser for C) project.
       Information about the project can be found at 
       ⟨https://sparse.wiki.kernel.org/⟩.  If you have a bug report for this
       manual page, send it to linux-sparse@vger.kernel.org.  This page was
       obtained from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/devel/sparse/sparse.git⟩ on
       2020-07-14.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-07-13.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

                                                                   sparse(1)

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