gcc/doc/options.texi

@c Copyright (C) 2003-2021 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@node Options
@chapter Option specification files
@cindex option specification files
@cindex @samp{optc-gen.awk}

Most GCC command-line options are described by special option
definition files, the names of which conventionally end in
@code{.opt}.  This chapter describes the format of these files.

@menu
* Option file format::   The general layout of the files
* Option properties::    Supported option properties
@end menu

@node Option file format
@section Option file format

Option files are a simple list of records in which each field occupies
its own line and in which the records themselves are separated by
blank lines.  Comments may appear on their own line anywhere within
the file and are preceded by semicolons.  Whitespace is allowed before
the semicolon.

The files can contain the following types of record:

@itemize @bullet
@item
A language definition record.  These records have two fields: the
string @samp{Language} and the name of the language.  Once a language
has been declared in this way, it can be used as an option property.
@xref{Option properties}.

@item
A target specific save record to save additional information. These
records have two fields: the string @samp{TargetSave}, and a
declaration type to go in the @code{cl_target_option} structure.

@item
A variable record to define a variable used to store option
information.  These records have two fields: the string
@samp{Variable}, and a declaration of the type and name of the
variable, optionally with an initializer (but without any trailing
@samp{;}).  These records may be used for variables used for many
options where declaring the initializer in a single option definition
record, or duplicating it in many records, would be inappropriate, or
for variables set in option handlers rather than referenced by
@code{Var} properties.

@item
A variable record to define a variable used to store option
information.  These records have two fields: the string
@samp{TargetVariable}, and a declaration of the type and name of the
variable, optionally with an initializer (but without any trailing
@samp{;}).  @samp{TargetVariable} is a combination of @samp{Variable}
and @samp{TargetSave} records in that the variable is defined in the
@code{gcc_options} structure, but these variables are also stored in
the @code{cl_target_option} structure.  The variables are saved in the
target save code and restored in the target restore code.

@item
A variable record to record any additional files that the
@file{options.h} file should include.  This is useful to provide
enumeration or structure definitions needed for target variables.
These records have two fields: the string @samp{HeaderInclude} and the
name of the include file.

@item
A variable record to record any additional files that the
@file{options.c} or @file{options-save.c} file should include.  This
is useful to provide
inline functions needed for target variables and/or @code{#ifdef}
sequences to properly set up the initialization.  These records have
two fields: the string @samp{SourceInclude} and the name of the
include file.

@item
An enumeration record to define a set of strings that may be used as
arguments to an option or options.  These records have three fields:
the string @samp{Enum}, a space-separated list of properties and help
text used to describe the set of strings in @option{--help} output.
Properties use the same format as option properties; the following are
valid:
@table @code
@item Name(@var{name})
This property is required; @var{name} must be a name (suitable for use
in C identifiers) used to identify the set of strings in @code{Enum}
option properties.

@item Type(@var{type})
This property is required; @var{type} is the C type for variables set
by options using this enumeration together with @code{Var}.

@item UnknownError(@var{message})
The message @var{message} will be used as an error message if the
argument is invalid; for enumerations without @code{UnknownError}, a
generic error message is used.  @var{message} should contain a single
@samp{%qs} format, which will be used to format the invalid argument.
@end table

@item
An enumeration value record to define one of the strings in a set
given in an @samp{Enum} record.  These records have two fields: the
string @samp{EnumValue} and a space-separated list of properties.
Properties use the same format as option properties; the following are
valid:
@table @code
@item Enum(@var{name})
This property is required; @var{name} says which @samp{Enum} record
this @samp{EnumValue} record corresponds to.

@item String(@var{string})
This property is required; @var{string} is the string option argument
being described by this record.

@item Value(@var{value})
This property is required; it says what value (representable as
@code{int}) should be used for the given string.

@item Canonical
This property is optional.  If present, it says the present string is
the canonical one among all those with the given value.  Other strings
yielding that value will be mapped to this one so specs do not need to
handle them.

@item DriverOnly
This property is optional.  If present, the present string will only
be accepted by the driver.  This is used for cases such as
@option{-march=native} that are processed by the driver so that
@samp{gcc -v} shows how the options chosen depended on the system on
which the compiler was run.
@end table

@item
An option definition record.  These records have the following fields:
@enumerate
@item
the name of the option, with the leading ``-'' removed
@item
a space-separated list of option properties (@pxref{Option properties})
@item
the help text to use for @option{--help} (omitted if the second field
contains the @code{Undocumented} property).
@end enumerate

By default, all options beginning with ``f'', ``W'' or ``m'' are
implicitly assumed to take a ``no-'' form.  This form should not be
listed separately.  If an option beginning with one of these letters
does not have a ``no-'' form, you can use the @code{RejectNegative}
property to reject it.

The help text is automatically line-wrapped before being displayed.
Normally the name of the option is printed on the left-hand side of
the output and the help text is printed on the right.  However, if the
help text contains a tab character, the text to the left of the tab is
used instead of the option's name and the text to the right of the
tab forms the help text.  This allows you to elaborate on what type
of argument the option takes.

@item
A target mask record.  These records have one field of the form
@samp{Mask(@var{x})}.  The options-processing script will automatically
allocate a bit in @code{target_flags} (@pxref{Run-time Target}) for
each mask name @var{x} and set the macro @code{MASK_@var{x}} to the
appropriate bitmask.  It will also declare a @code{TARGET_@var{x}}
macro that has the value 1 when bit @code{MASK_@var{x}} is set and
0 otherwise.

They are primarily intended to declare target masks that are not
associated with user options, either because these masks represent
internal switches or because the options are not available on all
configurations and yet the masks always need to be defined.
@end itemize

@node Option properties
@section Option properties

The second field of an option record can specify any of the following
properties.  When an option takes an argument, it is enclosed in parentheses
following the option property name.  The parser that handles option files
is quite simplistic, and will be tricked by any nested parentheses within
the argument text itself; in this case, the entire option argument can
be wrapped in curly braces within the parentheses to demarcate it, e.g.:

@smallexample
Condition(@{defined (USE_CYGWIN_LIBSTDCXX_WRAPPERS)@})
@end smallexample

@table @code
@item Common
The option is available for all languages and targets.

@item Target
The option is available for all languages but is target-specific.

@item Driver
The option is handled by the compiler driver using code not shared
with the compilers proper (@file{cc1} etc.).

@item @var{language}
The option is available when compiling for the given language.

It is possible to specify several different languages for the same
option.  Each @var{language} must have been declared by an earlier
@code{Language} record.  @xref{Option file format}.

@item RejectDriver
The option is only handled by the compilers proper (@file{cc1} etc.)@:
and should not be accepted by the driver.

@item RejectNegative
The option does not have a ``no-'' form.  All options beginning with
``f'', ``W'' or ``m'' are assumed to have a ``no-'' form unless this
property is used.

@item Negative(@var{othername})
The option will turn off another option @var{othername}, which is
the option name with the leading ``-'' removed.  This chain action will
propagate through the @code{Negative} property of the option to be
turned off.  The driver will prune options, removing those that are
turned off by some later option.  This pruning is not done for options
with @code{Joined} or @code{JoinedOrMissing} properties, unless the
options have both the @code{RejectNegative} property and the @code{Negative}
property mentions itself.

As a consequence, if you have a group of mutually-exclusive
options, their @code{Negative} properties should form a circular chain.
For example, if options @option{-@var{a}}, @option{-@var{b}} and
@option{-@var{c}} are mutually exclusive, their respective @code{Negative}
properties should be @samp{Negative(@var{b})}, @samp{Negative(@var{c})}
and @samp{Negative(@var{a})}.

@item Joined
@itemx Separate
The option takes a mandatory argument.  @code{Joined} indicates
that the option and argument can be included in the same @code{argv}
entry (as with @code{-mflush-func=@var{name}}, for example).
@code{Separate} indicates that the option and argument can be
separate @code{argv} entries (as with @code{-o}).  An option is
allowed to have both of these properties.

@item JoinedOrMissing
The option takes an optional argument.  If the argument is given,
it will be part of the same @code{argv} entry as the option itself.

This property cannot be used alongside @code{Joined} or @code{Separate}.

@item MissingArgError(@var{message})
For an option marked @code{Joined} or @code{Separate}, the message
@var{message} will be used as an error message if the mandatory
argument is missing; for options without @code{MissingArgError}, a
generic error message is used.  @var{message} should contain a single
@samp{%qs} format, which will be used to format the name of the option
passed.

@item Args(@var{n})
For an option marked @code{Separate}, indicate that it takes @var{n}
arguments.  The default is 1.

@item UInteger
The option's argument is a non-negative integer consisting of either
decimal or hexadecimal digits interpreted as @code{int}.  Hexadecimal
integers may optionally start with the @code{0x} or @code{0X} prefix.
The option parser validates and converts the argument before passing
it to the relevant option handler.  @code{UInteger} should also be used
with options like @code{-falign-loops} where both @code{-falign-loops}
and @code{-falign-loops}=@var{n} are supported to make sure the saved
options are given a full integer.  Positive values of the argument in
excess of @code{INT_MAX} wrap around zero.

@item Host_Wide_Int
The option's argument is a non-negative integer consisting of either
decimal or hexadecimal digits interpreted as the widest integer type
on the host.  As with an @code{UInteger} argument, hexadecimal integers
may optionally start with the @code{0x} or @code{0X} prefix.  The option
parser validates and converts the argument before passing it to
the relevant option handler.  @code{Host_Wide_Int} should be used with
options that need to accept very large values.  Positive values of
the argument in excess of @code{HOST_WIDE_INT_M1U} are assigned
@code{HOST_WIDE_INT_M1U}.

@item IntegerRange(@var{n}, @var{m})
The options's arguments are integers of type @code{int}.  The option's
parser validates that the value of an option integer argument is within
the closed range [@var{n}, @var{m}].

@item ByteSize
A property applicable only to @code{UInteger} or @code{Host_Wide_Int}
arguments.  The option's integer argument is interpreted as if in infinite
precision using saturation arithmetic in the corresponding type.  The argument
may be followed by a @samp{byte-size} suffix designating a multiple of bytes
such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively,
@code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and @code{GiB}
for gigabyte and gigibyte, and so on.  @code{ByteSize} should be used for
with options that take a very large argument representing a size in bytes,
such as @option{-Wlarger-than=}.

@item ToLower
The option's argument should be converted to lowercase as part of
putting it in canonical form, and before comparing with the strings
indicated by any @code{Enum} property.

@item NoDriverArg
For an option marked @code{Separate}, the option only takes an
argument in the compiler proper, not in the driver.  This is for
compatibility with existing options that are used both directly and
via @option{-Wp,}; new options should not have this property.

@item Var(@var{var})
The state of this option should be stored in variable @var{var}
(actually a macro for @code{global_options.x_@var{var}}).
The way that the state is stored depends on the type of option:

@item WarnRemoved
The option is removed and every usage of such option will
result in a warning.  We use it option backward compatibility.

@item Var(@var{var}, @var{set})
The option controls an integer variable @var{var} and is active when
@var{var} equals @var{set}.  The option parser will set @var{var} to
@var{set} when the positive form of the option is used and @code{!@var{set}}
when the ``no-'' form is used.

@var{var} is declared in the same way as for the single-argument form
described above.

@itemize @bullet
@item
If the option uses the @code{Mask} or @code{InverseMask} properties,
@var{var} is the integer variable that contains the mask.

@item
If the option is a normal on/off switch, @var{var} is an integer
variable that is nonzero when the option is enabled.  The options
parser will set the variable to 1 when the positive form of the
option is used and 0 when the ``no-'' form is used.

@item
If the option takes an argument and has the @code{UInteger} property,
@var{var} is an integer variable that stores the value of the argument.

@item
If the option takes an argument and has the @code{Enum} property,
@var{var} is a variable (type given in the @code{Type} property of the
@samp{Enum} record whose @code{Name} property has the same argument as
the @code{Enum} property of this option) that stores the value of the
argument.

@item
If the option has the @code{Defer} property, @var{var} is a pointer to
a @code{VEC(cl_deferred_option,heap)} that stores the option for later
processing.  (@var{var} is declared with type @code{void *} and needs
to be cast to @code{VEC(cl_deferred_option,heap)} before use.)

@item
Otherwise, if the option takes an argument, @var{var} is a pointer to
the argument string.  The pointer will be null if the argument is optional
and wasn't given.
@end itemize

The option-processing script will usually zero-initialize @var{var}.
You can modify this behavior using @code{Init}.

@item Init(@var{value})
The variable specified by the @code{Var} property should be statically
initialized to @var{value}.  If more than one option using the same
variable specifies @code{Init}, all must specify the same initializer.

@item Mask(@var{name})
The option is associated with a bit in the @code{target_flags}
variable (@pxref{Run-time Target}) and is active when that bit is set.
You may also specify @code{Var} to select a variable other than
@code{target_flags}.

The options-processing script will automatically allocate a unique bit
for the option.  If the option is attached to @samp{target_flags},
the script will set the macro @code{MASK_@var{name}} to the appropriate
bitmask.  It will also declare a @code{TARGET_@var{name}} macro that has
the value 1 when the option is active and 0 otherwise.  If you use @code{Var}
to attach the option to a different variable, the bitmask macro with be
called @code{OPTION_MASK_@var{name}}.

@item InverseMask(@var{othername})
@itemx InverseMask(@var{othername}, @var{thisname})
The option is the inverse of another option that has the
@code{Mask(@var{othername})} property.  If @var{thisname} is given,
the options-processing script will declare a @code{TARGET_@var{thisname}}
macro that is 1 when the option is active and 0 otherwise.

@item Enum(@var{name})
The option's argument is a string from the set of strings associated
with the corresponding @samp{Enum} record.  The string is checked and
converted to the integer specified in the corresponding
@samp{EnumValue} record before being passed to option handlers.

@item Defer
The option should be stored in a vector, specified with @code{Var},
for later processing.

@item Alias(@var{opt})
@itemx Alias(@var{opt}, @var{arg})
@itemx Alias(@var{opt}, @var{posarg}, @var{negarg})
The option is an alias for @option{-@var{opt}} (or the negative form
of that option, depending on @code{NegativeAlias}).  In the first form,
any argument passed to the alias is considered to be passed to
@option{-@var{opt}}, and @option{-@var{opt}} is considered to be
negated if the alias is used in negated form.  In the second form, the
alias may not be negated or have an argument, and @var{posarg} is
considered to be passed as an argument to @option{-@var{opt}}.  In the
third form, the alias may not have an argument, if the alias is used
in the positive form then @var{posarg} is considered to be passed to
@option{-@var{opt}}, and if the alias is used in the negative form
then @var{negarg} is considered to be passed to @option{-@var{opt}}.

Aliases should not specify @code{Var} or @code{Mask} or
@code{UInteger}.  Aliases should normally specify the same languages
as the target of the alias; the flags on the target will be used to
determine any diagnostic for use of an option for the wrong language,
while those on the alias will be used to identify what command-line
text is the option and what text is any argument to that option.

When an @code{Alias} definition is used for an option, driver specs do
not need to handle it and no @samp{OPT_} enumeration value is defined
for it; only the canonical form of the option will be seen in those
places.

@item NegativeAlias
For an option marked with @code{Alias(@var{opt})}, the option is
considered to be an alias for the positive form of @option{-@var{opt}}
if negated and for the negative form of @option{-@var{opt}} if not
negated.  @code{NegativeAlias} may not be used with the forms of
@code{Alias} taking more than one argument.

@item Ignore
This option is ignored apart from printing any warning specified using
@code{Warn}.  The option will not be seen by specs and no @samp{OPT_}
enumeration value is defined for it.

@item SeparateAlias
For an option marked with @code{Joined}, @code{Separate} and
@code{Alias}, the option only acts as an alias when passed a separate
argument; with a joined argument it acts as a normal option, with an
@samp{OPT_} enumeration value.  This is for compatibility with the
Java @option{-d} option and should not be used for new options.

@item Warn(@var{message})
If this option is used, output the warning @var{message}.
@var{message} is a format string, either taking a single operand with
a @samp{%qs} format which is the option name, or not taking any
operands, which is passed to the @samp{warning} function.  If an alias
is marked @code{Warn}, the target of the alias must not also be marked
@code{Warn}.

@item Warning
This is a warning option and should be shown as such in
@option{--help} output.  This flag does not currently affect anything
other than @option{--help}.

@item Optimization
This is an optimization option.  It should be shown as such in
@option{--help} output, and any associated variable named using
@code{Var} should be saved and restored when the optimization level is
changed with @code{optimize} attributes.

@item PerFunction
This is an option that can be overridden on a per-function basis.
@code{Optimization} implies @code{PerFunction}, but options that do not
affect executable code generation may use this flag instead, so that the
option is not taken into account in ways that might affect executable
code generation.

@item Param
This is an option that is a parameter.

@item Undocumented
The option is deliberately missing documentation and should not
be included in the @option{--help} output.

@item Condition(@var{cond})
The option should only be accepted if preprocessor condition
@var{cond} is true.  Note that any C declarations associated with the
option will be present even if @var{cond} is false; @var{cond} simply
controls whether the option is accepted and whether it is printed in
the @option{--help} output.

@item Save
Build the @code{cl_target_option} structure to hold a copy of the
option, add the functions @code{cl_target_option_save} and
@code{cl_target_option_restore} to save and restore the options.

@item SetByCombined
The option may also be set by a combined option such as
@option{-ffast-math}.  This causes the @code{gcc_options} struct to
have a field @code{frontend_set_@var{name}}, where @code{@var{name}}
is the name of the field holding the value of this option (without the
leading @code{x_}).  This gives the front end a way to indicate that
the value has been set explicitly and should not be changed by the
combined option.  For example, some front ends use this to prevent
@option{-ffast-math} and @option{-fno-fast-math} from changing the
value of @option{-fmath-errno} for languages that do not use
@code{errno}.

@item EnabledBy(@var{opt})
@itemx EnabledBy(@var{opt} || @var{opt2})
@itemx EnabledBy(@var{opt} && @var{opt2})
If not explicitly set, the option is set to the value of
@option{-@var{opt}}; multiple options can be given, separated by
@code{||}.  The third form using @code{&&} specifies that the option is
only set if both @var{opt} and @var{opt2} are set. The options @var{opt}
and @var{opt2} must have the @code{Common} property; otherwise, use
@code{LangEnabledBy}.

@item LangEnabledBy(@var{language}, @var{opt})
@itemx LangEnabledBy(@var{language}, @var{opt}, @var{posarg}, @var{negarg})
When compiling for the given language, the option is set to the value
of @option{-@var{opt}}, if not explicitly set. @var{opt} can be also a list
of @code{||} separated options. In the second form, if
@var{opt} is used in the positive form then @var{posarg} is considered
to be passed to the option, and if @var{opt} is used in the negative
form then @var{negarg} is considered to be passed to the option.  It
is possible to specify several different languages.  Each
@var{language} must have been declared by an earlier @code{Language}
record.  @xref{Option file format}.

@item NoDWARFRecord
The option is omitted from the producer string written by
@option{-grecord-gcc-switches}.

@item PchIgnore
Even if this is a target option, this option will not be recorded / compared
to determine if a precompiled header file matches.

@item CPP(@var{var})
The state of this option should be kept in sync with the preprocessor
option @var{var}.  If this property is set, then properties @code{Var}
and @code{Init} must be set as well.

@item CppReason(@var{CPP_W_Enum})
This warning option corresponds to @code{cpplib.h} warning reason code
@var{CPP_W_Enum}.  This should only be used for warning options of the
C-family front-ends.

@end table