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8.1 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:

• A language definition record. These records have two fields: the string ‘Language’ and the name of the language. Once a language has been declared in this way, it can be used as an option property. See Option properties.
• A target specific save record to save additional information. These records have two fields: the string ‘TargetSave’, and a declaration type to go in the cl_target_option structure.
• A variable record to define a variable used to store option information. These records have two fields: the string ‘Variable’, and a declaration of the type and name of the variable, optionally with an initializer (but without any trailing ‘;’). 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 Var properties.
• A variable record to define a variable used to store option information. These records have two fields: the string ‘TargetVariable’, and a declaration of the type and name of the variable, optionally with an initializer (but without any trailing ‘;’). ‘TargetVariable’ is a combination of ‘Variable’ and ‘TargetSave’ records in that the variable is defined in the gcc_options structure, but these variables are also stored in the cl_target_option structure. The variables are saved in the target save code and restored in the target restore code.
• A variable record to record any additional files that the 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 ‘HeaderInclude’ and the name of the include file.
• A variable record to record any additional files that the options.cc or options-save.cc file should include. This is useful to provide inline functions needed for target variables and/or #ifdef sequences to properly set up the initialization. These records have two fields: the string ‘SourceInclude’ and the name of the include file.
• 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 ‘Enum’, a space-separated list of properties and help text used to describe the set of strings in --help output. Properties use the same format as option properties; the following are valid:

  Name(name)

  This property is required; name must be a name (suitable for use in C identifiers) used to identify the set of strings in Enum option properties.

  Type(type)

  This property is required; type is the C type for variables set by options using this enumeration together with Var.

  UnknownError(message)

  The message message will be used as an error message if the argument is invalid; for enumerations without UnknownError, a generic error message is used. message should contain a single ‘%qs’ format, which will be used to format the invalid argument.

• An enumeration value record to define one of the strings in a set given in an ‘Enum’ record. These records have two fields: the string ‘EnumValue’ and a space-separated list of properties. Properties use the same format as option properties; the following are valid:

  Enum(name)

  This property is required; name says which ‘Enum’ record this ‘EnumValue’ record corresponds to.

  String(string)

  This property is required; string is the string option argument being described by this record.

  Value(value)

  This property is required; it says what value (representable as int) should be used for the given string.

  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.

  DriverOnly

  This property is optional. If present, the present string will only be accepted by the driver. This is used for cases such as -march=native that are processed by the driver so that ‘gcc -v’ shows how the options chosen depended on the system on which the compiler was run.

  Set(number)

  This property is optional, required for enumerations used in EnumSet options. number should be decimal number between 1 and 64 inclusive and divides the enumeration into a set of sets of mutually exclusive arguments. Arguments with the same number can’t be specified together in the same option, but arguments with different number can. value needs to be chosen such that a mask of all value values from the same set number bitwise ored doesn’t overlap with masks for other sets. When -foption=arg_from_set1,arg_from_set4 and -fno-option=arg_from_set3 are used, the effect is that previous value of the Var will get bits from set 1 and 4 masks cleared, ored Value of arg_from_set1 and arg_from_set4 and then will get bits from set 3 mask cleared.

• An option definition record. These records have the following fields:
  1. the name of the option, with the leading “-” removed
  2. a space-separated list of option properties (see Option properties)
  3. the help text to use for --help (omitted if the second field contains the Undocumented property).

  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 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.

  There is no support for different help texts for different languages. If an option is supported for multiple languages, use a generic description that is correct for all of them.

  If an option has multiple option definition records (in different front ends’ *.opt files, and/or gcc/common.opt, for example), convention is to not duplicate the help text for each of them, but instead put a comment like ; documented in common.opt in place of the help text for all but one of the multiple option definition records.

• A target mask record. These records have one field of the form ‘Mask(x)’. The options-processing script will automatically allocate a bit in target_flags (see Run-time Target Specification) for each mask name x and set the macro MASK_x to the appropriate bitmask. It will also declare a TARGET_x macro that has the value 1 when bit MASK_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.