Re: target_flags

[DJ Delorie <dj at redhat dot com>]

> Could you please just say explicitly in the documentation that the
> reason it's called a default value is because you can do something
> like this with two entries in the table?  And then go ahead and
> check it in.

I think it would be better to explain more clearly how it works,
then note that it can be used as a default value.  How about this?


Each subgrouping contains a string constant, that defines the option
name, the address of a variable, a description string, and a value.
Non-empty description strings should be marked with @code{N_(@dots{})}
for @command{xgettext}.  Please do not mark empty strings because the
empty string is reserved by GNU gettext. @code{gettext("")} returns the
header entry of the message catalog with meta information, not the empty
string.

If the value listed in the table is @code{NULL}, then the variable, type
@code{char *}, is set to the variable part of the given option if the
fixed part matches.  In other words, if the first part of the option
matches what's in the table, the variable will be set to point to the
rest of the option.  This allows the user to specify a value for that
option.  The actual option name is made by appending @samp{-m} to the
specified name.  Again, each option should also be documented in
@file{invoke.texi}.

If the value listed in the table is non- at code{NULL}, then the option
must match the option in the table exactly (with @samp{-m}), and the
variable is set to point to the value listed in the table.

Here is an example which defines @option{-mshort-data- at var{number}} dot   If the
given option is @option{-mshort-data-512}, the variable @code{m88k_short_data}
will be set to the string @code{"512"}.

@smallexample
extern char *m88k_short_data;
#define TARGET_OPTIONS \
 @{ @{ "short-data-", &m88k_short_data, \
     N_("Specify the size of the short data section"), 0 @} @}
@end smallexample

Here is an variant of the above that allows the user to also specify
just @option{-mshort-data} where a default of @code{"64"} is used.

@smallexample
extern char *m88k_short_data;
#define TARGET_OPTIONS \
 @{ @{ "short-data-", &m88k_short_data, \
     N_("Specify the size of the short data section"), 0 @} \
    @{ "short-data", &m88k_short_data, "", "64" @},
    @}
@end smallexample

Here is an example which defines @option{-mno-alu}, @option{-malu1}, and
@option{-malu2} as a three-state switch, along with suitable macros for
checking the state of the option (documentation is elided for brevity).

@smallexample
[chip.c]
char *chip_alu = ""; /* Specify default here.  */

[chip.h]
extern char *chip_alu;
#define TARGET_OPTIONS \
  @{ @{ "no-alu", &chip_alu, "", "" @}, \
     @{ "alu1", &chip_alu, "", "1" @}, \
     @{ "alu2", &chip_alu, "", "2" @}, @}
#define TARGET_ALU (chip_alu[0] != '\0')
#define TARGET_ALU1 (chip_alu[0] == '1')
#define TARGET_ALU2 (chip_alu[0] == '2')
@end smallexample