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+This is Info file gcc.info, produced by Makeinfo-1.63 from the input
+file gcc.texi.
+
+   This file documents the use and the internals of the GNU compiler.
+
+   Published by the Free Software Foundation 59 Temple Place - Suite 330
+Boston, MA 02111-1307 USA
+
+   Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 Free Software
+Foundation, Inc.
+
+   Permission is granted to make and distribute verbatim copies of this
+manual provided the copyright notice and this permission notice are
+preserved on all copies.
+
+   Permission is granted to copy and distribute modified versions of
+this manual under the conditions for verbatim copying, provided also
+that the sections entitled "GNU General Public License," "Funding for
+Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are
+included exactly as in the original, and provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+   Permission is granted to copy and distribute translations of this
+manual into another language, under the above conditions for modified
+versions, except that the sections entitled "GNU General Public
+License," "Funding for Free Software," and "Protect Your Freedom--Fight
+`Look And Feel'", and this permission notice, may be included in
+translations approved by the Free Software Foundation instead of in the
+original English.
+
+
+File: gcc.info,  Node: Constructors,  Next: Labeled Elements,  Prev: Initializers,  Up: C Extensions
+
+Constructor Expressions
+=======================
+
+   GNU C supports constructor expressions.  A constructor looks like a
+cast containing an initializer.  Its value is an object of the type
+specified in the cast, containing the elements specified in the
+initializer.
+
+   Usually, the specified type is a structure.  Assume that `struct
+foo' and `structure' are declared as shown:
+
+     struct foo {int a; char b[2];} structure;
+
+Here is an example of constructing a `struct foo' with a constructor:
+
+     structure = ((struct foo) {x + y, 'a', 0});
+
+This is equivalent to writing the following:
+
+     {
+       struct foo temp = {x + y, 'a', 0};
+       structure = temp;
+     }
+
+   You can also construct an array.  If all the elements of the
+constructor are (made up of) simple constant expressions, suitable for
+use in initializers, then the constructor is an lvalue and can be
+coerced to a pointer to its first element, as shown here:
+
+     char **foo = (char *[]) { "x", "y", "z" };
+
+   Array constructors whose elements are not simple constants are not
+very useful, because the constructor is not an lvalue.  There are only
+two valid ways to use it: to subscript it, or initialize an array
+variable with it.  The former is probably slower than a `switch'
+statement, while the latter does the same thing an ordinary C
+initializer would do.  Here is an example of subscripting an array
+constructor:
+
+     output = ((int[]) { 2, x, 28 }) [input];
+
+   Constructor expressions for scalar types and union types are is also
+allowed, but then the constructor expression is equivalent to a cast.
+
+
+File: gcc.info,  Node: Labeled Elements,  Next: Cast to Union,  Prev: Constructors,  Up: C Extensions
+
+Labeled Elements in Initializers
+================================
+
+   Standard C requires the elements of an initializer to appear in a
+fixed order, the same as the order of the elements in the array or
+structure being initialized.
+
+   In GNU C you can give the elements in any order, specifying the array
+indices or structure field names they apply to.  This extension is not
+implemented in GNU C++.
+
+   To specify an array index, write `[INDEX]' or `[INDEX] =' before the
+element value.  For example,
+
+     int a[6] = { [4] 29, [2] = 15 };
+
+is equivalent to
+
+     int a[6] = { 0, 0, 15, 0, 29, 0 };
+
+The index values must be constant expressions, even if the array being
+initialized is automatic.
+
+   To initialize a range of elements to the same value, write `[FIRST
+... LAST] = VALUE'.  For example,
+
+     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
+
+Note that the length of the array is the highest value specified plus
+one.
+
+   In a structure initializer, specify the name of a field to initialize
+with `FIELDNAME:' before the element value.  For example, given the
+following structure,
+
+     struct point { int x, y; };
+
+the following initialization
+
+     struct point p = { y: yvalue, x: xvalue };
+
+is equivalent to
+
+     struct point p = { xvalue, yvalue };
+
+   Another syntax which has the same meaning is `.FIELDNAME ='., as
+shown here:
+
+     struct point p = { .y = yvalue, .x = xvalue };
+
+   You can also use an element label (with either the colon syntax or
+the period-equal syntax) when initializing a union, to specify which
+element of the union should be used.  For example,
+
+     union foo { int i; double d; };
+     
+     union foo f = { d: 4 };
+
+will convert 4 to a `double' to store it in the union using the second
+element.  By contrast, casting 4 to type `union foo' would store it
+into the union as the integer `i', since it is an integer.  (*Note Cast
+to Union::.)
+
+   You can combine this technique of naming elements with ordinary C
+initialization of successive elements.  Each initializer element that
+does not have a label applies to the next consecutive element of the
+array or structure.  For example,
+
+     int a[6] = { [1] = v1, v2, [4] = v4 };
+
+is equivalent to
+
+     int a[6] = { 0, v1, v2, 0, v4, 0 };
+
+   Labeling the elements of an array initializer is especially useful
+when the indices are characters or belong to an `enum' type.  For
+example:
+
+     int whitespace[256]
+       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
+           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
+
+
+File: gcc.info,  Node: Case Ranges,  Next: Function Attributes,  Prev: Cast to Union,  Up: C Extensions
+
+Case Ranges
+===========
+
+   You can specify a range of consecutive values in a single `case'
+label, like this:
+
+     case LOW ... HIGH:
+
+This has the same effect as the proper number of individual `case'
+labels, one for each integer value from LOW to HIGH, inclusive.
+
+   This feature is especially useful for ranges of ASCII character
+codes:
+
+     case 'A' ... 'Z':
+
+   *Be careful:* Write spaces around the `...', for otherwise it may be
+parsed wrong when you use it with integer values.  For example, write
+this:
+
+     case 1 ... 5:
+
+rather than this:
+
+     case 1...5:
+
+
+File: gcc.info,  Node: Cast to Union,  Next: Case Ranges,  Prev: Labeled Elements,  Up: C Extensions
+
+Cast to a Union Type
+====================
+
+   A cast to union type is similar to other casts, except that the type
+specified is a union type.  You can specify the type either with `union
+TAG' or with a typedef name.  A cast to union is actually a constructor
+though, not a cast, and hence does not yield an lvalue like normal
+casts.  (*Note Constructors::.)
+
+   The types that may be cast to the union type are those of the members
+of the union.  Thus, given the following union and variables:
+
+     union foo { int i; double d; };
+     int x;
+     double y;
+
+both `x' and `y' can be cast to type `union' foo.
+
+   Using the cast as the right-hand side of an assignment to a variable
+of union type is equivalent to storing in a member of the union:
+
+     union foo u;
+     ...
+     u = (union foo) x  ==  u.i = x
+     u = (union foo) y  ==  u.d = y
+
+   You can also use the union cast as a function argument:
+
+     void hack (union foo);
+     ...
+     hack ((union foo) x);
+
+
+File: gcc.info,  Node: Function Attributes,  Next: Function Prototypes,  Prev: Case Ranges,  Up: C Extensions
+
+Declaring Attributes of Functions
+=================================
+
+   In GNU C, you declare certain things about functions called in your
+program which help the compiler optimize function calls and check your
+code more carefully.
+
+   The keyword `__attribute__' allows you to specify special attributes
+when making a declaration.  This keyword is followed by an attribute
+specification inside double parentheses.  Eight attributes, `noreturn',
+`const', `format', `section', `constructor', `destructor', `unused' and
+`weak' are currently defined for functions.  Other attributes, including
+`section' are supported for variables declarations (*note Variable
+Attributes::.) and for types (*note Type Attributes::.).
+
+   You may also specify attributes with `__' preceding and following
+each keyword.  This allows you to use them in header files without
+being concerned about a possible macro of the same name.  For example,
+you may use `__noreturn__' instead of `noreturn'.
+
+`noreturn'
+     A few standard library functions, such as `abort' and `exit',
+     cannot return.  GNU CC knows this automatically.  Some programs
+     define their own functions that never return.  You can declare them
+     `noreturn' to tell the compiler this fact.  For example,
+
+          void fatal () __attribute__ ((noreturn));
+          
+          void
+          fatal (...)
+          {
+            ... /* Print error message. */ ...
+            exit (1);
+          }
+
+     The `noreturn' keyword tells the compiler to assume that `fatal'
+     cannot return.  It can then optimize without regard to what would
+     happen if `fatal' ever did return.  This makes slightly better
+     code.  More importantly, it helps avoid spurious warnings of
+     uninitialized variables.
+
+     Do not assume that registers saved by the calling function are
+     restored before calling the `noreturn' function.
+
+     It does not make sense for a `noreturn' function to have a return
+     type other than `void'.
+
+     The attribute `noreturn' is not implemented in GNU C versions
+     earlier than 2.5.  An alternative way to declare that a function
+     does not return, which works in the current version and in some
+     older versions, is as follows:
+
+          typedef void voidfn ();
+          
+          volatile voidfn fatal;
+
+`const'
+     Many functions do not examine any values except their arguments,
+     and have no effects except the return value.  Such a function can
+     be subject to common subexpression elimination and loop
+     optimization just as an arithmetic operator would be.  These
+     functions should be declared with the attribute `const'.  For
+     example,
+
+          int square (int) __attribute__ ((const));
+
+     says that the hypothetical function `square' is safe to call fewer
+     times than the program says.
+
+     The attribute `const' is not implemented in GNU C versions earlier
+     than 2.5.  An alternative way to declare that a function has no
+     side effects, which works in the current version and in some older
+     versions, is as follows:
+
+          typedef int intfn ();
+          
+          extern const intfn square;
+
+     This approach does not work in GNU C++ from 2.6.0 on, since the
+     language specifies that the `const' must be attached to the return
+     value.
+
+     Note that a function that has pointer arguments and examines the
+     data pointed to must *not* be declared `const'.  Likewise, a
+     function that calls a non-`const' function usually must not be
+     `const'.  It does not make sense for a `const' function to return
+     `void'.
+
+`format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
+     The `format' attribute specifies that a function takes `printf' or
+     `scanf' style arguments which should be type-checked against a
+     format string.  For example, the declaration:
+
+          extern int
+          my_printf (void *my_object, const char *my_format, ...)
+                __attribute__ ((format (printf, 2, 3)));
+
+     causes the compiler to check the arguments in calls to `my_printf'
+     for consistency with the `printf' style format string argument
+     `my_format'.
+
+     The parameter ARCHETYPE determines how the format string is
+     interpreted, and should be either `printf' or `scanf'.  The
+     parameter STRING-INDEX specifies which argument is the format
+     string argument (starting from 1), while FIRST-TO-CHECK is the
+     number of the first argument to check against the format string.
+     For functions where the arguments are not available to be checked
+     (such as `vprintf'), specify the third parameter as zero.  In this
+     case the compiler only checks the format string for consistency.
+
+     In the example above, the format string (`my_format') is the second
+     argument of the function `my_print', and the arguments to check
+     start with the third argument, so the correct parameters for the
+     format attribute are 2 and 3.
+
+     The `format' attribute allows you to identify your own functions
+     which take format strings as arguments, so that GNU CC can check
+     the calls to these functions for errors.  The compiler always
+     checks formats for the ANSI library functions `printf', `fprintf',
+     `sprintf', `scanf', `fscanf', `sscanf', `vprintf', `vfprintf' and
+     `vsprintf' whenever such warnings are requested (using
+     `-Wformat'), so there is no need to modify the header file
+     `stdio.h'.
+
+`section ("section-name")'
+     Normally, the compiler places the code it generates in the `text'
+     section.  Sometimes, however, you need additional sections, or you
+     need certain particular functions to appear in special sections.
+     The `section' attribute specifies that a function lives in a
+     particular section.  For example, the declaration:
+
+          extern void foobar (void) __attribute__ ((section ("bar")));
+
+     puts the function `foobar' in the `bar' section.
+
+     Some file formats do not support arbitrary sections so the
+     `section' attribute is not available on all platforms.  If you
+     need to map the entire contents of a module to a particular
+     section, consider using the facilities of the linker instead.
+
+`constructor'
+`destructor'
+     The `constructor' attribute causes the function to be called
+     automatically before execution enters `main ()'.  Similarly, the
+     `destructor' attribute causes the function to be called
+     automatically after `main ()' has completed or `exit ()' has been
+     called.  Functions with these attributes are useful for
+     initializing data that will be used implicitly during the
+     execution of the program.
+
+     These attributes are not currently implemented for Objective C.
+
+`unused'
+     This attribute, attached to a function, means that the function is
+     meant to be possibly unused.  GNU CC will not produce a warning
+     for this function.
+
+`weak'
+     The `weak' attribute causes the declaration to be emitted as a weak
+     symbol rather than a global.  This is primarily useful in defining
+     library functions which can be overridden in user code, though it
+     can also be used with non-function declarations.  Weak symbols are
+     supported for ELF targets, and also for a.out targets when using
+     the GNU assembler and linker.
+
+`alias ("target")'
+     The `alias' attribute causes the declaration to be emitted as an
+     alias for another symbol, which must be specified.  For instance,
+
+          void __f () { /* do something */; }
+          void f () __attribute__ ((weak, alias ("__f")));
+
+     declares `f' to be a weak alias for `__f'.  In C++, the mangled
+     name for the target must be used.
+
+`regparm (NUMBER)'
+     On the Intel 386, the `regparm' attribute causes the compiler to
+     pass up to NUMBER integer arguments in registers EAX, EDX, and ECX
+     instead of on the stack.  Functions that take a variable number of
+     arguments will continue to be passed all of their arguments on the
+     stack.
+
+`stdcall'
+     On the Intel 386, the `stdcall' attribute causes the compiler to
+     assume that the called function will pop off the stack space used
+     to pass arguments, unless it takes a variable number of arguments.
+
+`cdecl'
+     On the Intel 386, the `cdecl' attribute causes the compiler to
+     assume that the called function will pop off the stack space used
+     to pass arguments, unless it takes a variable number of arguments.
+     This is useful to override the effects of the `-mrtd' switch.
+
+   You can specify multiple attributes in a declaration by separating
+them by commas within the double parentheses or by immediately
+following an attribute declaration with another attribute declaration.
+
+   Some people object to the `__attribute__' feature, suggesting that
+ANSI C's `#pragma' should be used instead.  There are two reasons for
+not doing this.
+
+  1. It is impossible to generate `#pragma' commands from a macro.
+
+  2. There is no telling what the same `#pragma' might mean in another
+     compiler.
+
+   These two reasons apply to almost any application that might be
+proposed for `#pragma'.  It is basically a mistake to use `#pragma' for
+*anything*.
+
+
+File: gcc.info,  Node: Function Prototypes,  Next: C++ Comments,  Prev: Function Attributes,  Up: C Extensions
+
+Prototypes and Old-Style Function Definitions
+=============================================
+
+   GNU C extends ANSI C to allow a function prototype to override a
+later old-style non-prototype definition.  Consider the following
+example:
+
+     /* Use prototypes unless the compiler is old-fashioned.  */
+     #if __STDC__
+     #define P(x) x
+     #else
+     #define P(x) ()
+     #endif
+     
+     /* Prototype function declaration.  */
+     int isroot P((uid_t));
+     
+     /* Old-style function definition.  */
+     int
+     isroot (x)   /* ??? lossage here ??? */
+          uid_t x;
+     {
+       return x == 0;
+     }
+
+   Suppose the type `uid_t' happens to be `short'.  ANSI C does not
+allow this example, because subword arguments in old-style
+non-prototype definitions are promoted.  Therefore in this example the
+function definition's argument is really an `int', which does not match
+the prototype argument type of `short'.
+
+   This restriction of ANSI C makes it hard to write code that is
+portable to traditional C compilers, because the programmer does not
+know whether the `uid_t' type is `short', `int', or `long'.  Therefore,
+in cases like these GNU C allows a prototype to override a later
+old-style definition.  More precisely, in GNU C, a function prototype
+argument type overrides the argument type specified by a later
+old-style definition if the former type is the same as the latter type
+before promotion.  Thus in GNU C the above example is equivalent to the
+following:
+
+     int isroot (uid_t);
+     
+     int
+     isroot (uid_t x)
+     {
+       return x == 0;
+     }
+
+   GNU C++ does not support old-style function definitions, so this
+extension is irrelevant.
+
+
+File: gcc.info,  Node: C++ Comments,  Next: Dollar Signs,  Prev: Function Prototypes,  Up: C Extensions
+
+C++ Style Comments
+==================
+
+   In GNU C, you may use C++ style comments, which start with `//' and
+continue until the end of the line.  Many other C implementations allow
+such comments, and they are likely to be in a future C standard.
+However, C++ style comments are not recognized if you specify `-ansi'
+or `-traditional', since they are incompatible with traditional
+constructs like `dividend//*comment*/divisor'.
+
+
+File: gcc.info,  Node: Dollar Signs,  Next: Character Escapes,  Prev: C++ Comments,  Up: C Extensions
+
+Dollar Signs in Identifier Names
+================================
+
+   In GNU C, you may use dollar signs in identifier names.  This is
+because many traditional C implementations allow such identifiers.
+
+   On some machines, dollar signs are allowed in identifiers if you
+specify `-traditional'.  On a few systems they are allowed by default,
+even if you do not use `-traditional'.  But they are never allowed if
+you specify `-ansi'.
+
+   There are certain ANSI C programs (obscure, to be sure) that would
+compile incorrectly if dollar signs were permitted in identifiers.  For
+example:
+
+     #define foo(a) #a
+     #define lose(b) foo (b)
+     #define test$
+     lose (test)
+
+
+File: gcc.info,  Node: Character Escapes,  Next: Variable Attributes,  Prev: Dollar Signs,  Up: C Extensions
+
+The Character ESC in Constants
+==============================
+
+   You can use the sequence `\e' in a string or character constant to
+stand for the ASCII character ESC.
+
+
+File: gcc.info,  Node: Alignment,  Next: Inline,  Prev: Type Attributes,  Up: C Extensions
+
+Inquiring on Alignment of Types or Variables
+============================================
+
+   The keyword `__alignof__' allows you to inquire about how an object
+is aligned, or the minimum alignment usually required by a type.  Its
+syntax is just like `sizeof'.
+
+   For example, if the target machine requires a `double' value to be
+aligned on an 8-byte boundary, then `__alignof__ (double)' is 8.  This
+is true on many RISC machines.  On more traditional machine designs,
+`__alignof__ (double)' is 4 or even 2.
+
+   Some machines never actually require alignment; they allow reference
+to any data type even at an odd addresses.  For these machines,
+`__alignof__' reports the *recommended* alignment of a type.
+
+   When the operand of `__alignof__' is an lvalue rather than a type,
+the value is the largest alignment that the lvalue is known to have.
+It may have this alignment as a result of its data type, or because it
+is part of a structure and inherits alignment from that structure.  For
+example, after this declaration:
+
+     struct foo { int x; char y; } foo1;
+
+the value of `__alignof__ (foo1.y)' is probably 2 or 4, the same as
+`__alignof__ (int)', even though the data type of `foo1.y' does not
+itself demand any alignment.
+
+   A related feature which lets you specify the alignment of an object
+is `__attribute__ ((aligned (ALIGNMENT)))'; see the following section.
+
+
+File: gcc.info,  Node: Variable Attributes,  Next: Type Attributes,  Prev: Character Escapes,  Up: C Extensions
+
+Specifying Attributes of Variables
+==================================
+
+   The keyword `__attribute__' allows you to specify special attributes
+of variables or structure fields.  This keyword is followed by an
+attribute specification inside double parentheses.  Eight attributes
+are currently defined for variables: `aligned', `mode', `nocommon',
+`packed', `section', `transparent_union', `unused', and `weak'.  Other
+attributes are available for functions (*note Function Attributes::.)
+and for types (*note Type Attributes::.).
+
+   You may also specify attributes with `__' preceding and following
+each keyword.  This allows you to use them in header files without
+being concerned about a possible macro of the same name.  For example,
+you may use `__aligned__' instead of `aligned'.
+
+`aligned (ALIGNMENT)'
+     This attribute specifies a minimum alignment for the variable or
+     structure field, measured in bytes.  For example, the declaration:
+
+          int x __attribute__ ((aligned (16))) = 0;
+
+     causes the compiler to allocate the global variable `x' on a
+     16-byte boundary.  On a 68040, this could be used in conjunction
+     with an `asm' expression to access the `move16' instruction which
+     requires 16-byte aligned operands.
+
+     You can also specify the alignment of structure fields.  For
+     example, to create a double-word aligned `int' pair, you could
+     write:
+
+          struct foo { int x[2] __attribute__ ((aligned (8))); };
+
+     This is an alternative to creating a union with a `double' member
+     that forces the union to be double-word aligned.
+
+     It is not possible to specify the alignment of functions; the
+     alignment of functions is determined by the machine's requirements
+     and cannot be changed.  You cannot specify alignment for a typedef
+     name because such a name is just an alias, not a distinct type.
+
+     As in the preceding examples, you can explicitly specify the
+     alignment (in bytes) that you wish the compiler to use for a given
+     variable or structure field.  Alternatively, you can leave out the
+     alignment factor and just ask the compiler to align a variable or
+     field to the maximum useful alignment for the target machine you
+     are compiling for.  For example, you could write:
+
+          short array[3] __attribute__ ((aligned));
+
+     Whenever you leave out the alignment factor in an `aligned'
+     attribute specification, the compiler automatically sets the
+     alignment for the declared variable or field to the largest
+     alignment which is ever used for any data type on the target
+     machine you are compiling for.  Doing this can often make copy
+     operations more efficient, because the compiler can use whatever
+     instructions copy the biggest chunks of memory when performing
+     copies to or from the variables or fields that you have aligned
+     this way.
+
+     The `aligned' attribute can only increase the alignment; but you
+     can decrease it by specifying `packed' as well.  See below.
+
+     Note that the effectiveness of `aligned' attributes may be limited
+     by inherent limitations in your linker.  On many systems, the
+     linker is only able to arrange for variables to be aligned up to a
+     certain maximum alignment.  (For some linkers, the maximum
+     supported alignment may be very very small.)  If your linker is
+     only able to align variables up to a maximum of 8 byte alignment,
+     then specifying `aligned(16)' in an `__attribute__' will still
+     only provide you with 8 byte alignment.  See your linker
+     documentation for further information.
+
+`mode (MODE)'
+     This attribute specifies the data type for the
+     declaration--whichever type corresponds to the mode MODE.  This in
+     effect lets you request an integer or floating point type
+     according to its width.
+
+     You may also specify a mode of `byte' or `__byte__' to indicate
+     the mode corresponding to a one-byte integer, `word' or `__word__'
+     for the mode of a one-word integer, and `pointer' or `__pointer__'
+     for the mode used to represent pointers.
+
+`nocommon'
+     This attribute specifies requests GNU CC not to place a variable
+     "common" but instead to allocate space for it directly.  If you
+     specify the `-fno-common' flag, GNU CC will do this for all
+     variables.
+
+     Specifying the `nocommon' attribute for a variable provides an
+     initialization of zeros.  A variable may only be initialized in one
+     source file.
+
+`packed'
+     The `packed' attribute specifies that a variable or structure field
+     should have the smallest possible alignment--one byte for a
+     variable, and one bit for a field, unless you specify a larger
+     value with the `aligned' attribute.
+
+     Here is a structure in which the field `x' is packed, so that it
+     immediately follows `a':
+
+          struct foo
+          {
+            char a;
+            int x[2] __attribute__ ((packed));
+          };
+
+`section ("section-name")'
+     Normally, the compiler places the objects it generates in sections
+     like `data' and `bss'.  Sometimes, however, you need additional
+     sections, or you need certain particular variables to appear in
+     special sections, for example to map to special hardware.  The
+     `section' attribute specifies that a variable (or function) lives
+     in a particular section.  For example, this small program uses
+     several specific section names:
+
+          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
+          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
+          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
+          int init_data_copy __attribute__ ((section ("INITDATACOPY"))) = 0;
+          
+          main()
+          {
+            /* Initialize stack pointer */
+            init_sp (stack + sizeof (stack));
+          
+            /* Initialize initialized data */
+            memcpy (&init_data_copy, &data, &edata - &data);
+          
+            /* Turn on the serial ports */
+            init_duart (&a);
+            init_duart (&b);
+          }
+
+     Use the `section' attribute with an *initialized* definition of a
+     *global* variable, as shown in the example.  GNU CC issues a
+     warning and otherwise ignores the `section' attribute in
+     uninitialized variable declarations.
+
+     You may only use the `section' attribute with a fully initialized
+     global definition because of the way linkers work.  The linker
+     requires each object be defined once, with the exception that
+     uninitialized variables tentatively go in the `common' (or `bss')
+     section and can be multiply "defined".  You can force a variable
+     to be initialized with the `-fno-common' flag or the `nocommon'
+     attribute.
+
+     Some file formats do not support arbitrary sections so the
+     `section' attribute is not available on all platforms.  If you
+     need to map the entire contents of a module to a particular
+     section, consider using the facilities of the linker instead.
+
+`transparent_union'
+     This attribute, attached to a function argument variable which is a
+     union, means to pass the argument in the same way that the first
+     union member would be passed.  You can also use this attribute on a
+     `typedef' for a union data type; then it applies to all function
+     arguments with that type.
+
+`unused'
+     This attribute, attached to a variable, means that the variable is
+     meant to be possibly unused.  GNU CC will not produce a warning
+     for this variable.
+
+`weak'
+     The `weak' attribute is described in *Note Function Attributes::.
+
+   To specify multiple attributes, separate them by commas within the
+double parentheses: for example, `__attribute__ ((aligned (16),
+packed))'.
+
+
+File: gcc.info,  Node: Type Attributes,  Next: Alignment,  Prev: Variable Attributes,  Up: C Extensions
+
+Specifying Attributes of Types
+==============================
+
+   The keyword `__attribute__' allows you to specify special attributes
+of `struct' and `union' types when you define such types.  This keyword
+is followed by an attribute specification inside double parentheses.
+Three attributes are currently defined for types: `aligned', `packed',
+and `transparent_union'.  Other attributes are defined for functions
+(*note Function Attributes::.) and for variables (*note Variable
+Attributes::.).
+
+   You may also specify any one of these attributes with `__' preceding
+and following its keyword.  This allows you to use these attributes in
+header files without being concerned about a possible macro of the same
+name.  For example, you may use `__aligned__' instead of `aligned'.
+
+   You may specify the `aligned' and `transparent_union' attributes
+either in a `typedef' declaration or just past the closing curly brace
+of a complete enum, struct or union type *definition* and the `packed'
+attribute only past the closing brace of a definition.
+
+`aligned (ALIGNMENT)'
+     This attribute specifies a minimum alignment (in bytes) for
+     variables of the specified type.  For example, the declarations:
+
+          struct S { short f[3]; } __attribute__ ((aligned (8));
+          typedef int more_aligned_int __attribute__ ((aligned (8));
+
+     force the compiler to insure (as fas as it can) that each variable
+     whose type is `struct S' or `more_aligned_int' will be allocated
+     and aligned *at least* on a 8-byte boundary.  On a Sparc, having
+     all variables of type `struct S' aligned to 8-byte boundaries
+     allows the compiler to use the `ldd' and `std' (doubleword load and
+     store) instructions when copying one variable of type `struct S' to
+     another, thus improving run-time efficiency.
+
+     Note that the alignment of any given `struct' or `union' type is
+     required by the ANSI C standard to be at least a perfect multiple
+     of the lowest common multiple of the alignments of all of the
+     members of the `struct' or `union' in question.  This means that
+     you *can* effectively adjust the alignment of a `struct' or `union'
+     type by attaching an `aligned' attribute to any one of the members
+     of such a type, but the notation illustrated in the example above
+     is a more obvious, intuitive, and readable way to request the
+     compiler to adjust the alignment of an entire `struct' or `union'
+     type.
+
+     As in the preceding example, you can explicitly specify the
+     alignment (in bytes) that you wish the compiler to use for a given
+     `struct' or `union' type.  Alternatively, you can leave out the
+     alignment factor and just ask the compiler to align a type to the
+     maximum useful alignment for the target machine you are compiling
+     for.  For example, you could write:
+
+          struct S { short f[3]; } __attribute__ ((aligned));
+
+     Whenever you leave out the alignment factor in an `aligned'
+     attribute specification, the compiler automatically sets the
+     alignment for the type to the largest alignment which is ever used
+     for any data type on the target machine you are compiling for.
+     Doing this can often make copy operations more efficient, because
+     the compiler can use whatever instructions copy the biggest chunks
+     of memory when performing copies to or from the variables which
+     have types that you have aligned this way.
+
+     In the example above, if the size of each `short' is 2 bytes, then
+     the size of the entire `struct S' type is 6 bytes.  The smallest
+     power of two which is greater than or equal to that is 8, so the
+     compiler sets the alignment for the entire `struct S' type to 8
+     bytes.
+
+     Note that although you can ask the compiler to select a
+     time-efficient alignment for a given type and then declare only
+     individual stand-alone objects of that type, the compiler's
+     ability to select a time-efficient alignment is primarily useful
+     only when you plan to create arrays of variables having the
+     relevant (efficiently aligned) type.  If you declare or use arrays
+     of variables of an efficiently-aligned type, then it is likely
+     that your program will also be doing pointer arithmetic (or
+     subscripting, which amounts to the same thing) on pointers to the
+     relevant type, and the code that the compiler generates for these
+     pointer arithmetic operations will often be more efficient for
+     efficiently-aligned types than for other types.
+
+     The `aligned' attribute can only increase the alignment; but you
+     can decrease it by specifying `packed' as well.  See below.
+
+     Note that the effectiveness of `aligned' attributes may be limited
+     by inherent limitations in your linker.  On many systems, the
+     linker is only able to arrange for variables to be aligned up to a
+     certain maximum alignment.  (For some linkers, the maximum
+     supported alignment may be very very small.)  If your linker is
+     only able to align variables up to a maximum of 8 byte alignment,
+     then specifying `aligned(16)' in an `__attribute__' will still
+     only provide you with 8 byte alignment.  See your linker
+     documentation for further information.
+
+`packed'
+     This attribute, attached to an `enum', `struct', or `union' type
+     definition, specified that the minimum required memory be used to
+     represent the type.
+
+     Specifying this attribute for `struct' and `union' types is
+     equivalent to specifying the `packed' attribute on each of the
+     structure or union members.  Specifying the `-fshort-enums' flag
+     on the line is equivalent to specifying the `packed' attribute on
+     all `enum' definitions.
+
+     You may only specify this attribute after a closing curly brace on
+     an `enum' definition, not in a `typedef' declaration.
+
+`transparent_union'
+     This attribute, attached to a `union' type definition, indicates
+     that any variable having that union type should, if passed to a
+     function, be passed in the same way that the first union member
+     would be passed.  For example:
+
+          union foo
+          {
+            char a;
+            int x[2];
+          } __attribute__ ((transparent_union));
+
+   To specify multiple attributes, separate them by commas within the
+double parentheses: for example, `__attribute__ ((aligned (16),
+packed))'.
+
+
+File: gcc.info,  Node: Inline,  Next: Extended Asm,  Prev: Alignment,  Up: C Extensions
+
+An Inline Function is As Fast As a Macro
+========================================
+
+   By declaring a function `inline', you can direct GNU CC to integrate
+that function's code into the code for its callers.  This makes
+execution faster by eliminating the function-call overhead; in
+addition, if any of the actual argument values are constant, their known
+values may permit simplifications at compile time so that not all of the
+inline function's code needs to be included.  The effect on code size is
+less predictable; object code may be larger or smaller with function
+inlining, depending on the particular case.  Inlining of functions is an
+optimization and it really "works" only in optimizing compilation.  If
+you don't use `-O', no function is really inline.
+
+   To declare a function inline, use the `inline' keyword in its
+declaration, like this:
+
+     inline int
+     inc (int *a)
+     {
+       (*a)++;
+     }
+
+   (If you are writing a header file to be included in ANSI C programs,
+write `__inline__' instead of `inline'.  *Note Alternate Keywords::.)
+
+   You can also make all "simple enough" functions inline with the
+option `-finline-functions'.  Note that certain usages in a function
+definition can make it unsuitable for inline substitution.
+
+   Note that in C and Objective C, unlike C++, the `inline' keyword
+does not affect the linkage of the function.
+
+   GNU CC automatically inlines member functions defined within the
+class body of C++ programs even if they are not explicitly declared
+`inline'.  (You can override this with `-fno-default-inline'; *note
+Options Controlling C++ Dialect: C++ Dialect Options..)
+
+   When a function is both inline and `static', if all calls to the
+function are integrated into the caller, and the function's address is
+never used, then the function's own assembler code is never referenced.
+In this case, GNU CC does not actually output assembler code for the
+function, unless you specify the option `-fkeep-inline-functions'.
+Some calls cannot be integrated for various reasons (in particular,
+calls that precede the function's definition cannot be integrated, and
+neither can recursive calls within the definition).  If there is a
+nonintegrated call, then the function is compiled to assembler code as
+usual.  The function must also be compiled as usual if the program
+refers to its address, because that can't be inlined.
+
+   When an inline function is not `static', then the compiler must
+assume that there may be calls from other source files; since a global
+symbol can be defined only once in any program, the function must not
+be defined in the other source files, so the calls therein cannot be
+integrated.  Therefore, a non-`static' inline function is always
+compiled on its own in the usual fashion.
+
+   If you specify both `inline' and `extern' in the function
+definition, then the definition is used only for inlining.  In no case
+is the function compiled on its own, not even if you refer to its
+address explicitly.  Such an address becomes an external reference, as
+if you had only declared the function, and had not defined it.
+
+   This combination of `inline' and `extern' has almost the effect of a
+macro.  The way to use it is to put a function definition in a header
+file with these keywords, and put another copy of the definition
+(lacking `inline' and `extern') in a library file.  The definition in
+the header file will cause most calls to the function to be inlined.
+If any uses of the function remain, they will refer to the single copy
+in the library.
+
+   GNU C does not inline any functions when not optimizing.  It is not
+clear whether it is better to inline or not, in this case, but we found
+that a correct implementation when not optimizing was difficult.  So we
+did the easy thing, and turned it off.
+
+
+File: gcc.info,  Node: Extended Asm,  Next: Asm Labels,  Prev: Inline,  Up: C Extensions
+
+Assembler Instructions with C Expression Operands
+=================================================
+
+   In an assembler instruction using `asm', you can now specify the
+operands of the instruction using C expressions.  This means no more
+guessing which registers or memory locations will contain the data you
+want to use.
+
+   You must specify an assembler instruction template much like what
+appears in a machine description, plus an operand constraint string for
+each operand.
+
+   For example, here is how to use the 68881's `fsinx' instruction:
+
+     asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
+
+Here `angle' is the C expression for the input operand while `result'
+is that of the output operand.  Each has `"f"' as its operand
+constraint, saying that a floating point register is required.  The `='
+in `=f' indicates that the operand is an output; all output operands'
+constraints must use `='.  The constraints use the same language used
+in the machine description (*note Constraints::.).
+
+   Each operand is described by an operand-constraint string followed
+by the C expression in parentheses.  A colon separates the assembler
+template from the first output operand, and another separates the last
+output operand from the first input, if any.  Commas separate output
+operands and separate inputs.  The total number of operands is limited
+to ten or to the maximum number of operands in any instruction pattern
+in the machine description, whichever is greater.
+
+   If there are no output operands, and there are input operands, then
+there must be two consecutive colons surrounding the place where the
+output operands would go.
+
+   Output operand expressions must be lvalues; the compiler can check
+this.  The input operands need not be lvalues.  The compiler cannot
+check whether the operands have data types that are reasonable for the
+instruction being executed.  It does not parse the assembler
+instruction template and does not know what it means, or whether it is
+valid assembler input.  The extended `asm' feature is most often used
+for machine instructions that the compiler itself does not know exist.
+If the output expression cannot be directly addressed (for example, it
+is a bit field), your constraint must allow a register.  In that case,
+GNU CC will use the register as the output of the `asm', and then store
+that register into the output.
+
+   The output operands must be write-only; GNU CC will assume that the
+values in these operands before the instruction are dead and need not be
+generated.  Extended asm does not support input-output or read-write
+operands.  For this reason, the constraint character `+', which
+indicates such an operand, may not be used.
+
+   When the assembler instruction has a read-write operand, or an
+operand in which only some of the bits are to be changed, you must
+logically split its function into two separate operands, one input
+operand and one write-only output operand.  The connection between them
+is expressed by constraints which say they need to be in the same
+location when the instruction executes.  You can use the same C
+expression for both operands, or different expressions.  For example,
+here we write the (fictitious) `combine' instruction with `bar' as its
+read-only source operand and `foo' as its read-write destination:
+
+     asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
+
+The constraint `"0"' for operand 1 says that it must occupy the same
+location as operand 0.  A digit in constraint is allowed only in an
+input operand, and it must refer to an output operand.
+
+   Only a digit in the constraint can guarantee that one operand will
+be in the same place as another.  The mere fact that `foo' is the value
+of both operands is not enough to guarantee that they will be in the
+same place in the generated assembler code.  The following would not
+work:
+
+     asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
+
+   Various optimizations or reloading could cause operands 0 and 1 to
+be in different registers; GNU CC knows no reason not to do so.  For
+example, the compiler might find a copy of the value of `foo' in one
+register and use it for operand 1, but generate the output operand 0 in
+a different register (copying it afterward to `foo''s own address).  Of
+course, since the register for operand 1 is not even mentioned in the
+assembler code, the result will not work, but GNU CC can't tell that.
+
+   Some instructions clobber specific hard registers.  To describe
+this, write a third colon after the input operands, followed by the
+names of the clobbered hard registers (given as strings).  Here is a
+realistic example for the Vax:
+
+     asm volatile ("movc3 %0,%1,%2"
+                   : /* no outputs */
+                   : "g" (from), "g" (to), "g" (count)
+                   : "r0", "r1", "r2", "r3", "r4", "r5");
+
+   If you refer to a particular hardware register from the assembler
+code, then you will probably have to list the register after the third
+colon to tell the compiler that the register's value is modified.  In
+many assemblers, the register names begin with `%'; to produce one `%'
+in the assembler code, you must write `%%' in the input.
+
+   If your assembler instruction can alter the condition code register,
+add `cc' to the list of clobbered registers.  GNU CC on some machines
+represents the condition codes as a specific hardware register; `cc'
+serves to name this register.  On other machines, the condition code is
+handled differently, and specifying `cc' has no effect.  But it is
+valid no matter what the machine.
+
+   If your assembler instruction modifies memory in an unpredictable
+fashion, add `memory' to the list of clobbered registers.  This will
+cause GNU CC to not keep memory values cached in registers across the
+assembler instruction.
+
+   You can put multiple assembler instructions together in a single
+`asm' template, separated either with newlines (written as `\n') or with
+semicolons if the assembler allows such semicolons.  The GNU assembler
+allows semicolons and all Unix assemblers seem to do so.  The input
+operands are guaranteed not to use any of the clobbered registers, and
+neither will the output operands' addresses, so you can read and write
+the clobbered registers as many times as you like.  Here is an example
+of multiple instructions in a template; it assumes that the subroutine
+`_foo' accepts arguments in registers 9 and 10:
+
+     asm ("movl %0,r9;movl %1,r10;call _foo"
+          : /* no outputs */
+          : "g" (from), "g" (to)
+          : "r9", "r10");
+
+   Unless an output operand has the `&' constraint modifier, GNU CC may
+allocate it in the same register as an unrelated input operand, on the
+assumption that the inputs are consumed before the outputs are produced.
+This assumption may be false if the assembler code actually consists of
+more than one instruction.  In such a case, use `&' for each output
+operand that may not overlap an input.  *Note Modifiers::.
+
+   If you want to test the condition code produced by an assembler
+instruction, you must include a branch and a label in the `asm'
+construct, as follows:
+
+     asm ("clr %0;frob %1;beq 0f;mov #1,%0;0:"
+          : "g" (result)
+          : "g" (input));
+
+This assumes your assembler supports local labels, as the GNU assembler
+and most Unix assemblers do.
+
+   Speaking of labels, jumps from one `asm' to another are not
+supported.  The compiler's optimizers do not know about these jumps,
+and therefore they cannot take account of them when deciding how to
+optimize.
+
+   Usually the most convenient way to use these `asm' instructions is to
+encapsulate them in macros that look like functions.  For example,
+
+     #define sin(x)       \
+     ({ double __value, __arg = (x);   \
+        asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
+        __value; })
+
+Here the variable `__arg' is used to make sure that the instruction
+operates on a proper `double' value, and to accept only those arguments
+`x' which can convert automatically to a `double'.
+
+   Another way to make sure the instruction operates on the correct
+data type is to use a cast in the `asm'.  This is different from using a
+variable `__arg' in that it converts more different types.  For
+example, if the desired type were `int', casting the argument to `int'
+would accept a pointer with no complaint, while assigning the argument
+to an `int' variable named `__arg' would warn about using a pointer
+unless the caller explicitly casts it.
+
+   If an `asm' has output operands, GNU CC assumes for optimization
+purposes that the instruction has no side effects except to change the
+output operands.  This does not mean that instructions with a side
+effect cannot be used, but you must be careful, because the compiler
+may eliminate them if the output operands aren't used, or move them out
+of loops, or replace two with one if they constitute a common
+subexpression.  Also, if your instruction does have a side effect on a
+variable that otherwise appears not to change, the old value of the
+variable may be reused later if it happens to be found in a register.
+
+   You can prevent an `asm' instruction from being deleted, moved
+significantly, or combined, by writing the keyword `volatile' after the
+`asm'.  For example:
+
+     #define set_priority(x)  \
+     asm volatile ("set_priority %0": /* no outputs */ : "g" (x))
+
+An instruction without output operands will not be deleted or moved
+significantly, regardless, unless it is unreachable.
+
+   Note that even a volatile `asm' instruction can be moved in ways
+that appear insignificant to the compiler, such as across jump
+instructions.  You can't expect a sequence of volatile `asm'
+instructions to remain perfectly consecutive.  If you want consecutive
+output, use a single `asm'.
+
+   It is a natural idea to look for a way to give access to the
+condition code left by the assembler instruction.  However, when we
+attempted to implement this, we found no way to make it work reliably.
+The problem is that output operands might need reloading, which would
+result in additional following "store" instructions.  On most machines,
+these instructions would alter the condition code before there was time
+to test it.  This problem doesn't arise for ordinary "test" and
+"compare" instructions because they don't have any output operands.
+
+   If you are writing a header file that should be includable in ANSI C
+programs, write `__asm__' instead of `asm'.  *Note Alternate Keywords::.
+