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PR other/69477 - attribute aligned documentation misleading

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gcc/ChangeLog:
2016-01-26  Martin Sebor  <msebor@redhat.com>

	PR other/69477
	* doc/extend.texi (Common Type Attributes): Move text that talks about
	attribute packed from attribute aligned to the section discussing
	the former attribute for clarity.

From-SVN: r232840
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Martin Sebor 2016-01-26 17:44:38 +00:00 • committed by Martin Sebor
parent ffc445f486
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2 changed files with 40 additions and 33 deletions
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@ -1,3 +1,10 @@
2016-01-26 Martin Sebor <msebor@redhat.com>
PR other/69477
* doc/extend.texi (Common Type Attributes): Move text that talks about
attribute packed from attribute aligned to the section discussing
the former attribute for clarity.
2016-01-26 Richard Henderson <rth@redhat.com>
PR middle-end/60908

66
gcc/doc/extend.texi
View file

@ -6307,9 +6307,6 @@ relevant type, and the code that the compiler generates for these
pointer arithmetic operations is often more efficient for
efficiently-aligned types than for other types.
The @code{aligned} attribute can only increase the alignment; but you
can decrease it by specifying @code{packed} as well. See below.
Note that the effectiveness of @code{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
@ -6319,36 +6316,8 @@ up to a maximum of 8-byte alignment, then specifying @code{aligned(16)}
in an @code{__attribute__} still only provides you with 8-byte
alignment. See your linker documentation for further information.
@opindex fshort-enums
Specifying this attribute for @code{struct} and @code{union} types is
equivalent to specifying the @code{packed} attribute on each of the
structure or union members. Specifying the @option{-fshort-enums}
flag on the line is equivalent to specifying the @code{packed}
attribute on all @code{enum} definitions.
In the following example @code{struct my_packed_struct}'s members are
packed closely together, but the internal layout of its @code{s} member
is not packed---to do that, @code{struct my_unpacked_struct} needs to
be packed too.
@smallexample
struct my_unpacked_struct
@{
char c;
int i;
@};
struct __attribute__ ((__packed__)) my_packed_struct
@{
char c;
int i;
struct my_unpacked_struct s;
@};
@end smallexample
You may only specify this attribute on the definition of an @code{enum},
@code{struct} or @code{union}, not on a @code{typedef} that does not
also define the enumerated type, structure or union.
The @code{aligned} attribute can only increase alignment. Alignment
can be decreased by specifying the @code{packed} attribute. See below.
@item bnd_variable_size
@cindex @code{bnd_variable_size} type attribute
@ -6476,6 +6445,37 @@ of the structure or union is placed to minimize the memory required. When
attached to an @code{enum} definition, it indicates that the smallest
integral type should be used.
@opindex fshort-enums
Specifying the @code{packed} attribute for @code{struct} and @code{union}
types is equivalent to specifying the @code{packed} attribute on each
of the structure or union members. Specifying the @option{-fshort-enums}
flag on the command line is equivalent to specifying the @code{packed}
attribute on all @code{enum} definitions.
In the following example @code{struct my_packed_struct}'s members are
packed closely together, but the internal layout of its @code{s} member
is not packed---to do that, @code{struct my_unpacked_struct} needs to
be packed too.
@smallexample
struct my_unpacked_struct
@{
char c;
int i;
@};
struct __attribute__ ((__packed__)) my_packed_struct
@{
char c;
int i;
struct my_unpacked_struct s;
@};
@end smallexample
You may only specify the @code{packed} attribute attribute on the definition
of an @code{enum}, @code{struct} or @code{union}, not on a @code{typedef}
that does not also define the enumerated type, structure or union.
@item scalar_storage_order ("@var{endianness}")
@cindex @code{scalar_storage_order} type attribute
When attached to a @code{union} or a @code{struct}, this attribute sets