[Ada] Document entries of the target parametrization file

2018-08-21  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Document entries of the target parametrization file.
	* gnat_ugn.texi: Regenerate.

From-SVN: r263725

gcc/ada/ChangeLog

+2018-08-21  Yannick Moy  <moy@adacore.com>
+
+	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
+	Document entries of the target parametrization file.
+	* gnat_ugn.texi: Regenerate.
+
 2018-08-21  Ed Schonberg  <schonberg@adacore.com>
 
 	* sem_attr.adb: Set scope of elaboration flag for 'Access.

gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst

@@ -1692,13 +1692,44 @@ Alphabetical List of All Switches
     Maximum_Alignment          : Pos; -- Maximum permitted alignment
     Max_Unaligned_Field        : Pos; -- Maximum size for unaligned bit field
     Pointer_Size               : Pos; -- System.Address'Size
-    Short_Enums                : Nat; -- Short foreign convention enums?
+    Short_Enums                : Nat; -- Foreign enums use short size?
     Short_Size                 : Pos; -- Standard.Short_Integer'Size
     Strict_Alignment           : Nat; -- Strict alignment?
     System_Allocator_Alignment : Nat; -- Alignment for malloc calls
     Wchar_T_Size               : Pos; -- Interfaces.C.wchar_t'Size
     Words_BE                   : Nat; -- Words stored big-endian?
 
+  ``Bits_Per_Unit`` is the number of bits in a storage unit, the equivalent of
+  GCC macro ``BITS_PER_UNIT`` documented as follows: `Define this macro to be
+  the number of bits in an addressable storage unit (byte); normally 8.`
+
+  ``Bits_Per_Word`` is the number of bits in a machine word, the equivalent of
+  GCC macro ``BITS_PER_WORD`` documented as follows: `Number of bits in a word;
+  normally 32.`
+
+  ``Double_Scalar_Alignment`` is the alignment for a scalar whose size is two
+  machine words. It should be the same as the alignment for C ``long_long`` on
+  most targets.
+
+  ``Maximum_Alignment`` is the maximum alignment that the compiler might choose
+  by default for a type or object, which is also the maximum alignment that can
+  be specified in GNAT. It is computed for GCC backends as ``BIGGEST_ALIGNMENT
+  / BITS_PER_UNIT`` where GCC macro ``BIGGEST_ALIGNMENT`` is documented as
+  follows: `Biggest alignment that any data type can require on this machine,
+  in bits.`
+
+  ``Max_Unaligned_Field`` is the maximum size for unaligned bit field, which is
+  64 for the majority of GCC targets (but can be different on some targets like
+  AAMP).
+
+  ``Strict_Alignment`` is the equivalent of GCC macro ``STRICT_ALIGNMENT``
+  documented as follows: `Define this macro to be the value 1 if instructions
+  will fail to work if given data not on the nominal alignment. If instructions
+  will merely go slower in that case, define this macro as 0.`
+
+  ``System_Allocator_Alignment`` is the guaranteed alignment of data returned
+  by calls to ``malloc``.
+
 
   The format of the input file is as follows. First come the values of
   the variables defined above, with one line per value:

gcc/ada/gnat_ugn.texi

@@ -21,7 +21,7 @@
 
 @copying
 @quotation
-GNAT User's Guide for Native Platforms , Aug 17, 2018
+GNAT User's Guide for Native Platforms , Aug 20, 2018
 
 AdaCore
 
@@ -9429,7 +9429,7 @@ Long_Size                  : Pos; -- Standard.Long_Integer'Size
 Maximum_Alignment          : Pos; -- Maximum permitted alignment
 Max_Unaligned_Field        : Pos; -- Maximum size for unaligned bit field
 Pointer_Size               : Pos; -- System.Address'Size
-Short_Enums                : Nat; -- Short foreign convention enums?
+Short_Enums                : Nat; -- Foreign enums use short size?
 Short_Size                 : Pos; -- Standard.Short_Integer'Size
 Strict_Alignment           : Nat; -- Strict alignment?
 System_Allocator_Alignment : Nat; -- Alignment for malloc calls
@@ -9437,6 +9437,32 @@ Wchar_T_Size               : Pos; -- Interfaces.C.wchar_t'Size
 Words_BE                   : Nat; -- Words stored big-endian?
 @end example
 
+@code{Bits_Per_Unit} is the number of bits in a storage unit, the equivalent of
+GCC macro @code{BITS_PER_UNIT} documented as follows: @cite{Define this macro to be the number of bits in an addressable storage unit (byte); normally 8.}
+
+@code{Bits_Per_Word} is the number of bits in a machine word, the equivalent of
+GCC macro @code{BITS_PER_WORD} documented as follows: @cite{Number of bits in a word; normally 32.}
+
+@code{Double_Scalar_Alignment} is the alignment for a scalar whose size is two
+machine words. It should be the same as the alignment for C @code{long_long} on
+most targets.
+
+@code{Maximum_Alignment} is the maximum alignment that the compiler might choose
+by default for a type or object, which is also the maximum alignment that can
+be specified in GNAT. It is computed for GCC backends as @code{BIGGEST_ALIGNMENT
+/ BITS_PER_UNIT} where GCC macro @code{BIGGEST_ALIGNMENT} is documented as
+follows: @cite{Biggest alignment that any data type can require on this machine@comma{} in bits.}
+
+@code{Max_Unaligned_Field} is the maximum size for unaligned bit field, which is
+64 for the majority of GCC targets (but can be different on some targets like
+AAMP).
+
+@code{Strict_Alignment} is the equivalent of GCC macro @code{STRICT_ALIGNMENT}
+documented as follows: @cite{Define this macro to be the value 1 if instructions will fail to work if given data not on the nominal alignment. If instructions will merely go slower in that case@comma{} define this macro as 0.}
+
+@code{System_Allocator_Alignment} is the guaranteed alignment of data returned
+by calls to @code{malloc}.
+
 The format of the input file is as follows. First come the values of
 the variables defined above, with one line per value: