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<H1> 13.8 Machine Code Insertions</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I4582"></A> A machine code insertion
can be achieved by a call to a subprogram whose <FONT FACE="Arial, Helvetica">sequence_of_statements</FONT>
contains <FONT FACE="Arial, Helvetica">code_statement</FONT>s.] </DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">code_statement<A NAME="I4583"></A>
::= </FONT><A NAME="I4584"></A><FONT FACE="Arial, Helvetica">qualified_expression</FONT>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented">A <FONT FACE="Arial, Helvetica">code_statement</FONT>
is only allowed in the <FONT FACE="Arial, Helvetica">handled_sequence_of_statements</FONT>
of a <FONT FACE="Arial, Helvetica">subprogram_body</FONT>. If a <FONT FACE="Arial, Helvetica">subprogram_body</FONT>
contains any <FONT FACE="Arial, Helvetica">code_statement</FONT>s, then
within this <FONT FACE="Arial, Helvetica">subprogram_body</FONT> the
only allowed form of <FONT FACE="Arial, Helvetica">statement</FONT> is
a <FONT FACE="Arial, Helvetica">code_statement</FONT> (labeled or not),
the only allowed <FONT FACE="Arial, Helvetica">declarative_item</FONT>s
are <FONT FACE="Arial, Helvetica">use_clause</FONT>s, and no <FONT FACE="Arial, Helvetica">exception_handler</FONT>
is allowed (<FONT FACE="Arial, Helvetica">comment</FONT>s and <FONT FACE="Arial, Helvetica">pragma</FONT>s
are allowed as usual). </DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4585"></A>The <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
is expected to be of any type. </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> The <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
shall be of a type declared in package System.Machine_Code. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>This includes
types declared in children of System.Machine_Code. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">code_statement</FONT>
shall appear only within the scope of a <FONT FACE="Arial, Helvetica">with_clause</FONT>
that mentions package System.Machine_Code. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Note that
this is not a note; without this rule, it would be possible to write
machine code in compilation units which depend on System.Machine_Code
only indirectly. </FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4586"></A><A NAME="I4587"></A><A NAME="I4588"></A><A NAME="I4589"></A>The
contents of the library package System.Machine_Code (if provided) are
implementation defined. The meaning of <FONT FACE="Arial, Helvetica">code_statement</FONT>s
is implementation defined. [Typically, each <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
represents a machine instruction or assembly directive.] </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>For example,
an instruction might be a record with an Op_Code component and other
components for the operands. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
contents of the visible part of package System.Machine_Code, and the
meaning of <FONT FACE="Arial, Helvetica">code_statement</FONT>s.</FONT></DIV>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> An implementation may place restrictions on <FONT FACE="Arial, Helvetica">code_statement</FONT>s.
An implementation is not required to provide package System.Machine_Code.
</DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>15 An implementation may
provide implementation-defined pragmas specifying register conventions
and calling conventions.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>16 Machine code functions
are exempt from the rule that a <FONT FACE="Arial, Helvetica">return_statement</FONT>
is required. In fact, <FONT FACE="Arial, Helvetica">return_statement</FONT>s
are forbidden, since only <FONT FACE="Arial, Helvetica">code_statement</FONT>s
are allowed. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The idea is
that the author of a machine code subprogram knows the calling conventions,
and refers to parameters and results accordingly. The implementation
should document where to put the result of a machine code function, for
example, ``Scalar results are returned in register 0.'' </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>17 Intrinsic subprograms
(see <A HREF="AA-6-3-1.html">6.3.1</A>, ``<A HREF="AA-6-3-1.html">Conformance
Rules</A>'') can also be used to achieve machine code insertions. Interface
to assembly language can be achieved using the features in <A HREF="AA-B.html">Annex
B</A>, ``<A HREF="AA-B.html">Interface to Other Languages</A>''. </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Example of a
code statement:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples"><TT>M : Mask;<BR>
<B>procedure</B> Set_Mask; <B>pragma</B> Inline(Set_Mask);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Set_Mask <B>is</B><BR>
<B>use</B> System.Machine_Code; --<I> assume ``<B>with</B> System.Machine_Code;'' appears somewhere above</I><BR>
<B>begin</B><BR>
SI_Format'(Code => SSM, B => M'Base_Reg, D => M'Disp);<BR>
--<I> Base_Reg and Disp are implementation-defined attributes</I><BR>
<B>end</B> Set_Mask;</TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>14.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I4590"></A>Machine code
functions are allowed in Ada 95; in Ada 83, only procedures were allowed.
</FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>14.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The syntax for <FONT FACE="Arial, Helvetica">code_statement</FONT>
is changed to say ``<FONT FACE="Arial, Helvetica">qualified_expression</FONT>''
instead of ``<A NAME="I4591"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT>'<A NAME="I4592"></A><FONT FACE="Arial, Helvetica">record_aggregate</FONT>''.
Requiring the type of each instruction to be a record type is overspecification.
</FONT></DIV>
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