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<head>
<title>env target and nesc1</title>
</head>
<body>
The <tt>env</tt> target allows the nesC compiler to be configured for a new
platform without requiring source code changes. It allows specification of
a target's data layout rules.
<blockquote>If <tt>-fnesc-target=env</tt> option is passed to <tt>nescc</tt>,
the compilation uses
a machine specification described in the environment variable
<tt>NESC_MACHINE</tt>, such as <blockquote><tt>export
NESC_MACHINE="long_double=8,4"</tt></blockquote> A
particular order to the keynames in <tt>NESC_MACHINE</tt> is not necessary.
The table below is a complete list of possible key names for
<tt>NESC_MACHINE</tt>, a short description of their values, and their
default if unspecified: <blockquote>
<table border=1 cellpadding=2 cellspacing=0>
<tr><th>Keyname <th>Value <th>Default
<tr><td>pcc_bitfield_type_matters <td>bool <td>false
<tr><td>empty_field_boundary <td>bit align <td>8
<tr><td>structure_size_boundary <td>bit align <td>8
<tr><td>word_size <td>size <td>1
<tr><td>pointer <td>size,align <td>2,1
<tr><td>float <td>size,align <td>4,1
<tr><td>double <td>size,align <td>4,1
<tr><td>long_double <td>size,align <td>4,1
<tr><td>short <td>size,align <td>2,1
<tr><td>int <td>size,align <td>2,1
<tr><td>long <td>size,align <td>4,1
<tr><td>long_long <td>size,align <td>8,1
<tr><td>int1248_align <td>align,align,align,align <td>1,1,1,1
<tr><td>wchar_size_size <td>size,size <td>2,2
<tr><td>char_wchar_signed <td>bool,bool <td>true,true
<tr><td>async_functions <td>string <td>empty
</table>
</blockquote>
For reference and easy cut+paste, here is the full default specification for
<tt>NESC_MACHINE</tt>: <blockquote><tt>export
NESC_MACHINE="pcc_bitfield_type_matters=false word_size=1 pointer=2,1 float=4,1
double=4,1 long_double=4,1 short=2,1 int=2,1 long=4,1 long_long=8,1
int1248_align=1,1,1,1 wchar_size_size=2,2 char_wchar_signed=true,true
empty_field_boundary=8 structure_size_boundary=8"
</tt></blockquote>
The curiously named wchar_size_size is the sizes of <code>wchar_t</code>
and <code>size_t</code> respectively. See the gcc internal documentation
(`<code>info gccint</code>') for more information on
pcc_bitfield_type_matters, empty_field_boundary and
structure_size_boundary.
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