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<h4 class="subsection">3.17.31 Nios II Options</h4>
<p><a name="index-Nios-II-options-2135"></a><a name="index-Altera-Nios-II-options-2136"></a>
These are the options defined for the Altera Nios II processor.
<dl>
<dt><code>-G </code><var>num</var><dd><a name="index-G-2137"></a><a name="index-smaller-data-references-2138"></a>Put global and static objects less than or equal to <var>num</var> bytes
into the small data or BSS sections instead of the normal data or BSS
sections. The default value of <var>num</var> is 8.
<br><dt><code>-mgpopt=</code><var>option</var><br><dt><code>-mgpopt</code><dt><code>-mno-gpopt</code><dd><a name="index-mgpopt-2139"></a><a name="index-mno_002dgpopt-2140"></a>Generate (do not generate) GP-relative accesses. The following
<var>option</var> names are recognized:
<dl>
<dt>‘<samp><span class="samp">none</span></samp>’<dd>Do not generate GP-relative accesses.
<br><dt>‘<samp><span class="samp">local</span></samp>’<dd>Generate GP-relative accesses for small data objects that are not
external or weak. Also use GP-relative addressing for objects that
have been explicitly placed in a small data section via a <code>section</code>
attribute.
<br><dt>‘<samp><span class="samp">global</span></samp>’<dd>As for ‘<samp><span class="samp">local</span></samp>’, but also generate GP-relative accesses for
small data objects that are external or weak. If you use this option,
you must ensure that all parts of your program (including libraries) are
compiled with the same <samp><span class="option">-G</span></samp> setting.
<br><dt>‘<samp><span class="samp">data</span></samp>’<dd>Generate GP-relative accesses for all data objects in the program. If you
use this option, the entire data and BSS segments
of your program must fit in 64K of memory and you must use an appropriate
linker script to allocate them within the addressible range of the
global pointer.
<br><dt>‘<samp><span class="samp">all</span></samp>’<dd>Generate GP-relative addresses for function pointers as well as data
pointers. If you use this option, the entire text, data, and BSS segments
of your program must fit in 64K of memory and you must use an appropriate
linker script to allocate them within the addressible range of the
global pointer.
</dl>
<p><samp><span class="option">-mgpopt</span></samp> is equivalent to <samp><span class="option">-mgpopt=local</span></samp>, and
<samp><span class="option">-mno-gpopt</span></samp> is equivalent to <samp><span class="option">-mgpopt=none</span></samp>.
<p>The default is <samp><span class="option">-mgpopt</span></samp> except when <samp><span class="option">-fpic</span></samp> or
<samp><span class="option">-fPIC</span></samp> is specified to generate position-independent code.
Note that the Nios II ABI does not permit GP-relative accesses from
shared libraries.
<p>You may need to specify <samp><span class="option">-mno-gpopt</span></samp> explicitly when building
programs that include large amounts of small data, including large
GOT data sections. In this case, the 16-bit offset for GP-relative
addressing may not be large enough to allow access to the entire
small data section.
<br><dt><code>-mel</code><dt><code>-meb</code><dd><a name="index-mel-2141"></a><a name="index-meb-2142"></a>Generate little-endian (default) or big-endian (experimental) code,
respectively.
<br><dt><code>-mbypass-cache</code><dt><code>-mno-bypass-cache</code><dd><a name="index-mno_002dbypass_002dcache-2143"></a><a name="index-mbypass_002dcache-2144"></a>Force all load and store instructions to always bypass cache by
using I/O variants of the instructions. The default is not to
bypass the cache.
<br><dt><code>-mno-cache-volatile</code><dt><code>-mcache-volatile</code><dd><a name="index-mcache_002dvolatile-2145"></a><a name="index-mno_002dcache_002dvolatile-2146"></a>Volatile memory access bypass the cache using the I/O variants of
the load and store instructions. The default is not to bypass the cache.
<br><dt><code>-mno-fast-sw-div</code><dt><code>-mfast-sw-div</code><dd><a name="index-mno_002dfast_002dsw_002ddiv-2147"></a><a name="index-mfast_002dsw_002ddiv-2148"></a>Do not use table-based fast divide for small numbers. The default
is to use the fast divide at <samp><span class="option">-O3</span></samp> and above.
<br><dt><code>-mno-hw-mul</code><dt><code>-mhw-mul</code><dt><code>-mno-hw-mulx</code><dt><code>-mhw-mulx</code><dt><code>-mno-hw-div</code><dt><code>-mhw-div</code><dd><a name="index-mno_002dhw_002dmul-2149"></a><a name="index-mhw_002dmul-2150"></a><a name="index-mno_002dhw_002dmulx-2151"></a><a name="index-mhw_002dmulx-2152"></a><a name="index-mno_002dhw_002ddiv-2153"></a><a name="index-mhw_002ddiv-2154"></a>Enable or disable emitting <code>mul</code>, <code>mulx</code> and <code>div</code> family of
instructions by the compiler. The default is to emit <code>mul</code>
and not emit <code>div</code> and <code>mulx</code>.
<br><dt><code>-mcustom-</code><var>insn</var><code>=</code><var>N</var><dt><code>-mno-custom-</code><var>insn</var><dd><a name="index-mcustom_002d_0040var_007binsn_007d-2155"></a><a name="index-mno_002dcustom_002d_0040var_007binsn_007d-2156"></a>Each <samp><span class="option">-mcustom-</span><var>insn</var><span class="option">=</span><var>N</var></samp> option enables use of a
custom instruction with encoding <var>N</var> when generating code that uses
<var>insn</var>. For example, <samp><span class="option">-mcustom-fadds=253</span></samp> generates custom
instruction 253 for single-precision floating-point add operations instead
of the default behavior of using a library call.
<p>The following values of <var>insn</var> are supported. Except as otherwise
noted, floating-point operations are expected to be implemented with
normal IEEE 754 semantics and correspond directly to the C operators or the
equivalent GCC built-in functions (see <a href="Other-Builtins.html#Other-Builtins">Other Builtins</a>).
<p>Single-precision floating point:
<dl>
<dt>‘<samp><span class="samp">fadds</span></samp>’, ‘<samp><span class="samp">fsubs</span></samp>’, ‘<samp><span class="samp">fdivs</span></samp>’, ‘<samp><span class="samp">fmuls</span></samp>’<dd>Binary arithmetic operations.
<br><dt>‘<samp><span class="samp">fnegs</span></samp>’<dd>Unary negation.
<br><dt>‘<samp><span class="samp">fabss</span></samp>’<dd>Unary absolute value.
<br><dt>‘<samp><span class="samp">fcmpeqs</span></samp>’, ‘<samp><span class="samp">fcmpges</span></samp>’, ‘<samp><span class="samp">fcmpgts</span></samp>’, ‘<samp><span class="samp">fcmples</span></samp>’, ‘<samp><span class="samp">fcmplts</span></samp>’, ‘<samp><span class="samp">fcmpnes</span></samp>’<dd>Comparison operations.
<br><dt>‘<samp><span class="samp">fmins</span></samp>’, ‘<samp><span class="samp">fmaxs</span></samp>’<dd>Floating-point minimum and maximum. These instructions are only
generated if <samp><span class="option">-ffinite-math-only</span></samp> is specified.
<br><dt>‘<samp><span class="samp">fsqrts</span></samp>’<dd>Unary square root operation.
<br><dt>‘<samp><span class="samp">fcoss</span></samp>’, ‘<samp><span class="samp">fsins</span></samp>’, ‘<samp><span class="samp">ftans</span></samp>’, ‘<samp><span class="samp">fatans</span></samp>’, ‘<samp><span class="samp">fexps</span></samp>’, ‘<samp><span class="samp">flogs</span></samp>’<dd>Floating-point trigonometric and exponential functions. These instructions
are only generated if <samp><span class="option">-funsafe-math-optimizations</span></samp> is also specified.
</dl>
<p>Double-precision floating point:
<dl>
<dt>‘<samp><span class="samp">faddd</span></samp>’, ‘<samp><span class="samp">fsubd</span></samp>’, ‘<samp><span class="samp">fdivd</span></samp>’, ‘<samp><span class="samp">fmuld</span></samp>’<dd>Binary arithmetic operations.
<br><dt>‘<samp><span class="samp">fnegd</span></samp>’<dd>Unary negation.
<br><dt>‘<samp><span class="samp">fabsd</span></samp>’<dd>Unary absolute value.
<br><dt>‘<samp><span class="samp">fcmpeqd</span></samp>’, ‘<samp><span class="samp">fcmpged</span></samp>’, ‘<samp><span class="samp">fcmpgtd</span></samp>’, ‘<samp><span class="samp">fcmpled</span></samp>’, ‘<samp><span class="samp">fcmpltd</span></samp>’, ‘<samp><span class="samp">fcmpned</span></samp>’<dd>Comparison operations.
<br><dt>‘<samp><span class="samp">fmind</span></samp>’, ‘<samp><span class="samp">fmaxd</span></samp>’<dd>Double-precision minimum and maximum. These instructions are only
generated if <samp><span class="option">-ffinite-math-only</span></samp> is specified.
<br><dt>‘<samp><span class="samp">fsqrtd</span></samp>’<dd>Unary square root operation.
<br><dt>‘<samp><span class="samp">fcosd</span></samp>’, ‘<samp><span class="samp">fsind</span></samp>’, ‘<samp><span class="samp">ftand</span></samp>’, ‘<samp><span class="samp">fatand</span></samp>’, ‘<samp><span class="samp">fexpd</span></samp>’, ‘<samp><span class="samp">flogd</span></samp>’<dd>Double-precision trigonometric and exponential functions. These instructions
are only generated if <samp><span class="option">-funsafe-math-optimizations</span></samp> is also specified.
</dl>
<p>Conversions:
<dl>
<dt>‘<samp><span class="samp">fextsd</span></samp>’<dd>Conversion from single precision to double precision.
<br><dt>‘<samp><span class="samp">ftruncds</span></samp>’<dd>Conversion from double precision to single precision.
<br><dt>‘<samp><span class="samp">fixsi</span></samp>’, ‘<samp><span class="samp">fixsu</span></samp>’, ‘<samp><span class="samp">fixdi</span></samp>’, ‘<samp><span class="samp">fixdu</span></samp>’<dd>Conversion from floating point to signed or unsigned integer types, with
truncation towards zero.
<br><dt>‘<samp><span class="samp">round</span></samp>’<dd>Conversion from single-precision floating point to signed integer,
rounding to the nearest integer and ties away from zero.
This corresponds to the <code>__builtin_lroundf</code> function when
<samp><span class="option">-fno-math-errno</span></samp> is used.
<br><dt>‘<samp><span class="samp">floatis</span></samp>’, ‘<samp><span class="samp">floatus</span></samp>’, ‘<samp><span class="samp">floatid</span></samp>’, ‘<samp><span class="samp">floatud</span></samp>’<dd>Conversion from signed or unsigned integer types to floating-point types.
</dl>
<p>In addition, all of the following transfer instructions for internal
registers X and Y must be provided to use any of the double-precision
floating-point instructions. Custom instructions taking two
double-precision source operands expect the first operand in the
64-bit register X. The other operand (or only operand of a unary
operation) is given to the custom arithmetic instruction with the
least significant half in source register <var>src1</var> and the most
significant half in <var>src2</var>. A custom instruction that returns a
double-precision result returns the most significant 32 bits in the
destination register and the other half in 32-bit register Y.
GCC automatically generates the necessary code sequences to write
register X and/or read register Y when double-precision floating-point
instructions are used.
<dl>
<dt>‘<samp><span class="samp">fwrx</span></samp>’<dd>Write <var>src1</var> into the least significant half of X and <var>src2</var> into
the most significant half of X.
<br><dt>‘<samp><span class="samp">fwry</span></samp>’<dd>Write <var>src1</var> into Y.
<br><dt>‘<samp><span class="samp">frdxhi</span></samp>’, ‘<samp><span class="samp">frdxlo</span></samp>’<dd>Read the most or least (respectively) significant half of X and store it in
<var>dest</var>.
<br><dt>‘<samp><span class="samp">frdy</span></samp>’<dd>Read the value of Y and store it into <var>dest</var>.
</dl>
<p>Note that you can gain more local control over generation of Nios II custom
instructions by using the <code>target("custom-</code><var>insn</var><code>=</code><var>N</var><code>")</code>
and <code>target("no-custom-</code><var>insn</var><code>")</code> function attributes
(see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>)
or pragmas (see <a href="Function-Specific-Option-Pragmas.html#Function-Specific-Option-Pragmas">Function Specific Option Pragmas</a>).
<br><dt><code>-mcustom-fpu-cfg=</code><var>name</var><dd><a name="index-mcustom_002dfpu_002dcfg-2157"></a>
This option enables a predefined, named set of custom instruction encodings
(see <samp><span class="option">-mcustom-</span><var>insn</var></samp> above).
Currently, the following sets are defined:
<p><samp><span class="option">-mcustom-fpu-cfg=60-1</span></samp> is equivalent to:
<pre class="smallexample"> -mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-fsingle-precision-constant
</pre>
<p><samp><span class="option">-mcustom-fpu-cfg=60-2</span></samp> is equivalent to:
<pre class="smallexample"> -mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant
</pre>
<p><samp><span class="option">-mcustom-fpu-cfg=72-3</span></samp> is equivalent to:
<pre class="smallexample"> -mcustom-floatus=243
-mcustom-fixsi=244
-mcustom-floatis=245
-mcustom-fcmpgts=246
-mcustom-fcmples=249
-mcustom-fcmpeqs=250
-mcustom-fcmpnes=251
-mcustom-fmuls=252
-mcustom-fadds=253
-mcustom-fsubs=254
-mcustom-fdivs=255
-fsingle-precision-constant
</pre>
<p>Custom instruction assignments given by individual
<samp><span class="option">-mcustom-</span><var>insn</var><span class="option">=</span></samp> options override those given by
<samp><span class="option">-mcustom-fpu-cfg=</span></samp>, regardless of the
order of the options on the command line.
<p>Note that you can gain more local control over selection of a FPU
configuration by using the <code>target("custom-fpu-cfg=</code><var>name</var><code>")</code>
function attribute (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>)
or pragma (see <a href="Function-Specific-Option-Pragmas.html#Function-Specific-Option-Pragmas">Function Specific Option Pragmas</a>).
</dl>
<p>These additional ‘<samp><span class="samp">-m</span></samp>’ options are available for the Altera Nios II
ELF (bare-metal) target:
<dl>
<dt><code>-mhal</code><dd><a name="index-mhal-2158"></a>Link with HAL BSP. This suppresses linking with the GCC-provided C runtime
startup and termination code, and is typically used in conjunction with
<samp><span class="option">-msys-crt0=</span></samp> to specify the location of the alternate startup code
provided by the HAL BSP.
<br><dt><code>-msmallc</code><dd><a name="index-msmallc-2159"></a>Link with a limited version of the C library, <samp><span class="option">-lsmallc</span></samp>, rather than
Newlib.
<br><dt><code>-msys-crt0=</code><var>startfile</var><dd><a name="index-msys_002dcrt0-2160"></a><var>startfile</var> is the file name of the startfile (crt0) to use
when linking. This option is only useful in conjunction with <samp><span class="option">-mhal</span></samp>.
<br><dt><code>-msys-lib=</code><var>systemlib</var><dd><a name="index-msys_002dlib-2161"></a><var>systemlib</var> is the library name of the library that provides
low-level system calls required by the C library,
e.g. <code>read</code> and <code>write</code>.
This option is typically used to link with a library provided by a HAL BSP.
</dl>
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