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<h4 class="subsection">3.17.4 ARM Options</h4>
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<p><a name="index-ARM-options-1393"></a>
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These ‘<samp><span class="samp">-m</span></samp>’ options are defined for the ARM port:
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<dl>
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<dt><code>-mabi=</code><var>name</var><dd><a name="index-mabi-1394"></a>Generate code for the specified ABI. Permissible values are: ‘<samp><span class="samp">apcs-gnu</span></samp>’,
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‘<samp><span class="samp">atpcs</span></samp>’, ‘<samp><span class="samp">aapcs</span></samp>’, ‘<samp><span class="samp">aapcs-linux</span></samp>’ and ‘<samp><span class="samp">iwmmxt</span></samp>’.
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<br><dt><code>-mapcs-frame</code><dd><a name="index-mapcs_002dframe-1395"></a>Generate a stack frame that is compliant with the ARM Procedure Call
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Standard for all functions, even if this is not strictly necessary for
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correct execution of the code. Specifying <samp><span class="option">-fomit-frame-pointer</span></samp>
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with this option causes the stack frames not to be generated for
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leaf functions. The default is <samp><span class="option">-mno-apcs-frame</span></samp>.
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This option is deprecated.
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<br><dt><code>-mapcs</code><dd><a name="index-mapcs-1396"></a>This is a synonym for <samp><span class="option">-mapcs-frame</span></samp> and is deprecated.
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<br><dt><code>-mthumb-interwork</code><dd><a name="index-mthumb_002dinterwork-1397"></a>Generate code that supports calling between the ARM and Thumb
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instruction sets. Without this option, on pre-v5 architectures, the
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two instruction sets cannot be reliably used inside one program. The
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default is <samp><span class="option">-mno-thumb-interwork</span></samp>, since slightly larger code
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is generated when <samp><span class="option">-mthumb-interwork</span></samp> is specified. In AAPCS
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configurations this option is meaningless.
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<br><dt><code>-mno-sched-prolog</code><dd><a name="index-mno_002dsched_002dprolog-1398"></a>Prevent the reordering of instructions in the function prologue, or the
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merging of those instruction with the instructions in the function's
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body. This means that all functions start with a recognizable set
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of instructions (or in fact one of a choice from a small set of
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different function prologues), and this information can be used to
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locate the start of functions inside an executable piece of code. The
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default is <samp><span class="option">-msched-prolog</span></samp>.
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<br><dt><code>-mfloat-abi=</code><var>name</var><dd><a name="index-mfloat_002dabi-1399"></a>Specifies which floating-point ABI to use. Permissible values
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are: ‘<samp><span class="samp">soft</span></samp>’, ‘<samp><span class="samp">softfp</span></samp>’ and ‘<samp><span class="samp">hard</span></samp>’.
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<p>Specifying ‘<samp><span class="samp">soft</span></samp>’ causes GCC to generate output containing
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library calls for floating-point operations.
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‘<samp><span class="samp">softfp</span></samp>’ allows the generation of code using hardware floating-point
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instructions, but still uses the soft-float calling conventions.
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‘<samp><span class="samp">hard</span></samp>’ allows generation of floating-point instructions
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and uses FPU-specific calling conventions.
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<p>The default depends on the specific target configuration. Note that
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the hard-float and soft-float ABIs are not link-compatible; you must
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compile your entire program with the same ABI, and link with a
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compatible set of libraries.
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<br><dt><code>-mlittle-endian</code><dd><a name="index-mlittle_002dendian-1400"></a>Generate code for a processor running in little-endian mode. This is
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the default for all standard configurations.
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<br><dt><code>-mbig-endian</code><dd><a name="index-mbig_002dendian-1401"></a>Generate code for a processor running in big-endian mode; the default is
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to compile code for a little-endian processor.
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<br><dt><code>-march=</code><var>name</var><dd><a name="index-march-1402"></a>This specifies the name of the target ARM architecture. GCC uses this
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name to determine what kind of instructions it can emit when generating
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assembly code. This option can be used in conjunction with or instead
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of the <samp><span class="option">-mcpu=</span></samp> option. Permissible names are: ‘<samp><span class="samp">armv2</span></samp>’,
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‘<samp><span class="samp">armv2a</span></samp>’, ‘<samp><span class="samp">armv3</span></samp>’, ‘<samp><span class="samp">armv3m</span></samp>’, ‘<samp><span class="samp">armv4</span></samp>’, ‘<samp><span class="samp">armv4t</span></samp>’,
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‘<samp><span class="samp">armv5</span></samp>’, ‘<samp><span class="samp">armv5t</span></samp>’, ‘<samp><span class="samp">armv5e</span></samp>’, ‘<samp><span class="samp">armv5te</span></samp>’,
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‘<samp><span class="samp">armv6</span></samp>’, ‘<samp><span class="samp">armv6j</span></samp>’,
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‘<samp><span class="samp">armv6t2</span></samp>’, ‘<samp><span class="samp">armv6z</span></samp>’, ‘<samp><span class="samp">armv6zk</span></samp>’, ‘<samp><span class="samp">armv6-m</span></samp>’,
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‘<samp><span class="samp">armv7</span></samp>’, ‘<samp><span class="samp">armv7-a</span></samp>’, ‘<samp><span class="samp">armv7-r</span></samp>’, ‘<samp><span class="samp">armv7-m</span></samp>’, ‘<samp><span class="samp">armv7e-m</span></samp>’,
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‘<samp><span class="samp">armv7ve</span></samp>’, ‘<samp><span class="samp">armv8-a</span></samp>’, ‘<samp><span class="samp">armv8-a+crc</span></samp>’,
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‘<samp><span class="samp">iwmmxt</span></samp>’, ‘<samp><span class="samp">iwmmxt2</span></samp>’, ‘<samp><span class="samp">ep9312</span></samp>’.
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<p><samp><span class="option">-march=armv7ve</span></samp> is the armv7-a architecture with virtualization
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extensions.
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<p><samp><span class="option">-march=armv8-a+crc</span></samp> enables code generation for the ARMv8-A
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architecture together with the optional CRC32 extensions.
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<p><samp><span class="option">-march=native</span></samp> causes the compiler to auto-detect the architecture
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of the build computer. At present, this feature is only supported on
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GNU/Linux, and not all architectures are recognized. If the auto-detect
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is unsuccessful the option has no effect.
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<br><dt><code>-mtune=</code><var>name</var><dd><a name="index-mtune-1403"></a>This option specifies the name of the target ARM processor for
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which GCC should tune the performance of the code.
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For some ARM implementations better performance can be obtained by using
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this option.
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Permissible names are: ‘<samp><span class="samp">arm2</span></samp>’, ‘<samp><span class="samp">arm250</span></samp>’,
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‘<samp><span class="samp">arm3</span></samp>’, ‘<samp><span class="samp">arm6</span></samp>’, ‘<samp><span class="samp">arm60</span></samp>’, ‘<samp><span class="samp">arm600</span></samp>’, ‘<samp><span class="samp">arm610</span></samp>’,
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‘<samp><span class="samp">arm620</span></samp>’, ‘<samp><span class="samp">arm7</span></samp>’, ‘<samp><span class="samp">arm7m</span></samp>’, ‘<samp><span class="samp">arm7d</span></samp>’, ‘<samp><span class="samp">arm7dm</span></samp>’,
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‘<samp><span class="samp">arm7di</span></samp>’, ‘<samp><span class="samp">arm7dmi</span></samp>’, ‘<samp><span class="samp">arm70</span></samp>’, ‘<samp><span class="samp">arm700</span></samp>’,
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‘<samp><span class="samp">arm700i</span></samp>’, ‘<samp><span class="samp">arm710</span></samp>’, ‘<samp><span class="samp">arm710c</span></samp>’, ‘<samp><span class="samp">arm7100</span></samp>’,
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‘<samp><span class="samp">arm720</span></samp>’,
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‘<samp><span class="samp">arm7500</span></samp>’, ‘<samp><span class="samp">arm7500fe</span></samp>’, ‘<samp><span class="samp">arm7tdmi</span></samp>’, ‘<samp><span class="samp">arm7tdmi-s</span></samp>’,
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‘<samp><span class="samp">arm710t</span></samp>’, ‘<samp><span class="samp">arm720t</span></samp>’, ‘<samp><span class="samp">arm740t</span></samp>’,
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‘<samp><span class="samp">strongarm</span></samp>’, ‘<samp><span class="samp">strongarm110</span></samp>’, ‘<samp><span class="samp">strongarm1100</span></samp>’,
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‘<samp><span class="samp">strongarm1110</span></samp>’,
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‘<samp><span class="samp">arm8</span></samp>’, ‘<samp><span class="samp">arm810</span></samp>’, ‘<samp><span class="samp">arm9</span></samp>’, ‘<samp><span class="samp">arm9e</span></samp>’, ‘<samp><span class="samp">arm920</span></samp>’,
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‘<samp><span class="samp">arm920t</span></samp>’, ‘<samp><span class="samp">arm922t</span></samp>’, ‘<samp><span class="samp">arm946e-s</span></samp>’, ‘<samp><span class="samp">arm966e-s</span></samp>’,
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‘<samp><span class="samp">arm968e-s</span></samp>’, ‘<samp><span class="samp">arm926ej-s</span></samp>’, ‘<samp><span class="samp">arm940t</span></samp>’, ‘<samp><span class="samp">arm9tdmi</span></samp>’,
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‘<samp><span class="samp">arm10tdmi</span></samp>’, ‘<samp><span class="samp">arm1020t</span></samp>’, ‘<samp><span class="samp">arm1026ej-s</span></samp>’,
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‘<samp><span class="samp">arm10e</span></samp>’, ‘<samp><span class="samp">arm1020e</span></samp>’, ‘<samp><span class="samp">arm1022e</span></samp>’,
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‘<samp><span class="samp">arm1136j-s</span></samp>’, ‘<samp><span class="samp">arm1136jf-s</span></samp>’, ‘<samp><span class="samp">mpcore</span></samp>’, ‘<samp><span class="samp">mpcorenovfp</span></samp>’,
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‘<samp><span class="samp">arm1156t2-s</span></samp>’, ‘<samp><span class="samp">arm1156t2f-s</span></samp>’, ‘<samp><span class="samp">arm1176jz-s</span></samp>’, ‘<samp><span class="samp">arm1176jzf-s</span></samp>’,
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‘<samp><span class="samp">cortex-a5</span></samp>’, ‘<samp><span class="samp">cortex-a7</span></samp>’, ‘<samp><span class="samp">cortex-a8</span></samp>’, ‘<samp><span class="samp">cortex-a9</span></samp>’,
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‘<samp><span class="samp">cortex-a12</span></samp>’, ‘<samp><span class="samp">cortex-a15</span></samp>’, ‘<samp><span class="samp">cortex-a53</span></samp>’,
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‘<samp><span class="samp">cortex-a57</span></samp>’, ‘<samp><span class="samp">cortex-a72</span></samp>’,
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‘<samp><span class="samp">cortex-r4</span></samp>’,
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‘<samp><span class="samp">cortex-r4f</span></samp>’, ‘<samp><span class="samp">cortex-r5</span></samp>’, ‘<samp><span class="samp">cortex-r7</span></samp>’, ‘<samp><span class="samp">cortex-m7</span></samp>’,
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‘<samp><span class="samp">cortex-m4</span></samp>’,
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‘<samp><span class="samp">cortex-m3</span></samp>’,
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‘<samp><span class="samp">cortex-m1</span></samp>’,
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‘<samp><span class="samp">cortex-m0</span></samp>’,
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‘<samp><span class="samp">cortex-m0plus</span></samp>’,
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‘<samp><span class="samp">cortex-m1.small-multiply</span></samp>’,
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‘<samp><span class="samp">cortex-m0.small-multiply</span></samp>’,
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‘<samp><span class="samp">cortex-m0plus.small-multiply</span></samp>’,
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‘<samp><span class="samp">exynos-m1</span></samp>’,
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‘<samp><span class="samp">marvell-pj4</span></samp>’,
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‘<samp><span class="samp">xscale</span></samp>’, ‘<samp><span class="samp">iwmmxt</span></samp>’, ‘<samp><span class="samp">iwmmxt2</span></samp>’, ‘<samp><span class="samp">ep9312</span></samp>’,
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‘<samp><span class="samp">fa526</span></samp>’, ‘<samp><span class="samp">fa626</span></samp>’,
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‘<samp><span class="samp">fa606te</span></samp>’, ‘<samp><span class="samp">fa626te</span></samp>’, ‘<samp><span class="samp">fmp626</span></samp>’, ‘<samp><span class="samp">fa726te</span></samp>’,
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‘<samp><span class="samp">xgene1</span></samp>’.
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<p>Additionally, this option can specify that GCC should tune the performance
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of the code for a big.LITTLE system. Permissible names are:
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‘<samp><span class="samp">cortex-a15.cortex-a7</span></samp>’, ‘<samp><span class="samp">cortex-a57.cortex-a53</span></samp>’,
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‘<samp><span class="samp">cortex-a72.cortex-a53</span></samp>’.
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<p><samp><span class="option">-mtune=generic-</span><var>arch</var></samp> specifies that GCC should tune the
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performance for a blend of processors within architecture <var>arch</var>.
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The aim is to generate code that run well on the current most popular
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processors, balancing between optimizations that benefit some CPUs in the
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range, and avoiding performance pitfalls of other CPUs. The effects of
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this option may change in future GCC versions as CPU models come and go.
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<p><samp><span class="option">-mtune=native</span></samp> causes the compiler to auto-detect the CPU
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of the build computer. At present, this feature is only supported on
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GNU/Linux, and not all architectures are recognized. If the auto-detect is
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unsuccessful the option has no effect.
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<br><dt><code>-mcpu=</code><var>name</var><dd><a name="index-mcpu-1404"></a>This specifies the name of the target ARM processor. GCC uses this name
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to derive the name of the target ARM architecture (as if specified
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by <samp><span class="option">-march</span></samp>) and the ARM processor type for which to tune for
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performance (as if specified by <samp><span class="option">-mtune</span></samp>). Where this option
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is used in conjunction with <samp><span class="option">-march</span></samp> or <samp><span class="option">-mtune</span></samp>,
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those options take precedence over the appropriate part of this option.
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<p>Permissible names for this option are the same as those for
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<samp><span class="option">-mtune</span></samp>.
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<p><samp><span class="option">-mcpu=generic-</span><var>arch</var></samp> is also permissible, and is
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equivalent to <samp><span class="option">-march=</span><var>arch</var><span class="option"> -mtune=generic-</span><var>arch</var></samp>.
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See <samp><span class="option">-mtune</span></samp> for more information.
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<p><samp><span class="option">-mcpu=native</span></samp> causes the compiler to auto-detect the CPU
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of the build computer. At present, this feature is only supported on
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GNU/Linux, and not all architectures are recognized. If the auto-detect
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is unsuccessful the option has no effect.
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<br><dt><code>-mfpu=</code><var>name</var><dd><a name="index-mfpu-1405"></a>This specifies what floating-point hardware (or hardware emulation) is
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available on the target. Permissible names are: ‘<samp><span class="samp">vfp</span></samp>’, ‘<samp><span class="samp">vfpv3</span></samp>’,
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‘<samp><span class="samp">vfpv3-fp16</span></samp>’, ‘<samp><span class="samp">vfpv3-d16</span></samp>’, ‘<samp><span class="samp">vfpv3-d16-fp16</span></samp>’, ‘<samp><span class="samp">vfpv3xd</span></samp>’,
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‘<samp><span class="samp">vfpv3xd-fp16</span></samp>’, ‘<samp><span class="samp">neon</span></samp>’, ‘<samp><span class="samp">neon-fp16</span></samp>’, ‘<samp><span class="samp">vfpv4</span></samp>’,
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‘<samp><span class="samp">vfpv4-d16</span></samp>’, ‘<samp><span class="samp">fpv4-sp-d16</span></samp>’, ‘<samp><span class="samp">neon-vfpv4</span></samp>’,
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‘<samp><span class="samp">fpv5-d16</span></samp>’, ‘<samp><span class="samp">fpv5-sp-d16</span></samp>’,
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‘<samp><span class="samp">fp-armv8</span></samp>’, ‘<samp><span class="samp">neon-fp-armv8</span></samp>’, and ‘<samp><span class="samp">crypto-neon-fp-armv8</span></samp>’.
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<p>If <samp><span class="option">-msoft-float</span></samp> is specified this specifies the format of
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floating-point values.
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<p>If the selected floating-point hardware includes the NEON extension
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(e.g. <samp><span class="option">-mfpu</span></samp>=‘<samp><span class="samp">neon</span></samp>’), note that floating-point
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operations are not generated by GCC's auto-vectorization pass unless
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<samp><span class="option">-funsafe-math-optimizations</span></samp> is also specified. This is
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because NEON hardware does not fully implement the IEEE 754 standard for
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floating-point arithmetic (in particular denormal values are treated as
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zero), so the use of NEON instructions may lead to a loss of precision.
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<br><dt><code>-mfp16-format=</code><var>name</var><dd><a name="index-mfp16_002dformat-1406"></a>Specify the format of the <code>__fp16</code> half-precision floating-point type.
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Permissible names are ‘<samp><span class="samp">none</span></samp>’, ‘<samp><span class="samp">ieee</span></samp>’, and ‘<samp><span class="samp">alternative</span></samp>’;
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the default is ‘<samp><span class="samp">none</span></samp>’, in which case the <code>__fp16</code> type is not
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defined. See <a href="Half_002dPrecision.html#Half_002dPrecision">Half-Precision</a>, for more information.
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<br><dt><code>-mstructure-size-boundary=</code><var>n</var><dd><a name="index-mstructure_002dsize_002dboundary-1407"></a>The sizes of all structures and unions are rounded up to a multiple
|
|
of the number of bits set by this option. Permissible values are 8, 32
|
|
and 64. The default value varies for different toolchains. For the COFF
|
|
targeted toolchain the default value is 8. A value of 64 is only allowed
|
|
if the underlying ABI supports it.
|
|
|
|
<p>Specifying a larger number can produce faster, more efficient code, but
|
|
can also increase the size of the program. Different values are potentially
|
|
incompatible. Code compiled with one value cannot necessarily expect to
|
|
work with code or libraries compiled with another value, if they exchange
|
|
information using structures or unions.
|
|
|
|
<br><dt><code>-mabort-on-noreturn</code><dd><a name="index-mabort_002don_002dnoreturn-1408"></a>Generate a call to the function <code>abort</code> at the end of a
|
|
<code>noreturn</code> function. It is executed if the function tries to
|
|
return.
|
|
|
|
<br><dt><code>-mlong-calls</code><dt><code>-mno-long-calls</code><dd><a name="index-mlong_002dcalls-1409"></a><a name="index-mno_002dlong_002dcalls-1410"></a>Tells the compiler to perform function calls by first loading the
|
|
address of the function into a register and then performing a subroutine
|
|
call on this register. This switch is needed if the target function
|
|
lies outside of the 64-megabyte addressing range of the offset-based
|
|
version of subroutine call instruction.
|
|
|
|
<p>Even if this switch is enabled, not all function calls are turned
|
|
into long calls. The heuristic is that static functions, functions
|
|
that have the <code>short_call</code> attribute, functions that are inside
|
|
the scope of a <code>#pragma no_long_calls</code> directive, and functions whose
|
|
definitions have already been compiled within the current compilation
|
|
unit are not turned into long calls. The exceptions to this rule are
|
|
that weak function definitions, functions with the <code>long_call</code>
|
|
attribute or the <code>section</code> attribute, and functions that are within
|
|
the scope of a <code>#pragma long_calls</code> directive are always
|
|
turned into long calls.
|
|
|
|
<p>This feature is not enabled by default. Specifying
|
|
<samp><span class="option">-mno-long-calls</span></samp> restores the default behavior, as does
|
|
placing the function calls within the scope of a <code>#pragma
|
|
long_calls_off</code> directive. Note these switches have no effect on how
|
|
the compiler generates code to handle function calls via function
|
|
pointers.
|
|
|
|
<br><dt><code>-msingle-pic-base</code><dd><a name="index-msingle_002dpic_002dbase-1411"></a>Treat the register used for PIC addressing as read-only, rather than
|
|
loading it in the prologue for each function. The runtime system is
|
|
responsible for initializing this register with an appropriate value
|
|
before execution begins.
|
|
|
|
<br><dt><code>-mpic-register=</code><var>reg</var><dd><a name="index-mpic_002dregister-1412"></a>Specify the register to be used for PIC addressing.
|
|
For standard PIC base case, the default is any suitable register
|
|
determined by compiler. For single PIC base case, the default is
|
|
‘<samp><span class="samp">R9</span></samp>’ if target is EABI based or stack-checking is enabled,
|
|
otherwise the default is ‘<samp><span class="samp">R10</span></samp>’.
|
|
|
|
<br><dt><code>-mpic-data-is-text-relative</code><dd><a name="index-mpic_002ddata_002dis_002dtext_002drelative-1413"></a>Assume that each data segments are relative to text segment at load time.
|
|
Therefore, it permits addressing data using PC-relative operations.
|
|
This option is on by default for targets other than VxWorks RTP.
|
|
|
|
<br><dt><code>-mpoke-function-name</code><dd><a name="index-mpoke_002dfunction_002dname-1414"></a>Write the name of each function into the text section, directly
|
|
preceding the function prologue. The generated code is similar to this:
|
|
|
|
<pre class="smallexample"> t0
|
|
.ascii "arm_poke_function_name", 0
|
|
.align
|
|
t1
|
|
.word 0xff000000 + (t1 - t0)
|
|
arm_poke_function_name
|
|
mov ip, sp
|
|
stmfd sp!, {fp, ip, lr, pc}
|
|
sub fp, ip, #4
|
|
</pre>
|
|
<p>When performing a stack backtrace, code can inspect the value of
|
|
<code>pc</code> stored at <code>fp + 0</code>. If the trace function then looks at
|
|
location <code>pc - 12</code> and the top 8 bits are set, then we know that
|
|
there is a function name embedded immediately preceding this location
|
|
and has length <code>((pc[-3]) & 0xff000000)</code>.
|
|
|
|
<br><dt><code>-mthumb</code><dt><code>-marm</code><dd><a name="index-marm-1415"></a><a name="index-mthumb-1416"></a>
|
|
Select between generating code that executes in ARM and Thumb
|
|
states. The default for most configurations is to generate code
|
|
that executes in ARM state, but the default can be changed by
|
|
configuring GCC with the <samp><span class="option">--with-mode=</span></samp><var>state</var>
|
|
configure option.
|
|
|
|
<br><dt><code>-mtpcs-frame</code><dd><a name="index-mtpcs_002dframe-1417"></a>Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all non-leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is <samp><span class="option">-mno-tpcs-frame</span></samp>.
|
|
|
|
<br><dt><code>-mtpcs-leaf-frame</code><dd><a name="index-mtpcs_002dleaf_002dframe-1418"></a>Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is <samp><span class="option">-mno-apcs-leaf-frame</span></samp>.
|
|
|
|
<br><dt><code>-mcallee-super-interworking</code><dd><a name="index-mcallee_002dsuper_002dinterworking-1419"></a>Gives all externally visible functions in the file being compiled an ARM
|
|
instruction set header which switches to Thumb mode before executing the
|
|
rest of the function. This allows these functions to be called from
|
|
non-interworking code. This option is not valid in AAPCS configurations
|
|
because interworking is enabled by default.
|
|
|
|
<br><dt><code>-mcaller-super-interworking</code><dd><a name="index-mcaller_002dsuper_002dinterworking-1420"></a>Allows calls via function pointers (including virtual functions) to
|
|
execute correctly regardless of whether the target code has been
|
|
compiled for interworking or not. There is a small overhead in the cost
|
|
of executing a function pointer if this option is enabled. This option
|
|
is not valid in AAPCS configurations because interworking is enabled
|
|
by default.
|
|
|
|
<br><dt><code>-mtp=</code><var>name</var><dd><a name="index-mtp-1421"></a>Specify the access model for the thread local storage pointer. The valid
|
|
models are ‘<samp><span class="samp">soft</span></samp>’, which generates calls to <code>__aeabi_read_tp</code>,
|
|
‘<samp><span class="samp">cp15</span></samp>’, which fetches the thread pointer from <code>cp15</code> directly
|
|
(supported in the arm6k architecture), and ‘<samp><span class="samp">auto</span></samp>’, which uses the
|
|
best available method for the selected processor. The default setting is
|
|
‘<samp><span class="samp">auto</span></samp>’.
|
|
|
|
<br><dt><code>-mtls-dialect=</code><var>dialect</var><dd><a name="index-mtls_002ddialect-1422"></a>Specify the dialect to use for accessing thread local storage. Two
|
|
<var>dialect</var>s are supported—‘<samp><span class="samp">gnu</span></samp>’ and ‘<samp><span class="samp">gnu2</span></samp>’. The
|
|
‘<samp><span class="samp">gnu</span></samp>’ dialect selects the original GNU scheme for supporting
|
|
local and global dynamic TLS models. The ‘<samp><span class="samp">gnu2</span></samp>’ dialect
|
|
selects the GNU descriptor scheme, which provides better performance
|
|
for shared libraries. The GNU descriptor scheme is compatible with
|
|
the original scheme, but does require new assembler, linker and
|
|
library support. Initial and local exec TLS models are unaffected by
|
|
this option and always use the original scheme.
|
|
|
|
<br><dt><code>-mword-relocations</code><dd><a name="index-mword_002drelocations-1423"></a>Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32).
|
|
This is enabled by default on targets (uClinux, SymbianOS) where the runtime
|
|
loader imposes this restriction, and when <samp><span class="option">-fpic</span></samp> or <samp><span class="option">-fPIC</span></samp>
|
|
is specified.
|
|
|
|
<br><dt><code>-mfix-cortex-m3-ldrd</code><dd><a name="index-mfix_002dcortex_002dm3_002dldrd-1424"></a>Some Cortex-M3 cores can cause data corruption when <code>ldrd</code> instructions
|
|
with overlapping destination and base registers are used. This option avoids
|
|
generating these instructions. This option is enabled by default when
|
|
<samp><span class="option">-mcpu=cortex-m3</span></samp> is specified.
|
|
|
|
<br><dt><code>-munaligned-access</code><dt><code>-mno-unaligned-access</code><dd><a name="index-munaligned_002daccess-1425"></a><a name="index-mno_002dunaligned_002daccess-1426"></a>Enables (or disables) reading and writing of 16- and 32- bit values
|
|
from addresses that are not 16- or 32- bit aligned. By default
|
|
unaligned access is disabled for all pre-ARMv6 and all ARMv6-M
|
|
architectures, and enabled for all other architectures. If unaligned
|
|
access is not enabled then words in packed data structures are
|
|
accessed a byte at a time.
|
|
|
|
<p>The ARM attribute <code>Tag_CPU_unaligned_access</code> is set in the
|
|
generated object file to either true or false, depending upon the
|
|
setting of this option. If unaligned access is enabled then the
|
|
preprocessor symbol <code>__ARM_FEATURE_UNALIGNED</code> is also
|
|
defined.
|
|
|
|
<br><dt><code>-mneon-for-64bits</code><dd><a name="index-mneon_002dfor_002d64bits-1427"></a>Enables using Neon to handle scalar 64-bits operations. This is
|
|
disabled by default since the cost of moving data from core registers
|
|
to Neon is high.
|
|
|
|
<br><dt><code>-mslow-flash-data</code><dd><a name="index-mslow_002dflash_002ddata-1428"></a>Assume loading data from flash is slower than fetching instruction.
|
|
Therefore literal load is minimized for better performance.
|
|
This option is only supported when compiling for ARMv7 M-profile and
|
|
off by default.
|
|
|
|
<br><dt><code>-masm-syntax-unified</code><dd><a name="index-masm_002dsyntax_002dunified-1429"></a>Assume inline assembler is using unified asm syntax. The default is
|
|
currently off which implies divided syntax. Currently this option is
|
|
available only for Thumb1 and has no effect on ARM state and Thumb2.
|
|
However, this may change in future releases of GCC. Divided syntax
|
|
should be considered deprecated.
|
|
|
|
<br><dt><code>-mrestrict-it</code><dd><a name="index-mrestrict_002dit-1430"></a>Restricts generation of IT blocks to conform to the rules of ARMv8.
|
|
IT blocks can only contain a single 16-bit instruction from a select
|
|
set of instructions. This option is on by default for ARMv8 Thumb mode.
|
|
|
|
<br><dt><code>-mprint-tune-info</code><dd><a name="index-mprint_002dtune_002dinfo-1431"></a>Print CPU tuning information as comment in assembler file. This is
|
|
an option used only for regression testing of the compiler and not
|
|
intended for ordinary use in compiling code. This option is disabled
|
|
by default.
|
|
</dl>
|
|
|
|
</body></html>
|
|
|