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| <title>Using the GNU Compiler Collection (GCC): PowerPC Hardware Transactional Memory Built-in Functions</title> |
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| Next: <a href="RX-Built_002din-Functions.html#RX-Built_002din-Functions" accesskey="n" rel="next">RX Built-in Functions</a>, Previous: <a href="PowerPC-AltiVec_002fVSX-Built_002din-Functions.html#PowerPC-AltiVec_002fVSX-Built_002din-Functions" accesskey="p" rel="prev">PowerPC AltiVec/VSX Built-in Functions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <hr> |
| <a name="PowerPC-Hardware-Transactional-Memory-Built_002din-Functions-1"></a> |
| <h4 class="subsection">6.58.21 PowerPC Hardware Transactional Memory Built-in Functions</h4> |
| <p>GCC provides two interfaces for accessing the Hardware Transactional |
| Memory (HTM) instructions available on some of the PowerPC family |
| of processors (eg, POWER8). The two interfaces come in a low level |
| interface, consisting of built-in functions specific to PowerPC and a |
| higher level interface consisting of inline functions that are common |
| between PowerPC and S/390. |
| </p> |
| <a name="PowerPC-HTM-Low-Level-Built_002din-Functions"></a> |
| <h4 class="subsubsection">6.58.21.1 PowerPC HTM Low Level Built-in Functions</h4> |
| |
| <p>The following low level built-in functions are available with |
| <samp>-mhtm</samp> or <samp>-mcpu=CPU</samp> where CPU is ‘power8’ or later. |
| They all generate the machine instruction that is part of the name. |
| </p> |
| <p>The HTM builtins (with the exception of <code>__builtin_tbegin</code>) return |
| the full 4-bit condition register value set by their associated hardware |
| instruction. The header file <code>htmintrin.h</code> defines some macros that can |
| be used to decipher the return value. The <code>__builtin_tbegin</code> builtin |
| returns a simple true or false value depending on whether a transaction was |
| successfully started or not. The arguments of the builtins match exactly the |
| type and order of the associated hardware instruction’s operands, except for |
| the <code>__builtin_tcheck</code> builtin, which does not take any input arguments. |
| Refer to the ISA manual for a description of each instruction’s operands. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">unsigned int __builtin_tbegin (unsigned int) |
| unsigned int __builtin_tend (unsigned int) |
| |
| unsigned int __builtin_tabort (unsigned int) |
| unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int) |
| unsigned int __builtin_tabortdci (unsigned int, unsigned int, int) |
| unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int) |
| unsigned int __builtin_tabortwci (unsigned int, unsigned int, int) |
| |
| unsigned int __builtin_tcheck (void) |
| unsigned int __builtin_treclaim (unsigned int) |
| unsigned int __builtin_trechkpt (void) |
| unsigned int __builtin_tsr (unsigned int) |
| </pre></div> |
| |
| <p>In addition to the above HTM built-ins, we have added built-ins for |
| some common extended mnemonics of the HTM instructions: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">unsigned int __builtin_tendall (void) |
| unsigned int __builtin_tresume (void) |
| unsigned int __builtin_tsuspend (void) |
| </pre></div> |
| |
| <p>The following set of built-in functions are available to gain access |
| to the HTM specific special purpose registers. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">unsigned long __builtin_get_texasr (void) |
| unsigned long __builtin_get_texasru (void) |
| unsigned long __builtin_get_tfhar (void) |
| unsigned long __builtin_get_tfiar (void) |
| |
| void __builtin_set_texasr (unsigned long); |
| void __builtin_set_texasru (unsigned long); |
| void __builtin_set_tfhar (unsigned long); |
| void __builtin_set_tfiar (unsigned long); |
| </pre></div> |
| |
| <p>Example usage of these low level built-in functions may look like: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">#include <htmintrin.h> |
| |
| int num_retries = 10; |
| |
| while (1) |
| { |
| if (__builtin_tbegin (0)) |
| { |
| /* Transaction State Initiated. */ |
| if (is_locked (lock)) |
| __builtin_tabort (0); |
| ... transaction code... |
| __builtin_tend (0); |
| break; |
| } |
| else |
| { |
| /* Transaction State Failed. Use locks if the transaction |
| failure is "persistent" or we've tried too many times. */ |
| if (num_retries-- <= 0 |
| || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ())) |
| { |
| acquire_lock (lock); |
| ... non transactional fallback path... |
| release_lock (lock); |
| break; |
| } |
| } |
| } |
| </pre></div> |
| |
| <p>One final built-in function has been added that returns the value of |
| the 2-bit Transaction State field of the Machine Status Register (MSR) |
| as stored in <code>CR0</code>. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">unsigned long __builtin_ttest (void) |
| </pre></div> |
| |
| <p>This built-in can be used to determine the current transaction state |
| using the following code example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">#include <htmintrin.h> |
| |
| unsigned char tx_state = _HTM_STATE (__builtin_ttest ()); |
| |
| if (tx_state == _HTM_TRANSACTIONAL) |
| { |
| /* Code to use in transactional state. */ |
| } |
| else if (tx_state == _HTM_NONTRANSACTIONAL) |
| { |
| /* Code to use in non-transactional state. */ |
| } |
| else if (tx_state == _HTM_SUSPENDED) |
| { |
| /* Code to use in transaction suspended state. */ |
| } |
| </pre></div> |
| |
| <a name="PowerPC-HTM-High-Level-Inline-Functions"></a> |
| <h4 class="subsubsection">6.58.21.2 PowerPC HTM High Level Inline Functions</h4> |
| |
| <p>The following high level HTM interface is made available by including |
| <code><htmxlintrin.h></code> and using <samp>-mhtm</samp> or <samp>-mcpu=CPU</samp> |
| where CPU is ‘power8’ or later. This interface is common between PowerPC |
| and S/390, allowing users to write one HTM source implementation that |
| can be compiled and executed on either system. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">long __TM_simple_begin (void) |
| long __TM_begin (void* const TM_buff) |
| long __TM_end (void) |
| void __TM_abort (void) |
| void __TM_named_abort (unsigned char const code) |
| void __TM_resume (void) |
| void __TM_suspend (void) |
| |
| long __TM_is_user_abort (void* const TM_buff) |
| long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code) |
| long __TM_is_illegal (void* const TM_buff) |
| long __TM_is_footprint_exceeded (void* const TM_buff) |
| long __TM_nesting_depth (void* const TM_buff) |
| long __TM_is_nested_too_deep(void* const TM_buff) |
| long __TM_is_conflict(void* const TM_buff) |
| long __TM_is_failure_persistent(void* const TM_buff) |
| long __TM_failure_address(void* const TM_buff) |
| long long __TM_failure_code(void* const TM_buff) |
| </pre></div> |
| |
| <p>Using these common set of HTM inline functions, we can create |
| a more portable version of the HTM example in the previous |
| section that will work on either PowerPC or S/390: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">#include <htmxlintrin.h> |
| |
| int num_retries = 10; |
| TM_buff_type TM_buff; |
| |
| while (1) |
| { |
| if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED) |
| { |
| /* Transaction State Initiated. */ |
| if (is_locked (lock)) |
| __TM_abort (); |
| ... transaction code... |
| __TM_end (); |
| break; |
| } |
| else |
| { |
| /* Transaction State Failed. Use locks if the transaction |
| failure is "persistent" or we've tried too many times. */ |
| if (num_retries-- <= 0 |
| || __TM_is_failure_persistent (TM_buff)) |
| { |
| acquire_lock (lock); |
| ... non transactional fallback path... |
| release_lock (lock); |
| break; |
| } |
| } |
| } |
| </pre></div> |
| |
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| Next: <a href="RX-Built_002din-Functions.html#RX-Built_002din-Functions" accesskey="n" rel="next">RX Built-in Functions</a>, Previous: <a href="PowerPC-AltiVec_002fVSX-Built_002din-Functions.html#PowerPC-AltiVec_002fVSX-Built_002din-Functions" accesskey="p" rel="prev">PowerPC AltiVec/VSX Built-in Functions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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