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| Next: <a href="Symbol_002dtable.html#Symbol_002dtable" accesskey="n" rel="next">Symbol-table</a>, Previous: <a href="mmo.html#mmo" accesskey="p" rel="prev">mmo</a>, Up: <a href="mmo.html#mmo" accesskey="u" rel="up">mmo</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="File-layout-2"></a> |
| <h4 class="subsection">3.5.1 File layout</h4> |
| <p>The mmo file contents is not partitioned into named sections as |
| with e.g. ELF. Memory areas is formed by specifying the |
| location of the data that follows. Only the memory area |
| ‘<samp>0x0000…00</samp>’ to ‘<samp>0x01ff…ff</samp>’ is executable, so |
| it is used for code (and constants) and the area |
| ‘<samp>0x2000…00</samp>’ to ‘<samp>0x20ff…ff</samp>’ is used for |
| writable data. See <a href="mmo-section-mapping.html#mmo-section-mapping">mmo section mapping</a>. |
| </p> |
| <p>There is provision for specifying “special data” of 65536 |
| different types. We use type 80 (decimal), arbitrarily chosen the |
| same as the ELF <code>e_machine</code> number for MMIX, filling it with |
| section information normally found in ELF objects. See <a href="mmo-section-mapping.html#mmo-section-mapping">mmo section mapping</a>. |
| </p> |
| <p>Contents is entered as 32-bit words, xor:ed over previous |
| contents, always zero-initialized. A word that starts with the |
| byte ‘<samp>0x98</samp>’ forms a command called a ‘<samp>lopcode</samp>’, where |
| the next byte distinguished between the thirteen lopcodes. The |
| two remaining bytes, called the ‘<samp>Y</samp>’ and ‘<samp>Z</samp>’ fields, or |
| the ‘<samp>YZ</samp>’ field (a 16-bit big-endian number), are used for |
| various purposes different for each lopcode. As documented in |
| <a href="http://www-cs-faculty.stanford.edu/~knuth/mmixal-intro.ps.gz">http://www-cs-faculty.stanford.edu/~knuth/mmixal-intro.ps.gz</a>, |
| the lopcodes are: |
| </p> |
| <dl compact="compact"> |
| <dt><code>lop_quote</code></dt> |
| <dd><p>0x98000001. The next word is contents, regardless of whether it |
| starts with 0x98 or not. |
| </p> |
| </dd> |
| <dt><code>lop_loc</code></dt> |
| <dd><p>0x9801YYZZ, where ‘<samp>Z</samp>’ is 1 or 2. This is a location |
| directive, setting the location for the next data to the next |
| 32-bit word (for <em>Z = 1</em>) or 64-bit word (for <em>Z = 2</em>), |
| plus <em>Y * 2^56</em>. Normally ‘<samp>Y</samp>’ is 0 for the text segment |
| and 2 for the data segment. |
| </p> |
| </dd> |
| <dt><code>lop_skip</code></dt> |
| <dd><p>0x9802YYZZ. Increase the current location by ‘<samp>YZ</samp>’ bytes. |
| </p> |
| </dd> |
| <dt><code>lop_fixo</code></dt> |
| <dd><p>0x9803YYZZ, where ‘<samp>Z</samp>’ is 1 or 2. Store the current location |
| as 64 bits into the location pointed to by the next 32-bit |
| (<em>Z = 1</em>) or 64-bit (<em>Z = 2</em>) word, plus <em>Y * |
| 2^56</em>. |
| </p> |
| </dd> |
| <dt><code>lop_fixr</code></dt> |
| <dd><p>0x9804YYZZ. ‘<samp>YZ</samp>’ is stored into the current location plus |
| <em>2 - 4 * YZ</em>. |
| </p> |
| </dd> |
| <dt><code>lop_fixrx</code></dt> |
| <dd><p>0x980500ZZ. ‘<samp>Z</samp>’ is 16 or 24. A value ‘<samp>L</samp>’ derived from |
| the following 32-bit word are used in a manner similar to |
| ‘<samp>YZ</samp>’ in lop_fixr: it is xor:ed into the current location |
| minus <em>4 * L</em>. The first byte of the word is 0 or 1. If it |
| is 1, then <em>L = (<var>lowest 24 bits of word</var>) - 2^Z</em>, if 0, |
| then <em>L = (<var>lowest 24 bits of word</var>)</em>. |
| </p> |
| </dd> |
| <dt><code>lop_file</code></dt> |
| <dd><p>0x9806YYZZ. ‘<samp>Y</samp>’ is the file number, ‘<samp>Z</samp>’ is count of |
| 32-bit words. Set the file number to ‘<samp>Y</samp>’ and the line |
| counter to 0. The next <em>Z * 4</em> bytes contain the file name, |
| padded with zeros if the count is not a multiple of four. The |
| same ‘<samp>Y</samp>’ may occur multiple times, but ‘<samp>Z</samp>’ must be 0 for |
| all but the first occurrence. |
| </p> |
| </dd> |
| <dt><code>lop_line</code></dt> |
| <dd><p>0x9807YYZZ. ‘<samp>YZ</samp>’ is the line number. Together with |
| lop_file, it forms the source location for the next 32-bit word. |
| Note that for each non-lopcode 32-bit word, line numbers are |
| assumed incremented by one. |
| </p> |
| </dd> |
| <dt><code>lop_spec</code></dt> |
| <dd><p>0x9808YYZZ. ‘<samp>YZ</samp>’ is the type number. Data until the next |
| lopcode other than lop_quote forms special data of type ‘<samp>YZ</samp>’. |
| See <a href="mmo-section-mapping.html#mmo-section-mapping">mmo section mapping</a>. |
| </p> |
| <p>Other types than 80, (or type 80 with a content that does not |
| parse) is stored in sections named <code>.MMIX.spec_data.<var>n</var></code> |
| where <var>n</var> is the ‘<samp>YZ</samp>’-type. The flags for such a |
| sections say not to allocate or load the data. The vma is 0. |
| Contents of multiple occurrences of special data <var>n</var> is |
| concatenated to the data of the previous lop_spec <var>n</var>s. The |
| location in data or code at which the lop_spec occurred is lost. |
| </p> |
| </dd> |
| <dt><code>lop_pre</code></dt> |
| <dd><p>0x980901ZZ. The first lopcode in a file. The ‘<samp>Z</samp>’ field forms the |
| length of header information in 32-bit words, where the first word |
| tells the time in seconds since ‘<samp>00:00:00 GMT Jan 1 1970</samp>’. |
| </p> |
| </dd> |
| <dt><code>lop_post</code></dt> |
| <dd><p>0x980a00ZZ. <em>Z > 32</em>. This lopcode follows after all |
| content-generating lopcodes in a program. The ‘<samp>Z</samp>’ field |
| denotes the value of ‘<samp>rG</samp>’ at the beginning of the program. |
| The following <em>256 - Z</em> big-endian 64-bit words are loaded |
| into global registers ‘<samp>$G</samp>’ … ‘<samp>$255</samp>’. |
| </p> |
| </dd> |
| <dt><code>lop_stab</code></dt> |
| <dd><p>0x980b0000. The next-to-last lopcode in a program. Must follow |
| immediately after the lop_post lopcode and its data. After this |
| lopcode follows all symbols in a compressed format |
| (see <a href="Symbol_002dtable.html#Symbol_002dtable">Symbol-table</a>). |
| </p> |
| </dd> |
| <dt><code>lop_end</code></dt> |
| <dd><p>0x980cYYZZ. The last lopcode in a program. It must follow the |
| lop_stab lopcode and its data. The ‘<samp>YZ</samp>’ field contains the |
| number of 32-bit words of symbol table information after the |
| preceding lop_stab lopcode. |
| </p></dd> |
| </dl> |
| |
| <p>Note that the lopcode "fixups"; <code>lop_fixr</code>, <code>lop_fixrx</code> and |
| <code>lop_fixo</code> are not generated by BFD, but are handled. They are |
| generated by <code>mmixal</code>. |
| </p> |
| <p>This trivial one-label, one-instruction file: |
| </p> |
| <div class="example"> |
| <pre class="example"> :Main TRAP 1,2,3 |
| </pre></div> |
| |
| <p>can be represented this way in mmo: |
| </p> |
| <div class="example"> |
| <pre class="example"> 0x98090101 - lop_pre, one 32-bit word with timestamp. |
| <timestamp> |
| 0x98010002 - lop_loc, text segment, using a 64-bit address. |
| Note that mmixal does not emit this for the file above. |
| 0x00000000 - Address, high 32 bits. |
| 0x00000000 - Address, low 32 bits. |
| 0x98060002 - lop_file, 2 32-bit words for file-name. |
| 0x74657374 - "test" |
| 0x2e730000 - ".s\0\0" |
| 0x98070001 - lop_line, line 1. |
| 0x00010203 - TRAP 1,2,3 |
| 0x980a00ff - lop_post, setting $255 to 0. |
| 0x00000000 |
| 0x00000000 |
| 0x980b0000 - lop_stab for ":Main" = 0, serial 1. |
| 0x203a4040 See <a href="Symbol_002dtable.html#Symbol_002dtable">Symbol-table</a>. |
| 0x10404020 |
| 0x4d206120 |
| 0x69016e00 |
| 0x81000000 |
| 0x980c0005 - lop_end; symbol table contained five 32-bit words. |
| </pre></div> |
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