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| Previous: <a href="Symbol_002dtable.html#Symbol_002dtable" accesskey="p" rel="prev">Symbol-table</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="mmo-section-mapping-1"></a> |
| <h4 class="subsection">3.5.3 mmo section mapping</h4> |
| <p>The implementation in BFD uses special data type 80 (decimal) to |
| encapsulate and describe named sections, containing e.g. debug |
| information. If needed, any datum in the encapsulation will be |
| quoted using lop_quote. First comes a 32-bit word holding the |
| number of 32-bit words containing the zero-terminated zero-padded |
| segment name. After the name there’s a 32-bit word holding flags |
| describing the section type. Then comes a 64-bit big-endian word |
| with the section length (in bytes), then another with the section |
| start address. Depending on the type of section, the contents |
| might follow, zero-padded to 32-bit boundary. For a loadable |
| section (such as data or code), the contents might follow at some |
| later point, not necessarily immediately, as a lop_loc with the |
| same start address as in the section description, followed by the |
| contents. This in effect forms a descriptor that must be emitted |
| before the actual contents. Sections described this way must not |
| overlap. |
| </p> |
| <p>For areas that don’t have such descriptors, synthetic sections are |
| formed by BFD. Consecutive contents in the two memory areas |
| ‘<samp>0x0000…00</samp>’ to ‘<samp>0x01ff…ff</samp>’ and |
| ‘<samp>0x2000…00</samp>’ to ‘<samp>0x20ff…ff</samp>’ are entered in |
| sections named <code>.text</code> and <code>.data</code> respectively. If an area |
| is not otherwise described, but would together with a neighboring |
| lower area be less than ‘<samp>0x40000000</samp>’ bytes long, it is joined |
| with the lower area and the gap is zero-filled. For other cases, |
| a new section is formed, named <code>.MMIX.sec.<var>n</var></code>. Here, |
| <var>n</var> is a number, a running count through the mmo file, |
| starting at 0. |
| </p> |
| <p>A loadable section specified as: |
| </p> |
| <div class="example"> |
| <pre class="example"> .section secname,"ax" |
| TETRA 1,2,3,4,-1,-2009 |
| BYTE 80 |
| </pre></div> |
| |
| <p>and linked to address ‘<samp>0x4</samp>’, is represented by the sequence: |
| </p> |
| <div class="example"> |
| <pre class="example"> 0x98080050 - lop_spec 80 |
| 0x00000002 - two 32-bit words for the section name |
| 0x7365636e - "secn" |
| 0x616d6500 - "ame\0" |
| 0x00000033 - flags CODE, READONLY, LOAD, ALLOC |
| 0x00000000 - high 32 bits of section length |
| 0x0000001c - section length is 28 bytes; 6 * 4 + 1 + alignment to 32 bits |
| 0x00000000 - high 32 bits of section address |
| 0x00000004 - section address is 4 |
| 0x98010002 - 64 bits with address of following data |
| 0x00000000 - high 32 bits of address |
| 0x00000004 - low 32 bits: data starts at address 4 |
| 0x00000001 - 1 |
| 0x00000002 - 2 |
| 0x00000003 - 3 |
| 0x00000004 - 4 |
| 0xffffffff - -1 |
| 0xfffff827 - -2009 |
| 0x50000000 - 80 as a byte, padded with zeros. |
| </pre></div> |
| |
| <p>Note that the lop_spec wrapping does not include the section |
| contents. Compare this to a non-loaded section specified as: |
| </p> |
| <div class="example"> |
| <pre class="example"> .section thirdsec |
| TETRA 200001,100002 |
| BYTE 38,40 |
| </pre></div> |
| |
| <p>This, when linked to address ‘<samp>0x200000000000001c</samp>’, is |
| represented by: |
| </p> |
| <div class="example"> |
| <pre class="example"> 0x98080050 - lop_spec 80 |
| 0x00000002 - two 32-bit words for the section name |
| 0x7365636e - "thir" |
| 0x616d6500 - "dsec" |
| 0x00000010 - flag READONLY |
| 0x00000000 - high 32 bits of section length |
| 0x0000000c - section length is 12 bytes; 2 * 4 + 2 + alignment to 32 bits |
| 0x20000000 - high 32 bits of address |
| 0x0000001c - low 32 bits of address 0x200000000000001c |
| 0x00030d41 - 200001 |
| 0x000186a2 - 100002 |
| 0x26280000 - 38, 40 as bytes, padded with zeros |
| </pre></div> |
| |
| <p>For the latter example, the section contents must not be |
| loaded in memory, and is therefore specified as part of the |
| special data. The address is usually unimportant but might |
| provide information for e.g. the DWARF 2 debugging format. |
| </p> |
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