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179 lines
8 KiB
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<html lang="en">
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<head>
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<title>CFI directives - Using as</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using as">
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<meta name="generator" content="makeinfo 4.7">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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<link rel="prev" href="Comm.html#Comm" title="Comm">
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<link rel="next" href="Data.html#Data" title="Data">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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man end-->
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span.roman { font-family: serif; font-weight: normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<p>
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<a name="CFI-directives"></a>Next: <a rel="next" accesskey="n" href="Data.html#Data">Data</a>,
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Previous: <a rel="previous" accesskey="p" href="Comm.html#Comm">Comm</a>,
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Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
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<hr><br>
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</div>
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<h3 class="section">7.9 <code>.cfi_startproc [simple]</code></h3>
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<p><a name="index-_0040code_007bcfi_005fstartproc_007d-directive-290"></a><code>.cfi_startproc</code> is used at the beginning of each function that
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should have an entry in <code>.eh_frame</code>. It initializes some internal
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data structures. Don't forget to close the function by
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<code>.cfi_endproc</code>.
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<p>Unless <code>.cfi_startproc</code> is used along with parameter <code>simple</code>
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it also emits some architecture dependent initial CFI instructions.
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<h3 class="section">7.10 <code>.cfi_endproc</code></h3>
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<p><a name="index-_0040code_007bcfi_005fendproc_007d-directive-291"></a><code>.cfi_endproc</code> is used at the end of a function where it closes its
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unwind entry previously opened by
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<code>.cfi_startproc</code>, and emits it to <code>.eh_frame</code>.
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<h3 class="section">7.11 <code>.cfi_personality </code><var>encoding</var><code> [, </code><var>exp</var><code>]</code></h3>
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<p><code>.cfi_personality</code> defines personality routine and its encoding.
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<var>encoding</var> must be a constant determining how the personality
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should be encoded. If it is 255 (<code>DW_EH_PE_omit</code>), second
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argument is not present, otherwise second argument should be
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a constant or a symbol name. When using indirect encodings,
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the symbol provided should be the location where personality
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can be loaded from, not the personality routine itself.
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The default after <code>.cfi_startproc</code> is <code>.cfi_personality 0xff</code>,
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no personality routine.
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<h3 class="section">7.12 <code>.cfi_lsda </code><var>encoding</var><code> [, </code><var>exp</var><code>]</code></h3>
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<p><code>.cfi_lsda</code> defines LSDA and its encoding.
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<var>encoding</var> must be a constant determining how the LSDA
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should be encoded. If it is 255 (<code>DW_EH_PE_omit</code>), second
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argument is not present, otherwise second argument should be a constant
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or a symbol name. The default after <code>.cfi_startproc</code> is <code>.cfi_lsda 0xff</code>,
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no LSDA.
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<h3 class="section">7.13 <code>.cfi_def_cfa </code><var>register</var><code>, </code><var>offset</var></h3>
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<p><code>.cfi_def_cfa</code> defines a rule for computing CFA as: <i>take
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address from </i><var>register</var><i> and add </i><var>offset</var><i> to it</i>.
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<h3 class="section">7.14 <code>.cfi_def_cfa_register </code><var>register</var></h3>
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<p><code>.cfi_def_cfa_register</code> modifies a rule for computing CFA. From
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now on <var>register</var> will be used instead of the old one. Offset
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remains the same.
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<h3 class="section">7.15 <code>.cfi_def_cfa_offset </code><var>offset</var></h3>
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<p><code>.cfi_def_cfa_offset</code> modifies a rule for computing CFA. Register
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remains the same, but <var>offset</var> is new. Note that it is the
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absolute offset that will be added to a defined register to compute
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CFA address.
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<h3 class="section">7.16 <code>.cfi_adjust_cfa_offset </code><var>offset</var></h3>
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<p>Same as <code>.cfi_def_cfa_offset</code> but <var>offset</var> is a relative
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value that is added/substracted from the previous offset.
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<h3 class="section">7.17 <code>.cfi_offset </code><var>register</var><code>, </code><var>offset</var></h3>
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<p>Previous value of <var>register</var> is saved at offset <var>offset</var> from
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CFA.
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<h3 class="section">7.18 <code>.cfi_rel_offset </code><var>register</var><code>, </code><var>offset</var></h3>
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<p>Previous value of <var>register</var> is saved at offset <var>offset</var> from
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the current CFA register. This is transformed to <code>.cfi_offset</code>
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using the known displacement of the CFA register from the CFA.
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This is often easier to use, because the number will match the
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code it's annotating.
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<h3 class="section">7.19 <code>.cfi_register </code><var>register1</var><code>, </code><var>register2</var></h3>
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<p>Previous value of <var>register1</var> is saved in register <var>register2</var>.
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<h3 class="section">7.20 <code>.cfi_restore </code><var>register</var></h3>
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<p><code>.cfi_restore</code> says that the rule for <var>register</var> is now the
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same as it was at the beginning of the function, after all initial
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instruction added by <code>.cfi_startproc</code> were executed.
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<h3 class="section">7.21 <code>.cfi_undefined </code><var>register</var></h3>
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<p>From now on the previous value of <var>register</var> can't be restored anymore.
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<h3 class="section">7.22 <code>.cfi_same_value </code><var>register</var></h3>
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<p>Current value of <var>register</var> is the same like in the previous frame,
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i.e. no restoration needed.
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<h3 class="section">7.23 <code>.cfi_remember_state</code>,</h3>
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<p>First save all current rules for all registers by <code>.cfi_remember_state</code>,
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then totally screw them up by subsequent <code>.cfi_*</code> directives and when
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everything is hopelessly bad, use <code>.cfi_restore_state</code> to restore
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the previous saved state.
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<h3 class="section">7.24 <code>.cfi_return_column </code><var>register</var></h3>
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<p>Change return column <var>register</var>, i.e. the return address is either
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directly in <var>register</var> or can be accessed by rules for <var>register</var>.
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<h3 class="section">7.25 <code>.cfi_signal_frame</code></h3>
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<p>Mark current function as signal trampoline.
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<h3 class="section">7.26 <code>.cfi_window_save</code></h3>
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<p>SPARC register window has been saved.
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<h3 class="section">7.27 <code>.cfi_escape</code> <var>expression</var>[, <small class="dots">...</small>]</h3>
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<p>Allows the user to add arbitrary bytes to the unwind info. One
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might use this to add OS-specific CFI opcodes, or generic CFI
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opcodes that GAS does not yet support.
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<h3 class="section">7.28 <code>.cfi_val_encoded_addr </code><var>register</var><code>, </code><var>encoding</var><code>, </code><var>label</var></h3>
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<p>The current value of <var>register</var> is <var>label</var>. The value of <var>label</var>
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will be encoded in the output file according to <var>encoding</var>; see the
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description of <code>.cfi_personality</code> for details on this encoding.
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<p>The usefulness of equating a register to a fixed label is probably
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limited to the return address register. Here, it can be useful to
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mark a code segment that has only one return address which is reached
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by a direct branch and no copy of the return address exists in memory
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or another register.
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</body></html>
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