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