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<h3 class="section">7.10 CFI directives</h3>
<h4 class="subsection">7.10.1 <code>.cfi_sections </code><var>section_list</var></h4>
<p><a name="index-g_t_0040code_007bcfi_005fsections_007d-directive-299"></a><code>.cfi_sections</code> may be used to specify whether CFI directives
should emit <code>.eh_frame</code> section and/or <code>.debug_frame</code> section.
If <var>section_list</var> is <code>.eh_frame</code>, <code>.eh_frame</code> is emitted,
if <var>section_list</var> is <code>.debug_frame</code>, <code>.debug_frame</code> is emitted.
To emit both use <code>.eh_frame, .debug_frame</code>. The default if this
directive is not used is <code>.cfi_sections .eh_frame</code>.
<p>On targets that support compact unwinding tables these can be generated
by specifying <code>.eh_frame_entry</code> instead of <code>.eh_frame</code>.
<h4 class="subsection">7.10.2 <code>.cfi_startproc [simple]</code></h4>
<p><a name="index-g_t_0040code_007bcfi_005fstartproc_007d-directive-300"></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.
<h4 class="subsection">7.10.3 <code>.cfi_endproc</code></h4>
<p><a name="index-g_t_0040code_007bcfi_005fendproc_007d-directive-301"></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>.
<h4 class="subsection">7.10.4 <code>.cfi_personality </code><var>encoding</var><code> [, </code><var>exp</var><code>]</code></h4>
<p><a name="index-g_t_0040code_007bcfi_005fpersonality_007d-directive-302"></a><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.
<h4 class="subsection">7.10.5 <code>.cfi_personality_id </code><var>id</var></h4>
<p><a name="index-g_t_0040code_007bcfi_005fpersonality_005fid_007d-directive-303"></a><code>cfi_personality_id</code> defines a personality routine by its index as
defined in a compact unwinding format.
Only valid when generating compact EH frames (i.e.
with <code>.cfi_sections eh_frame_entry</code>.
<h4 class="subsection">7.10.6 <code>.cfi_fde_data [</code><var>opcode1</var><code> [, ...]]</code></h4>
<p><a name="index-g_t_0040code_007bcfi_005ffde_005fdata_007d-directive-304"></a><code>cfi_fde_data</code> is used to describe the compact unwind opcodes to be
used for the current function. These are emitted inline in the
<code>.eh_frame_entry</code> section if small enough and there is no LSDA, or
in the <code>.gnu.extab</code> section otherwise.
Only valid when generating compact EH frames (i.e.
with <code>.cfi_sections eh_frame_entry</code>.
<h4 class="subsection">7.10.7 <code>.cfi_lsda </code><var>encoding</var><code> [, </code><var>exp</var><code>]</code></h4>
<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>), the second
argument is not present, otherwise the second argument should be a constant
or a symbol name. The default after <code>.cfi_startproc</code> is <code>.cfi_lsda 0xff</code>,
meaning that no LSDA is present.
<h4 class="subsection">7.10.8 <code>.cfi_inline_lsda</code> [<var>align</var>]</h4>
<p><code>.cfi_inline_lsda</code> marks the start of a LSDA data section and
switches to the corresponding <code>.gnu.extab</code> section.
Must be preceded by a CFI block containing a <code>.cfi_lsda</code> directive.
Only valid when generating compact EH frames (i.e.
with <code>.cfi_sections eh_frame_entry</code>.
<p>The table header and unwinding opcodes will be generated at this point,
so that they are immediately followed by the LSDA data. The symbol
referenced by the <code>.cfi_lsda</code> directive should still be defined
in case a fallback FDE based encoding is used. The LSDA data is terminated
by a section directive.
<p>The optional <var>align</var> argument specifies the alignment required.
The alignment is specified as a power of two, as with the
<code>.p2align</code> directive.
<h4 class="subsection">7.10.9 <code>.cfi_def_cfa </code><var>register</var><code>, </code><var>offset</var></h4>
<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>.
<h4 class="subsection">7.10.10 <code>.cfi_def_cfa_register </code><var>register</var></h4>
<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.
<h4 class="subsection">7.10.11 <code>.cfi_def_cfa_offset </code><var>offset</var></h4>
<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.
<h4 class="subsection">7.10.12 <code>.cfi_adjust_cfa_offset </code><var>offset</var></h4>
<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.
<h4 class="subsection">7.10.13 <code>.cfi_offset </code><var>register</var><code>, </code><var>offset</var></h4>
<p>Previous value of <var>register</var> is saved at offset <var>offset</var> from
CFA.
<h4 class="subsection">7.10.14 <code>.cfi_rel_offset </code><var>register</var><code>, </code><var>offset</var></h4>
<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.
<h4 class="subsection">7.10.15 <code>.cfi_register </code><var>register1</var><code>, </code><var>register2</var></h4>
<p>Previous value of <var>register1</var> is saved in register <var>register2</var>.
<h4 class="subsection">7.10.16 <code>.cfi_restore </code><var>register</var></h4>
<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.
<h4 class="subsection">7.10.17 <code>.cfi_undefined </code><var>register</var></h4>
<p>From now on the previous value of <var>register</var> can't be restored anymore.
<h4 class="subsection">7.10.18 <code>.cfi_same_value </code><var>register</var></h4>
<p>Current value of <var>register</var> is the same like in the previous frame,
i.e. no restoration needed.
<h4 class="subsection">7.10.19 <code>.cfi_remember_state</code>,</h4>
<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.
<h4 class="subsection">7.10.20 <code>.cfi_return_column </code><var>register</var></h4>
<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>.
<h4 class="subsection">7.10.21 <code>.cfi_signal_frame</code></h4>
<p>Mark current function as signal trampoline.
<h4 class="subsection">7.10.22 <code>.cfi_window_save</code></h4>
<p>SPARC register window has been saved.
<h4 class="subsection">7.10.23 <code>.cfi_escape</code> <var>expression</var>[, <small class="dots">...</small>]</h4>
<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.
<h4 class="subsection">7.10.24 <code>.cfi_val_encoded_addr </code><var>register</var><code>, </code><var>encoding</var><code>, </code><var>label</var></h4>
<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.
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