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<body><span class="vcard"><a class="email" href="mailto:diana.picus@linaro.org" title="Diana Picus <diana.picus@linaro.org>"> <span class="fn">Diana Picus</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WONTFIX - Gas uses a "Code alignment factor" of 4, MC uses 1"
href="https://llvm.org/bugs/show_bug.cgi?id=30225">bug 30225</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
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<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>WONTFIX
</td>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WONTFIX - Gas uses a "Code alignment factor" of 4, MC uses 1"
href="https://llvm.org/bugs/show_bug.cgi?id=30225#c1">Comment # 1</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WONTFIX - Gas uses a "Code alignment factor" of 4, MC uses 1"
href="https://llvm.org/bugs/show_bug.cgi?id=30225">bug 30225</a>
from <span class="vcard"><a class="email" href="mailto:diana.picus@linaro.org" title="Diana Picus <diana.picus@linaro.org>"> <span class="fn">Diana Picus</span></a>
</span></b>
<pre>I'm not sure this is a bug. AFAICT the code alignment factor in the CIE is only
used to compute offsets for DW_CFA_advance_loc directives, and although the
code alignment factors used by llvm-mc and gas are different, the offsets are
computed correctly.
For instance, for a testcase that I've been playing with gas encodes the
directive
DW_CFA_advance_loc: 12 to 000000000000004c
as
0x43.
The lowest 6 bits mean a delta of 3; multiplied with the code alignment factor
of 4 we obtain an offset of 12.
MC encodes it as 0x4c, which means a delta of 12, multiplied with a code
alignment factor of 1 => again the offset is 12.
I've noticed the same thing with the data alignment factor, which is again
different between gas and MC, but directives such as DW_CFA_offset seem to be
encoded correctly.
So, unless there is something else using these factors that I'm not aware of,
this isn't really a bug. It may be a compatibility issue between gas and MC,
but since each function has its own CIE with its own code/data alignment
factors, debuggers shouldn't have any trouble dealing with this discrepancy.
Feel free to reopen if there are any scenarios where this difference causes
problems.</pre>
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