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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -fasynchronous-unwind-tables fails to produce unwind information for epilogues"
href="https://bugs.llvm.org/show_bug.cgi?id=47142">47142</a>
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<th>Summary</th>
<td>-fasynchronous-unwind-tables fails to produce unwind information for epilogues
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>wittman@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Specifying -fasynchronous-unwind-tables doesn't emit sufficient unwind
information to unwind from function epilogues. In the repro case below the
compiler should be producing unwind information for addresses 0x24 and 0x28 to
account for the changes to sp in the previous instructions, but this is not
happening. Unwinds from those addresses will not work properly as a result.
This was observed in Chromium's clang built from
1bd7046e4ce0102adef6096a12a289d7f94b8c73.
test.cc:
void foo(int a, int b, int c, int d, int e, int f) {}
$ clang -target arm-linux-androideabi16 -g -funwind-tables
-fasynchronous-unwind-tables -fomit-frame-pointer -c test.cc -o test.o
$ objdump -j .text -dC test.o
test.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <foo(int, int, int, int, int, int)>:
0: e92d4800 push {fp, lr}
4: e24dd010 sub sp, sp, #16
8: e59dc01c ldr ip, [sp, #28]
c: e59de018 ldr lr, [sp, #24]
10: e58d000c str r0, [sp, #12]
14: e58d1008 str r1, [sp, #8]
18: e58d2004 str r2, [sp, #4]
1c: e58d3000 str r3, [sp]
20: e28dd010 add sp, sp, #16
24: e8bd4800 pop {fp, lr}
28: e12fff1e bx lr
$ dwarfdump --debug-frame test.o
test.o: file format ELF32-arm-little
.debug_frame contents:
00000000 00000010 ffffffff CIE
Version: 4
Augmentation: ""
Address size: 4
Segment desc size: 0
Code alignment factor: 1
Data alignment factor: -4
Return address column: 14
DW_CFA_def_cfa: reg13 +0
DW_CFA_nop:
DW_CFA_nop:
00000014 00000018 00000000 FDE cie=00000000 pc=00000000...0000002c
DW_CFA_advance_loc: 4
DW_CFA_def_cfa_offset: +8
DW_CFA_offset: reg14 -4
DW_CFA_offset: reg11 -8
DW_CFA_advance_loc: 4
DW_CFA_def_cfa_offset: +24
DW_CFA_nop:
DW_CFA_nop:
.eh_frame contents:</pre>
</div>
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