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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - LLDB not clearing EXC_BAD_ACCESS exception after `thread return` (on MacOS)?"
href="https://bugs.llvm.org/show_bug.cgi?id=50948">50948</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>LLDB not clearing EXC_BAD_ACCESS exception after `thread return` (on MacOS)?
</td>
</tr>
<tr>
<th>Product</th>
<td>lldb
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>MacOS X
</td>
</tr>
<tr>
<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>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>lldb-dev@lists.llvm.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>vyng@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>jdevlieghere@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Repro:
Using the following test code:
// bad_access.cc
1 // bad_access.cc
2 #include <stdio.h>
3 #include <stdlib.h>
4
5 int bad_acc(void){
6 printf("in bad_acc()\n");
7
8 // cause bad mem access here
9 return *(int*)(123);
10 }
11
12 int main () {
13 printf( "hello world\n");
14 // bad access here
15 bad_acc();
16 printf("bye world\n");
17 return 0;
18 }
vyng-macbookpro2%
// Compile and run with lldb:
% clang -g -o bad_acc bad_access.cc
% lldb
(lldb) target create "bad_acc"
Current executable set to '<path_to>/bad_acc' (x86_64).
(lldb)
Current executable set to '<path_to>/bad_acc' (x86_64).
(lldb) run
Process 97548 launched: '<path_to>/bad_acc' (x86_64)
hello world
in bad_acc()
Process 97548 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=1, address=0x7b)
frame #0: 0x0000000100003f0b bad_acc`bad_acc() at bad_access.cc:9:10
6 printf("in bad_acc()\n");
7
8 // cause bad mem access here
-> 9 return *(int*)(123);
10 }
11
12 int main () {
Target 1: (bad_acc) stopped.
(lldb) thread return
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=1, address=0x7b)
frame #0: 0x0000000100003f45 bad_acc`main at bad_access.cc:16:3
13 printf( "hello world\n");
14 // bad access here
15 bad_acc();
-> 16 printf("bye world\n");
17 return 0;
18 }
(lldb) register write pc `$pc-8`
(lldb) register write pc `$pc-8`
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=1, address=0x7b)
* frame #0: 0x0000000100003f35 bad_acc`main at bad_access.cc:13:3
frame #1: 0x00007fff204e8f5d libdyld.dylib`start + 1
frame #2: 0x00007fff204e8f5d libdyld.dylib`start + 1
(lldb) n
Process 97548 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=1, address=0x27e80d)
frame #0: 0x0000000100003f35 bad_acc`main at bad_access.cc:13:3
10 }
11
12 int main () {
-> 13 printf( "hello world\n");
14 // bad access here
15 bad_acc();
16 printf("bye world\n");
Target 1: (bad_acc) stopped.
------------------------------------------
Details:
After the processed stopped on bad_access.cc:9, I used `thread return` and two
`register write pc `$pc-8`` hoping to get back to bad_access.cc:13 to restart
the exececution.
- Expected behaviour: the exception is cleared and the program restarted.
- What actually happened: exception didn't clear and the program failed to
continue. (Even though `bt` showed that we were now back to line 13).</pre>
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