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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Emitted binary code changes when -g is enabled at -O1 -m32 (interestingly, this behaviour disappears after preprocessing)"
href="https://bugs.llvm.org/show_bug.cgi?id=52540">52540</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Emitted binary code changes when -g is enabled at -O1 -m32 (interestingly, this behaviour disappears after preprocessing)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tlwang@uwaterloo.ca
</td>
</tr>
<tr>
<th>CC</th>
<td>cnsun@uwaterloo.ca, llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Blocks</th>
<td>37728
</td>
</tr></table>
<p>
<div>
<pre>The .text section for the following program (transformed_program0.c) changes
after toggling the -g flag. However, this behaviour goes away after running
transformed_program0.c through the preprocessor.
$ clang-trunk -v
clang version 14.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
82fc4cc60bec6d0eacad7e8575f404dcdf5144c5)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/cnsun/usr/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ cat transformed_program0.c
#include "csmith.h" //
<a href="https://github.com/csmith-project/csmith/blob/master/runtime/csmith.h">https://github.com/csmith-project/csmith/blob/master/runtime/csmith.h</a>
struct a {
int32_t b;
} c;
struct {
uint64_t d;
} i;
int e, f;
int volatile g;
long h[1][3];
struct a volatile j[1][1][1];
void l() {
int k[1];
int o;
int *m = &o;
int *n[][1] = {k, k, k, k, m};
uint32_t p;
int32_t q;
for (;;) {
int32_t *r = n[4];
for (p = 0; p <= 1; p++)
for (c.b = 7; c.b; c.b--) {
int32_t **s = n[4];
if ((*s = n[0][4]) == &o)
if (h[e][0])
break;
for (i.d = 0; i.d <= 4; i.d++) {
uint16_t *aa = l;
q &= *aa = h[p][e + 1], j[i.d][e][p], f || g;
}
}
*r = 0;
}
}
int main() {}
$ clang-trunk -I /usr/local/include/csmith -w -c -m32 -O1
transformed_program0.c -o a.out; objdump --disassemble --section=.text a.out >
no_g.txt
$ clang-trunk -I /usr/local/include/csmith -w -c -m32 -O1 -g
transformed_program0.c -o a.out; objdump --disassemble --section=.text a.out >
g.txt
$ diff no_g.txt g.txt
37,42c37,42
< 65: 8d 04 88 lea (%eax,%ecx,4),%eax
< 68: 05 00 00 00 00 add $0x0,%eax
< 6d: 89 44 24 0c mov %eax,0xc(%esp)
< 71: c7 05 00 00 00 00 07 movl $0x7,0x0
< 78: 00 00 00
< 7b: b9 07 00 00 00 mov $0x7,%ecx
---
<span class="quote">> 65: 8d 84 88 00 00 00 00 lea 0x0(%eax,%ecx,4),%eax
> 6c: 89 44 24 0c mov %eax,0xc(%esp)
> 70: c7 05 00 00 00 00 07 movl $0x7,0x0
> 77: 00 00 00
> 7a: b9 07 00 00 00 mov $0x7,%ecx
> 7f: 90 nop</span >
$
This change in the emitted binary doesn't occur if we preprocess the program.
$ clang -E -I /usr/local/include/csmith transformed_program0.c -o
transformed_program0_preprocessed.c
$ clang-trunk -w -c -m32 -O1 transformed_program0_preprocessed.c -o a.out;
objdump --disassemble --section=.text a.out > no_g.txt
$ clang-trunk -w -c -m32 -O1 -g transformed_program0_preprocessed.c -o a.out;
objdump --disassemble --section=.text a.out > g.txt
$ diff no_g.txt g.txt
$</pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - [meta] Make llvm passes debug info invariant"
href="https://bugs.llvm.org/show_bug.cgi?id=37728">Bug 37728</a>] [meta] Make llvm passes debug info invariant
</li>
</ul>
</div>
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