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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - large position independent x86 code"
href="https://llvm.org/bugs/show_bug.cgi?id=27589">27589</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>large position independent x86 code
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>rafael.espindola@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>hans@chromium.org, llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>When compiling
extern int a;
int *f() {
return &a;
}
Clang generates the following for finding the current ip address:
f:
calll .L0$pb
.L0$pb:
popl %eax
.Ltmp0:
addl $_GLOBAL_OFFSET_TABLE_+(.Ltmp0-.L0$pb), %eax
movl a@GOT(%eax), %eax
ret
which is 19 bytes.
gcc produces
f:
call __x86.get_pc_thunk.ax
addl $_GLOBAL_OFFSET_TABLE_, %eax
movl a@GOT(%eax), %eax
ret
.section
.text.__x86.get_pc_thunk.ax,"axG",@progbits,__x86.get_pc_thunk.ax,comdat
.globl __x86.get_pc_thunk.ax
.hidden __x86.get_pc_thunk.ax
__x86.get_pc_thunk.ax:
movl (%esp), %eax
ret
While the total code is now 21 bytes, f is 17 bytes and __x86.get_pc_thunk.ax
will be merged by the linker.</pre>
</div>
</p>
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