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<base href="http://llvm.org/bugs/" />
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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 --- - miscompilation with -fPIC, ASAN and #pragma GCC visibility push(hidden)"
href="http://llvm.org/bugs/show_bug.cgi?id=16660">16660</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>miscompilation with -fPIC, ASAN and #pragma GCC visibility push(hidden)
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</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>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kcc@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=10899" name="attach_10899" title="x.ll">attachment 10899</a> <a href="attachment.cgi?id=10899&action=edit" title="x.ll">[details]</a></span>
x.ll
[Initially reported as a crash in asan-ified Firefox:
<a href="https://code.google.com/p/address-sanitizer/issues/detail?id=204">https://code.google.com/p/address-sanitizer/issues/detail?id=204</a>]
x86_64 linux, r186656
Minimized test case:
==> x.cc <==
#pragma GCC visibility push(hidden)
extern __thread int x;
int foo() {
return x;
}
==> y.cc <==
__thread int x;
% clang -O -fsanitize=address x.cc -fPIC -S -o - -emit-llvm | less
define hidden i32 @_Z3foov() #0 {
entry:
%0 = load i8* inttoptr (i64 add (i64 lshr (i64 ptrtoint (i32* @x to i64), i64
3), i64 2147450880) to i8*)
%1 = icmp ne i8 %0, 0
br i1 %1, label %2, label %5
; <label>:2 ; preds = %entry
%3 = icmp sge i8 trunc (i64 add (i64 and (i64 ptrtoint (i32* @x to i64), i64
7), i64 3) to i8), %0
br i1 %3, label %4, label %5
; <label>:4 ; preds = %2
call void @__asan_report_load4(i64 ptrtoint (i32* @x to i64))
call void asm sideeffect "", ""()
unreachable
; <label>:5 ; preds = %2, %entry
%6 = load i32* @x, align 4, !tbaa !0
ret i32 %6
}
% clang -O -fsanitize=address x.cc y.cc -fPIC -shared -o x.so ; objdump -d
x.so | less -pfoo
00000000000007b0 <_Z3foov>:
7b0: 50 push %rax
7b1: 48 8d 3d f8 07 20 00 lea 0x2007f8(%rip),%rdi # 200fb0
<_DYNAMIC+0x1b0>
7b8: e8 f3 fe ff ff callq 6b0 <__tls_get_addr@plt>
7bd: 48 89 c1 mov %rax,%rcx
7c0: 48 8d 89 00 00 00 00 lea 0x0(%rcx),%rcx
7c7: 48 c1 e9 03 shr $0x3,%rcx
7cb: 8a 91 00 80 ff 7f mov 0x7fff8000(%rcx),%dl
7d1: 84 d2 test %dl,%dl
7d3: 74 1a je 7ef <_Z3foov+0x3f>
7d5: 48 89 c1 mov %rax,%rcx
7d8: 48 be c4 0d 20 00 00 movabs $0x200dc4,%rsi
<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ???????????
7df: 00 00 00
7e2: 01 ce add %ecx,%esi
7e4: 83 e6 07 and $0x7,%esi
7e7: 83 c6 03 add $0x3,%esi
7ea: 40 38 d6 cmp %dl,%sil
7ed: 7d 08 jge 7f7 <_Z3foov+0x47>
7ef: 8b 80 00 00 00 00 mov 0x0(%rax),%eax
7f5: 5a pop %rdx
7f6: c3 retq
7f7: 48 8d 80 00 00 00 00 lea 0x0(%rax),%rax
7fe: 48 89 c7 mov %rax,%rdi
801: e8 9a fe ff ff callq 6a0 <__asan_report_load4@plt>
806: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
Here we have a TLS object x, which addressed is used 3 times (one time from the
original code and two times in the asan-added instrumentation).
The LLVM IR looks sane to me, but the assembly is bogus, there is some extra
instruction movabs $0x200dc4,%rsi
San someone help me investigate why does the CG produce this extra instruction?
Just in case, attaching the .ll files:
% llc -relocation-model=pic x.ll; llc -relocation-model=pic y.ll ; gcc -shared
-fPIC x.s y.s -o x.so; objdump -d x.so | less -pfoo</pre>
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