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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 - [thinlto] -x86-asm-syntax should not affect module level inline asm parsing + link errors"
href="https://bugs.llvm.org/show_bug.cgi?id=46503">46503</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[thinlto] -x86-asm-syntax should not affect module level inline asm parsing + link errors
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</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>enhancement
</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>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, peter@pcc.me.uk
</td>
</tr></table>
<p>
<div>
<pre>(This is the real problem I was trying to understand re: <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - [lto] Module asm symbols don't show in IR symbol table"
href="show_bug.cgi?id=46502">Bug 46502</a>)
Reproducer:
$ cat /tmp/x.c
void foo() {}
asm(".globl bar \n"
"bar: \n"
" xor %eax, %eax\n"
" ret \n");
$ cat /tmp/y.c
extern void foo();
extern void bar();
int main() {
foo();
bar();
return 0;
}
$ build.release/bin/clang-cl -flto=thin -m64 /c /tmp/x.c /tmp/y.c &&
build.release/bin/lld-link /out:a.exe x.obj y.obj /nodefaultlib:oldnames.lib
/nodefaultlib:libcmt.lib /entry:main
error: unknown token in expression
xor %eax, %eax
^
error: unknown token in expression
xor %eax, %eax
^
lld-link: error: undefined symbol: bar
<span class="quote">>>> referenced by /tmp/y.c
>>> y.obj</span >
Note that the asm parsing error and link failure only happens during ThinLTO,
not during normal compilation.
The "unknown token in expression" error comes from clang-cl passing -mllvm
-x86-asm-syntax=intel. That's only supposed to affect the asm dialect used for
*writing*, not for *reading* assembly.
The regular inline asm parser gets this right and defaults to At&t dialect, but
the parser used in ModuleSymbolTable doesn't do this. I believe this is the
right fix:
diff --git a/llvm/lib/Object/ModuleSymbolTable.cpp
b/llvm/lib/Object/ModuleSymbolTable.cpp
index 45bcf748189..b2b09cf27df 100644
--- a/llvm/lib/Object/ModuleSymbolTable.cpp
+++ b/llvm/lib/Object/ModuleSymbolTable.cpp
@@ -23,6 +23,7 @@
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Module.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
@@ -116,6 +117,10 @@ initializeRecordStreamer(const Module &M,
if (!TAP)
return;
+ // Module-level inline asm is assumed to use AT&T syntax (see
+ // AsmPrinter::doInitialization()).
+ Parser->setAssemblerDialect(InlineAsm::AD_ATT);
+
Parser->setTargetParser(*TAP);
if (Parser->Run(false))
return;
However, I can't see exactly what this changes on the object file level (making
it hard to write a test) and also don't fully understand the link failure,
because even when the link fails, the symbol shows up as defined in the symbol
table:
$ build.release/bin/llvm-nm x.obj
---------------- T bar
---------------- T foo
$ build.release/bin/llvm-nm y.obj
U bar
U foo
---------------- T main
I assume there's something else involved in the symbol resolution.
Peter, does this make sense, and what am I missing?</pre>
</div>
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